Darwin on Trial E-book
Author: Phillip E Johnson
Genre: Biology / Medicine, Science
1991
DARWIN ON TRIAL
by Phillip E. Johnson
(C) Copyright 1991, Phillip E. Johnson
Used with permission of Phillip E. Johnson and
Regnery Gateway Publishing Co.
Electronically Enhanced Text (c) Copyright 1996, World Library(R)
CONTENTS
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Chapter One: The Legal Setting
Chapter Two: Natural Selection
As a Tautology
As a Scientific Hypothesis
As a Deductive Argument
As a Philosophical Necessity
Chapter Three: Mutations Great and Small
Chapter Four: The Fossil Problem
Chapter Five: The Fact of Evolution
Chapter Six: The Vertebrate Sequence
Fish to Amphibians
Amphibians to Reptiles
Reptiles to Mammals
Reptile to Bird
From Apes to Humans
Chapter Seven: The Molecular Evidence
Chapter Eight: Prebiological Evolution
Chapter Nine: The Rules of Science
Chapter Ten: Darwinist Religion
Chapter Eleven: Darwinist Education
Chapter Twelve: Science and Pseudoscience
Research Notes
Chapter One
THE LEGAL SETTING
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IN 1981 THE STATE legislature of Louisiana passed a law requiring
that if "evolution-science" is taught in the public schools, the
schools must also provide balanced treatment for something called
"creation-science." The statute was a direct challenge to the
scientific orthodoxy of today, which is that all living things evolved
by a gradual, natural process- from nonliving matter to simple
micro-organisms, leading eventually to man. Evolution is taught in the
public schools (and presented in the media) not as a theory but as a
fact, the "fact of evolution." There are nonetheless many
dissidents, some with advanced scientific degrees, who deny that
evolution is a fact and who insist that an intelligent Creator
caused all living things to come into being in furtherance of a
purpose.
The conflict requires careful explanation, because the terms are
confusing. The concept of creation in itself does not imply opposition
to evolution, if evolution means only a gradual process by which one
kind of living creature changes into something different. A Creator
might well have employed such a gradual process as a means of
creation. "Evolution" contradicts "creation" only when it is
explicitly or tacitly defined as fully naturalistic evolution- meaning
evolution that is not directed by any purposeful intelligence.
Similarly, "creation" contradicts evolution only when it means
sudden creation, rather than creation by progressive development.
For example, the term "creation-science," as used in the Louisiana
law, is commonly understood to refer to a movement of Christian
fundamentalists based upon an extremely literal interpretation of
the Bible. Creation-scientists do not merely insist that life was
created; they insist that the job was completed in six days no more
than ten thousand years ago, and that all evolution since that time
has involved trivial modifications rather than basic changes.
Because creation-science has been the subject of so much controversy
and media attention, many people assume that anyone who advocates
"creation" endorses the "young earth" position and attributes the
existence of fossils to Noah's flood. Clearing up that confusion is
one of the purposes of this book. *
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* Clearing up confusion requires a careful and consistent use of
terms. In this book, "creation-science" refers to young-earth, six-day
special creation. "Creationism" means belief in creation in a more
general sense. Persons who believe that the earth is billions of years
old, and that simple forms of life evolved gradually to become more
complex forms including humans, are "creationists" if they believe
that a supernatural Creator not only initiated this process but in
some meaningful sense controls it in furtherance of a purpose. As we
shall see, "evolution" (in contemporary scientific usage) excludes not
just creation-science but creationism in the broad sense. By
"Darwinism" I mean fully naturalistic evolution, involving chance
mechanisms guided by natural selection.
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The Louisiana statute and comparable laws in other states grew out
of the long-standing efforts of Christian fundamentalists to
reassert the scientific vitality of the Biblical narrative of creation
against its Darwinist rival. The great landmark in this
Bible-science conflict was the famous Scopes case, the "monkey
trial" of the 1920s, which most Americans know in the legendary
version portrayed in the play and movie Inherit the Wind. The legend
tells of religious fanatics who invade a school classroom to persecute
an inoffensive science teacher, and of a heroic defense lawyer who
symbolizes reason itself in its endless battle against superstition.
As with many legendary incidents the historical record is more
complex. The Tennessee legislature had passed as a symbolic measure
a statute prohibiting the teaching of evolution, which the governor
signed only with the explicit understanding that the ban would not
be enforced. Opponents of the law (and some people who just wanted
to put Dayton, Tennessee, on the map) engineered a test case. A former
substitute teacher named Scopes, who wasn't sure whether he had ever
actually taught evolution, volunteered to be the defendant.
The case became a media circus because of the colorful attorneys
involved. William Jennings Bryan, three-time Democratic presidential
candidate and secretary of state under President Woodrow Wilson, led
the prosecution. Bryan was a Bible believer but not an
uncompromising literalist, in that he thought that the "days" of
Genesis referred not to 24-hour periods but to historical ages of
indefinite duration. He opposed Darwinism largely because he thought
that its acceptance had encouraged the ethic of ruthless competition
that underlay such evils as German militarism and robber baron
capitalism.
The Scopes defense team was led by the famous criminal lawyer and
agnostic lecturer Clarence Darrow. Darrow maneuvered Bryan into taking
the stand as an expert witness on the Bible and humiliated him in a
devastating cross-examination. Having achieved his main purpose,
Darrow admitted that his client had violated the statute and invited
the jury to convict. The trial thus ended in a conviction and a
nominal fine of $100. On appeal, the Tennessee supreme court threw out
the fine on a technicality but held the statute constitutional. From a
legal standpoint the outcome was inconclusive, but as presented to the
world by the sarcastic journalist H. L. Mencken, and later by Broadway
and Hollywood, the "monkey trial" was a public relations triumph for
Darwinism.
The scientific establishment was not exactly covering itself with
glory at the time, however. Although he did not appear at the trial,
the principal spokesman for evolution during the 1920s was Henry
Fairfield Osborn, Director of the American Museum of Natural
History. Osborn relied heavily upon the notorious Piltdown Man fossil,
now known to be a fraud, and he was delighted to confirm the discovery
of a supposedly pre-human fossil tooth by the paleontologist Harold
Cooke in Bryan's home state of Nebraska. Thereafter Osborn prominently
featured "Nebraska Man" (scientific designation: Hesperopithecus
haroldcookii) in his antifundamentalist newspaper articles and radio
broadcasts, until the tooth was discovered to be from a peccary, a
kind of pig. If Osborn had been cross-examined by a lawyer as clever
as Clarence Darrow, and satirized by a columnist as ruthless as H.
L. Mencken, he would have looked as silly as Bryan.
The anti-evolution statutes of the 1920s were not enforced, but
textbook publishers tended to say as little as possible about
evolution to avoid controversy. The Supreme Court eventually held
the statutes unconstitutional in 1968, but by then the fundamentalists
had changed their objective. Creation research institutes were
founded, and books began to appear which attacked the orthodox
interpretation of the scientific evidence and argued that the
geological and fossil record could be harmonized with the Biblical
account. None of this literature was taken seriously by the scientific
establishment or the mass media, but the creation-scientists
themselves became increasingly confident that they had a scientific
case to make.
They also began to see that it was possible to turn the principles
of liberal constitutional law to their advantage by claiming a right
to debate evolutionists on equal terms in school science classes.
Their goal was no longer to suppress the teaching of evolution, but to
get a fair hearing for their own viewpoint. If there is a case to be
made for both sides of a scientific controversy, why should public
school students, for example, hear only one side?
Creation-scientists emphasized that they wanted to present only the
scientific arguments in the schools; the Bible itself was not to be
taught.
Of course mainstream science does not agree that there are two sides
to the controversy, and regards creation-science as a fraud. Equal
time for creation-science in biology classes, the Darwinists like to
say, is like equal time for the theory that it is the stork that
brings babies. But the consensus view of the scientific
establishment is not enshrined in the Constitution. Lawmakers are
entitled to act on different assumptions, at least to the extent
that the courts will let them.
Louisiana's statute never went into effect because a federal judge
promptly held it unconstitutional as an "establishment of religion."
In 1987 the Supreme Court of the United States affirmed this
decision by a seven to two majority. The Louisiana law was
unconstitutional, said the majority opinion by justice William
Brennan, because its purpose "was clearly to advance the religious
viewpoint that a supernatural being created humankind." Not so, said
the dissenting opinion by Justice Antonin Scalia, because "The
people of Louisiana, including those who are Christian
fundamentalists, are quite entitled, as a secular matter, to have
whatever scientific evidence there may be against evolution
presented in their schools, just as Mr. Scopes was entitled to present
whatever scientific evidence there was for it."
Both Justice Brennan and Justice Scalia were in a sense right. The
Constitution excludes religious advocacy from public school
classrooms, and to say that a supernatural being created mankind is
certainly to advocate a religious position. On the other hand, the
Louisiana legislature had acted on the premise that legitimate
scientific objections to "evolution" were being suppressed. Some might
doubt that such objections exist, but the Supreme Court could not
overrule the legislature's judgment on a disputed scientific question,
especially considering that the state had been given no opportunity to
show what balanced treatment would mean in practice. In addition,
the creation-scientists were arguing that the teaching of evolution
itself had a religious objective, namely to discredit the idea that
a supernatural being created mankind. Taking all this into account,
Justice Scalia thought that the Constitution permitted the legislature
to give people offended by the allegedly dogmatic teaching of
evolution a fair opportunity to reply.
As a legal scholar, one point that attracted my attention in the
Supreme Court case was the way terms like "science" and "religion" are
used to imply conclusions that judges and educators might be unwilling
to state explicitly. If we say that naturalistic evolution is science,
and supernatural creation is religion, the effect is not very
different from saying that the former is true and the latter is
fantasy. When the doctrines of science are taught as fact, then
whatever those doctrines exclude cannot be true. By the use of labels,
objections to naturalistic evolution can be dismissed without a fair
hearing.
My suspicions were confirmed by the "friend of the court" argument
submitted by the influential National Academy of Sciences,
representing the nation's most prestigious scientists.
Creation-science is not science, said the Academy in its argument to
the Supreme Court, because
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it fails to display the most basic characteristic of science:
reliance upon naturalistic explanations. Instead, proponents of
"creation-science" hold that the creation of the universe, the
earth, living things, and man was accomplished through supernatural
means inaccessible to human understanding.
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Because creationists cannot perform scientific research to establish
the reality of supernatural creation- that being by definition
impossible- the Academy described their efforts as aimed primarily
at discrediting evolutionary theory.
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"Creation-science" is thus manifestly a device designed to dilute
the persuasiveness of the theory of evolution. The dualistic mode of
analysis and the negative argumentation employed to accomplish this
dilution is, moreover, antithetical to the scientific method.
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The Academy thus defined "science" in such a way that advocates of
supernatural creation may neither argue for their own position nor
dispute the claims of the scientific establishment. That may be one
way to win an argument, but it is not satisfying to anyone who
thinks it possible that God really did have something to do with
creating mankind, or that some of the claims that scientists make
under the heading of "evolution" may be false.
I approach the creation-evolution dispute not as a scientist but
as a professor of law, which means among other things that I know
something about the ways that words are used in arguments. What
first drew my attention to the question was the way the rules of
argument seemed to be structured to make it impossible to question
whether what we are being told about evolution is really true. For
example, the Academy's rule against negative argument automatically
eliminates the possibility that science has not discovered how complex
organisms could have developed. However wrong the current answer may
be, it stands until a better answer arrives. It is as if a criminal
defendant were not allowed to present an alibi unless he could also
show who did commit the crime.
A second point that caught my attention was that the very persons
who insist upon keeping religion and science separate are eager to use
their science as a basis for pronouncements about religion. The
literature of Darwinism is full of anti-theistic conclusions, such
as that the universe was not designed and has no purpose, and that
we humans are the product of blind natural processes that care nothing
about us. What is more, these statements are not presented as personal
opinions but as the logical implications of evolutionary science.
Another factor that makes evolutionary science seem a lot like
religion is the evident zeal of Darwinists to evangelize the world, by
insisting than even non-scientists accept the truth of their theory as
a matter of moral obligation. Richard Dawkins, an Oxford Zoologist who
is one of the most influential figures in evolutionary science, is
unabashedly explicit about the religious side of Darwinism. His 1986
book The Blind Watchmaker is at one level about biology, but at a more
fundamental level it is a sustained argument for atheism. According to
Dawkins, "Darwin made it possible to be an intellectually fulfilled
atheist."
When he contemplates the perfidy of those who refuse to believe,
Dawkins can scarcely restrain his fury. "It is absolutely safe to
say that, if you meet somebody who claims not to believe in evolution,
that person is ignorant, stupid or insane (or wicked, but I'd rather
not consider that)." Dawkins went on to explain, by the way, that what
he dislikes particularly about creationists is that they are
intolerant.
We must therefore believe in evolution or go to the madhouse, but
what precisely is it that we are required to believe? "Evolution"
can mean anything from the uncontroversial statement that bacteria
"evolve" resistance to antibiotics to the grand metaphysical claim
that the universe and mankind "evolved" entirely by purposeless,
mechanical forces. A word that elastic is likely to mislead, by
implying that we know as much about the grand claim as we do about the
small one.
That very point was the theme of a remarkable lecture given by Colin
Patterson at the American Museum of Natural History in 1981. Patterson
is a senior paleontologist at the British Natural History Museum and
the author of that museum's general text on evolution. His lecture
compared creationism (not creation-science) with evolution, and
characterized both as scientifically vacuous concepts which are held
primarily on the basis of faith. Many of the specific points in the
lecture are technical, but two are of particular importance for this
introductory chapter. First, Patterson asked his audience of experts a
question which reflected his own doubts about much of what has been
thought to be secure knowledge about evolution:
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Can you tell me anything you know about evolution, any one
thing... that is true? I tried that question on the geology staff at
the Field Museum of Natural History and the only answer I got was
silence. I tried it on the members of the Evolutionary Morphology
seminar in the University of Chicago, a very prestigious body of
evolutionists, and all I got there was silence for a long time and
eventually one person said "I do know one thing- it ought not to be
taught in high school."
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Patterson suggested that both evolution and creation are forms of
pseudo-knowledge, concepts which seem to imply information but do not.
One point of comparison was particularly striking. A common
objection to creationism in pre-Darwinian times was that no one
could say anything about the mechanism of creation. Creationists
simply pointed to the "fact" of creation and conceded ignorance of the
means. But now, according to Patterson, Darwin's theory of natural
selection is under fire and scientists are no longer sure of its
general validity. Evolutionists increasingly talk like creationists in
that they point to a fact but cannot provide an explanation of the
means.
Patterson was being deliberately provocative, and I do not mean to
imply that his skeptical views are widely supported in the
scientific community. On the contrary, Patterson came under heavy fire
from Darwinists after somebody circulated a bootleg transcript of
the lecture, and he eventually disavowed the whole business. Whether
or not he meant to speak for public attribution, however, he was
making an important point. We can point to a mystery and call it
"evolution," but this is only a label. The important question is not
whether scientists have agreed on a label, but how much they know
about how complex living beings like ourselves came into existence.
Irving Kristol is a prominent social theorist with a talent for
recognizing ideological obfuscation, and he applied that talent to
Darwinism in an essay in The New York Times. Kristol observed that
Darwinian theory, which explains complex life as the product of
small genetic mutations and "survival of the fittest," is known to
be valid only for variations within the biological species. That
Darwinian evolution can gradually transform one kind of creature
into another is merely a biological hypothesis, not a fact. He noted
that science abounds with rival opinions about the origin of life
and that some scientists have questioned whether the word
"evolution" carries much meaning. Kristol conceded that
creation-science is a matter of faith and not science, and should
not be taught in the schools, but he thought that its defenders
still had a point:
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It is reasonable to suppose that if evolution were taught more
cautiously, as a conglomerate idea consisting of conflicting
hypotheses rather than as an unchallengeable certainty, it would be
far less controversial. As things now stand, the religious
fundamentalists are not far off the mark when they assert that
evolution, as generally taught, has an unwarranted anti-religious edge
to it.
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One famous evolutionist who might have been expected to be
sympathetic to Kristol's point would be Harvard Professor Stephen
Jay Gould. In 1980 Gould published a paper in a scientific journal
predicting the emergence of "a new and general theory of evolution" to
replace the neo-Darwinian synthesis. Gould wrote that, although he had
been "beguiled" by the unifying power of the Darwinist synthesis
when he studied it as a graduate student in the 1960s, the weight of
the evidence had driven him to the reluctant conclusion that the
synthesis, "as a general proposition, is effectively dead, despite its
persistence as textbook orthodoxy." The dogmatic teaching of that dead
textbook orthodoxy was precisely what Kristol was criticizing.
Gould nonetheless wrote a reply to Kristol that put this outsider
firmly in his place. Gould denied that textbook bias was more
prevalent in evolution than in other fields of science, denied that
evolutionary science is anti-religious, and insisted that "Darwinian
selection... will remain a central focus of more inclusive
evolutionary theories." His main point was that Kristol had ignored
a "central distinction between secure fact and healthy debate about
theory." Biologists do teach evolutionary theory as a conglomerate
idea consisting of conflicting hypotheses, Gould wrote, but
evolution is also a fact of nature, as well established as the fact
that the earth revolves around the sun. *
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* Gould's arguments for the "fact of evolution" are the subject of
Chapters Five and Six of this book.
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As an outside observer who enjoys following the literature of
evolution and its conflicts, I have become accustomed to seeing this
sort of evasive response to criticism. When outsiders question whether
the theory of evolution is as secure as we have been led to believe,
we are firmly told that such questions are out of order. The arguments
among the experts are said to be about matters of detail, such as
the precise timescale and mechanism of evolutionary transformations.
These disagreements are signs not of crisis but of healthy creative
ferment within the field, and in any case there is no room for doubt
whatever about something called the "fact" of evolution.
But consider Colin Patterson's point that a fact of evolution is
vacuous unless it comes with a supporting theory. Absent an
explanation of how fundamental transformations can occur, the bare
statement that "humans evolved from fish" is not impressive. What
makes the fish story impressive, and credible, is that scientists
think they know how a fish can be changed into a human without
miraculous intervention.
Charles Darwin made evolution a scientific concept by showing, or
claiming to have shown, that major transformations could occur in very
small steps by purely natural means, so that time, chance, and
differential survival could take the place of a miracle. If Darwin's
scenario of gradual adaptive change is wrong, then "evolution" may
be no more than a label we attach to the observation that men and fish
have certain common features, such as the vertebrate body plan.
Disagreements about the mechanism of evolution are therefore of
fundamental importance to those of us who want to know whether the
scientists really know as much as they have been claiming to know.
An adequate theory of how evolution works is particularly
indispensable when evolution is deemed to imply, as countless
Darwinists have insisted, that purposeless material mechanisms are
responsible for our existence. "Evolution" in the sense in which these
scientists use the term is a mechanistic process, and so the content
of any "fact" that is left when the mechanism is subtracted is
thoroughly obscure.
In the chapters to follow I will look at the evidence to see whether
a mechanism is known that can accomplish the large-scale changes which
the theory of evolution supposes to have occurred, such as the
change from single-celled bacteria to complex plants and animals, from
fish to mammals, and from apes to men. If the neo-Darwinist
mechanism will not do the job, and if instead of an established
replacement we have only what Gould and Kristol agreed to call "a
conglomerate idea consisting of conflicting hypotheses," then we may
conclude that the scientists do not in fact know how large-scale
evolution could have occurred. We will then have to consider whether a
"fact of evolution" can be separated from Darwin's theory. Our
investigation will require us to explore the new evidence revealed
by molecular studies, the state of research into the origin of life,
and the rules of scientific inquiry.
Before undertaking this task I should say something about my
qualifications and purpose. I am not a scientist but an academic
lawyer by profession, with a specialty in analyzing the logic of
arguments and identifying the assumptions that lie behind those
arguments. This background is more appropriate than one might think,
because what people believe about evolution and Darwinism depends very
heavily on the kind of logic they employ and the kind of assumptions
they make. * Being a scientist is not necessarily an advantage when
dealing with a very broad topic like evolution, which cuts across many
scientific disciplines and also involves issues of philosophy.
Practicing scientists are of necessity highly specialized, and a
scientist outside his field of expertise is just another layman.
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* When the National Academy of Sciences appointed a special
committee to prepare its official booklet titled Science and
Creationism, four of the eleven members were lawyers.
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Access to the relevant scientific information presents no great
difficulty. Charles Darwin and T. H. Huxley wrote for the general
reader, and the same is true of the giants of the neo-Darwinist
synthesis such as Theodosius Dobzhansky, George Gaylord Simpson, and
Julian Huxley. Current authors who address the general public and
who are eminent among scientists include Stephen Jay Gould, Richard
Dawkins, Douglas Futuyma, and a host of other experts who are named in
the research notes to each chapter.
Most of the professional scientific literature is available in the
premier scientific journals Nature and Science, the most prestigious
scientific organs in Britain and America respectively, and at a
somewhat more popular level in the British New Scientist and the
Scientific American. Philosophers and historians have also produced
well-informed books. In short the available literature is
voluminous, and the leading scientific figures have always assumed
that nonscientist readers can understand the essential evidence. But
evidence never speaks for itself; it has meaning only in the context
of rules of reasoning which determine what may be considered and
what counts as evidence. Those rules of reasoning are what I
particularly want to examine.
The last subject I should address before beginning is my personal
religious outlook, because readers are bound to wonder and because I
do not exempt myself from the general rule that bias must be
acknowledged and examined. I am a philosophical theist and a
Christian. I believe that a God exists who could create out of nothing
if He wanted to do so, but who might have chosen to work through a
natural evolutionary process instead. I am not a defender of
creation-science, and in fact I am not concerned in this book with
addressing any conflicts between the Biblical accounts and the
scientific evidence.
My purpose is to examine the scientific evidence on its own terms,
being careful to distinguish the evidence itself from any religious or
philosophical bias that might distort our interpretation of that
evidence. I assume that the creation-scientists are biased by their
precommitment to Biblical fundamentalism, and I will have very
little to say about their position. The question I want to investigate
is whether Darwinism is based upon a fair assessment of the scientific
evidence, or whether it is another kind of fundamentalism.
Do we really know for certain that there exists some natural process
by which human beings and all other living beings could have evolved
from microbial ancestors, and eventually from non-living matter?
When the National Academy of Sciences tells us that reliance upon
naturalistic explanations is the most basic characteristic of science,
is it implying that scientists somehow know that a Creator played no
part in the creation of the world and its forms of life? Can something
be non-science but true, or does non-science mean nonsense? Given
the emphatic endorsement of naturalistic evolution by the scientific
community, can outsiders even contemplate the possibility that this
officially established doctrine might be false? Well, come along and
let us see.
Chapter Two
NATURAL SELECTION
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THE STORY OF Charles Darwin has been told many times, and no wonder.
The relationship with the lawyer-geologist Charles Lyell, the long
voyage in the Beagle with the temperamental Captain Fitzroy, the
observations and adventures in South America and the Galapagos
Islands, the long years of preparation and delay, the eventual
rushed publication of The Origin of Species when Alfred Russell
Wallace appeared about to publish a similar theory, the
controversies and the smashing triumph- all these make a great saga
which is always worth another retelling. My subject is not history but
the logic of current controversy, however, and so my interest must
be in Darwinism and not Darwin. I am also uninterested in the
differences between the theory as Darwin originally proposed it and as
it is understood by neo-Darwinists today, who have the advantage of
the greater understanding of genetics that science has achieved
since Darwin's time. My purpose is to explain what concepts the
contemporary theory employs, what significant statements about the
natural world it makes, and what points of legitimate controversy
there may be.
Darwin's classic book argued three important related propositions.
The first was that "the species are not immutable." By this he meant
that new species have appeared during the long course of the earth's
history by a natural process he called "descent with modification."
The second proposition was that this evolutionary process can be
extended to account for all or nearly all the diversity of life,
because all living things descended from a very small number of common
ancestors, perhaps a single microscopic ancestor. The third
proposition, and the one most distinctive to Darwinism, was that
this vast process was guided by natural selection or "survival of
the fittest," a guiding force so effective that it could accomplish
prodigies of biological craftsmanship that people in previous times
had thought to require the guiding hand of a creator. * The evidence
for this third proposition is the subject of this chapter.
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* Darwin did not insist that all evolution was by natural selection,
nor do his successors. He wrote at the end of the introduction to
the first (1859) edition of The Origin of Species that "I am convinced
that natural selection has been the main but not the exclusive means
of modification" and later complained of the "steady
misrepresentation" that had ignored this qualification. On the other
hand, Darwin was vague about the importance of the alternatives, one
of which was "variations which seem to us in our ignorance to arise
spontaneously." Contemporary neo-Darwinists also practice a tactically
advantageous flexibility concerning the frequency and importance of
non-selective evolution. Stephen Jay Gould wrote that this imprecision
"imposes a great frustration upon anyone who would characterize the
modern synthesis in order to criticize it," and I am sure that every
critic shares the frustration. Readers should therefore beware of
taking at face value claims by neo-Darwinist authorities that some
critic has misunderstood or mischaracterized their theory.
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The question is not whether natural selection occurs. Of course it
does, and it has an effect in maintaining the genetic fitness of a
population. Infants with severe birth defects do not survive to
maturity without expensive medical care, and creatures which do not
survive to reproduce do not leave descendants. These effects are
unquestioned, but Darwinism asserts a great deal more than merely that
species avoid genetic deterioration due to natural attrition among the
genetically unfit. Darwinists claim that this same force of
attrition has a building effect so powerful that it can begin with a
bacterial cell and gradually craft its descendants over billions of
years to produce such wonders as trees, flowers, ants, birds, and
humans. How do we know that all this is possible?
Darwinian evolution postulates two elements. The first is what
Darwin called "variation," and what scientists today call mutation. *
Mutations are randomly occurring genetic changes which are nearly
always harmful when they produce effects in the organism large
enough to be visible, but which may occasionally slightly improve
the organism's ability to survive and reproduce. Organisms generally
produce more offspring than can survive to maturity, and offspring
that possess an advantage of this kind can be expected to produce more
descendants themselves, other things being equal, than less advantaged
members of the species. As the process of differential survival
continues, the trait eventually spreads throughout the species, and it
may become the basis for further cumulative improvements in succeeding
generations. Given enough time, and sufficient mutations of the
right sort, enormously complex organs and patterns of adaptive
behavior can eventually be produced in tiny cumulative steps,
without the assistance of any pre-existing intelligence.
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* "Mutation" as used here is a simple label for the set of
mechanisms which provide the genetic variation upon which natural
selection can go to work. The set includes point mutations,
chromosomal doubling, gene duplication, and recombination. The
essential point is that the variations are supposed to be random.
Creative evolution would be much easier to envisage if some guiding
force caused the right mutations to arrive on schedule. Orthodox
genetic theory insists that no such guiding principle for mutation
exists, so creatures have to make do with whatever blind nature
happens to provide.
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That is, all this can happen if the theory is true. Darwin could not
point to impressive examples of natural selection in action, and so he
had to rely heavily on an argument by analogy. In the words of Douglas
Futuyma:
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When Darwin wrote The Origin of Species, he could offer no good
cases of natural selection because no one had looked for them. He drew
instead an analogy with the artificial selection that animal and Plant
breeders use to improve domesticated varieties of animals and
plants. By breeding only from the woolliest sheep, the most fertile
chickens, and so on, breeders have been spectacularly successful in
altering almost every imaginable characteristic of our domesticated
animals and plants to the point where most of them differ from their
wild ancestors far more than related species differ from them.
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The analogy to artificial selection is misleading. Plant and
animal breeders employ intelligence and specialized knowledge to
select breeding stock and to protect their charges from natural
dangers. The point of Darwin's theory, however, was to establish
that purposeless natural processes can substitute for intelligent
design. That he made that point by citing the accomplishments of
intelligent designers proves only that the receptive audience for
his theory was highly uncritical.
Artificial selection is not basically the same sort of thing as
natural selection, but rather is something fundamentally different.
Human breeders produce variations among sheep or pigeons for
purposes absent in nature, including sheer delight in seeing how
much variation can be achieved. If the breeders were interested only
in having animals capable of surviving in the wild, the extremes of
variation would not exist. When domesticated animals return to the
wild state, the most highly specialized breeds quickly perish and
the survivors revert to the original wild type. Natural selection is a
conservative force that prevents the appearance of the extremes of
variation that human breeders like to encourage.
What artificial selection actually shows is that there are
definite limits to the amount of variation that even the most highly
skilled breeders can achieve. Breeding of domestic animals has
produced no new species, in the commonly accepted sense of new
breeding communities that are infertile when crossed with the parent
group. For example, all dogs form a single species because they are
chemically capable of interbreeding, although inequality of size in
some cases makes natural copulation impracticable. The eminent
French zoologist Pierre Grasse concluded that the results of
artificial selection provide powerful testimony against Darwin's
theory:
-
In spite of the intense pressure generated by artificial selection
(eliminating any parent not answering the criteria of choice) over
whole millennia, no new species are born. A comparative study of sera,
hemoglobins, blood proteins, interfertility, etc., proves that the
strains remain within the same specific definition. This is not a
matter of opinion or subjective classification, but a measurable
reality. The fact is that selection gives tangible form to and gathers
together all the varieties a genome is capable of producing, but
does not constitute an innovative evolutionary process.
-
In other words, the reason that dogs don't become as big as
elephants, much less change into elephants, is not that we just
haven't been breeding them long enough. Dogs do not have the genetic
capacity for that degree of change, and they stop getting bigger
when the genetic limit is reached.
Darwinists disagree with that judgment, and they have some points to
make. They point with pride to experiments with laboratory fruitflies.
These have not produced anything but fruitflies, but they have
produced changes in a multitude of characteristics. Plant hybrids have
been developed which can breed with each other, but not with the
parent species, and which therefore meet the accepted standard for new
species. With respect to animals, Darwinists attribute the inability
to produce new species to a lack of sufficient time. Humans have
been breeding dogs for only a few thousand years, but nature has
millions and even hundreds of millions of years at her disposal. In
some cases, convincing circumstantial evidence exists of evolution
that has produced new species in nature. Familiar examples include the
hundreds of fruitfly species in Hawaii and the famous variations among
"Darwin's Finches" on the Galapagos Islands.
The time available unquestionably has to be taken into account in
evaluating the results of breeding experiments, but it is also
possible that the greater time available to nature may be more than
counterbalanced by the power of intelligent purpose which is brought
to bear in artificial selection. With respect to the famous fruitfly
experiments, for example, Grasse- noted that "The fruitfly (drosophila
melanogaster) the favorite pet insect of the geneticists, whose
geographical, biotropical, urban, and rural genotypes are now known
inside out, seems not to have changed since the remotest times."
Nature has had plenty of time, but it just hasn't been doing what
the experimenters have been doing.
Lack of time would be a reasonable excuse if there were no other
known factor limiting the change that can be produced by selection,
but in fact selective change is limited by the inherent variability in
the gene pool. After a number of generations the capacity for
variation runs out. It might conceivably be renewed by mutation, but
whether (and how often) this happens is not known.
Whether selection has ever accomplished speciation (i.e. the
production of a new species) is not the point. A biological species is
simply a group capable of interbreeding. Success in dividing a
fruitfly population into two or more separate populations that
cannot interbreed would not constitute evidence that a similar process
could in time produce a fruitfly from a bacterium. If breeders one day
did succeed in producing a group of dogs that can reproduce with
each other but not with other dogs, they would still have made only
the tiniest step towards proving Darwinism's important claims.
That the analogy to artificial selection is defective does not
necessarily mean that Darwin's theory is wrong, but it does mean
that we will have to look for more direct evidence to see if natural
selection really does have a creative effect. Before looking at what
the Darwinists have been able to come up with, however, we need to ask
whether evidence is even necessary. Strange as it may seem, there
are many statements in the Darwinist literature to the effect that the
validity of the theory can be demonstrated simply as a matter of
logic.
NATURAL SELECTION AS A TAUTOLOGY
-
Many of the most prominent neo-Darwinists have written at one time
or another that natural selection is a tautology, a way of saying
the same thing twice. In this formulation the theory predicts that the
fittest organisms will produce the most offspring, and it defines
the fittest organisms as the ones which produce the most offspring. It
is important to document this point, because many Darwinists have
convinced themselves that the tautology idea is a misunderstanding
introduced into the literature by creationists and other
uncomprehending faultfinders. But here are a few examples collected by
Norman Macbeth:
-
J. B. S. Haldane (1935): "...the phrase, 'survival of the
fittest,' is something of a tautology. So are most mathematical
theorems. There is no harm in saying the same truth in two different
ways."
-
Ernst Mayr (1963): "...those individuals that have the most
offspring are by definition... the fittest ones."
-
George Gaylord Simpson (1964): "Natural selection favors fitness
only if you define fitness as leaving more descendants. In fact
geneticists do define it that way, which may be confusing to others.
To a geneticist fitness has nothing to do with health, strength,
good looks, or anything but effectiveness in breeding."
-
The explanation by Simpson just quoted indicates why it is not
easy to formulate the theory of natural selection other than as a
tautology. It may seem obvious, for example, that it is advantageous
for a wild stallion to be able to run faster, but in the Darwinian
sense this will be true only to the extent that a faster stallion
sires more offspring. If greater speed leads to more frequent falls,
or if faster stallions tend to outdistance the mares and miss
opportunities for reproduction, then the improvement may be
disadvantageous.
Just about any characteristic can be either advantageous or
disadvantageous, depending upon the surrounding environmental
conditions. Does it seem that the ability to fly is obviously an
advantage? Darwin hypothesized that natural selection might have
caused beetles on Madeira to lose the ability to fly, because
beetles capable of flight tended to be blown out to sea. The large
human brain requires a large skull which causes discomfort and
danger to the mother in childbirth. We assume that our brain size is
advantageous because civilized humans dominate the planet, but it is
far from obvious that the large brain was a net advantage in the
circumstances in which it supposedly evolved. Among primates in
general, those with the largest brains are not the ones least in
danger of extinction.
In all such cases we can presume a characteristic to be advantageous
because a species which has it seems to be thriving, but in most cases
it is impossible to identify the advantage independently of the
outcome. That is why Simpson was so insistent that "advantage" has
no inherent meaning other than actual success in reproduction. All
we can say is that the individuals which produced the most offspring
must have had the qualities required for producing the most offspring.
The famous philosopher of science Karl Popper at one time wrote that
Darwinism is not really a scientific theory because natural
selection is an all-purpose explanation which can account for
anything, and which therefore explains nothing. Popper backed away
from this position after he was besieged by indignant Darwinist
protests, but he had plenty of justification for taking it. As he
wrote in his own defense, "some of the greatest contemporary
Darwinists themselves formulate the theory in such a way that it
amounts to the tautology that those organisms that leave most
offspring leave most offspring," citing Fisher, Haldane, Simpson, "and
others." One of the others was C. H. Waddington, whose attempt to make
sense of the matter deserves to be preserved for posterity:
-
Darwin's major contribution was, of course, the suggestion that
evolution can be explained by the natural selection of random
variations. Natural selection, which was at first considered as though
it were a hypothesis that was in need of experimental or observational
confirmation, turns out on closer inspection to be a tautology, a
statement of an inevitable but previously unrecognized relation. It
states that the fittest individuals in a population (defined as
those which leave most offspring) will leave most offspring. This fact
in no way reduces the magnitude of Darwin's achievement; only after it
was clearly formulated, could biologists realize the enormous power of
the principle as a weapon of explanation.
-
That was not an offhand statement, but a considered judgment
published in a paper presented at the great convocation at the
University of Chicago in 1959 celebrating the hundredth anniversary of
the publication of The Origin of Species. Apparently, none of the
distinguished authorities present told Waddington that a tautology
does not explain anything. When I want to know how a fish can become a
man, I am not enlightened by being told that the organisms that
leave the most offspring are the ones that leave the most offspring.
It is not difficult to understand how leading Darwinists were led to
formulate natural selection as a tautology. The contemporary
neo-Darwinian synthesis grew out of population genetics, a field
anchored in mathematics and concerned with demonstrating how rapidly
very small mutational advantages could spread in a population. The
advantages in question were assumptions in a theorem, not qualities
observed in nature, and the mathematicians naturally tended to think
of them as "whatever it was that caused the organism and its
descendants to produce more offspring than other members of the
species." This way of thinking spread to the zoologists and
paleontologists, who found it convenient to assume that their
guiding theory was simply true by definition. As long as outside
critics were not paying attention, the absurdity of the tautology
formulation was in no danger of exposure.
What happened to change this situation is that Popper's comment
received a great deal of publicity, and creationists and other
unfriendly critics began citing it to support their contention that
Darwinism is not really a scientific theory. The Darwinists themselves
became aware of a dangerous situation, and thereafter critics
raising the tautology claim were firmly told that they were simply
demonstrating their inability to understand Darwinism. As we shall see
in later chapters, however, in practice natural selection continues to
be employed in its tautological formulation.
If the concept of natural selection were really only a tautology I
could end the chapter at this point, because a piece of empty
repetition obviously does not have the power to guide an
evolutionary process in its long journey from the first replicating
macro-molecule to modern human beings. But although natural
selection can be formulated as a tautology, and often has been, it can
also be formulated in other ways that are not so easily dismissed.
We must go on to consider these other possibilities.
NATURAL SELECTION AS A DEDUCTIVE ARGUMENT
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Visitors to the British Natural History Museum will find prominently
on sale the museum's handbook on evolution, written by
paleontologist Colin Patterson. When he considers the scientific
status of Darwinism, Patterson writes that the theory can be presented
in the form of a deductive argument, for example:
-
1. All organisms must reproduce;
2. All organisms exhibit hereditary variations;
3. Hereditary variations differ in their effect on reproduction;
4. Therefore variations with favorable effects on reproduction
will succeed, those with unfavorable effects will fail, and
organisms will change.
-
Patterson observes that the theorem establishes only that some
natural selection will occur, not that it is a general explanation for
evolution. Actually, the theorem does not even establish that
organisms will change. The range of hereditary variations may be
narrow, and the variations which survive may be just favorable
enough to keep the species as it is. Possibly the species would change
a great deal more (in the direction of eventual extinction) if the
least favored individuals most often succeeded in reproducing their
kind. That the effect of natural selection may be to keep a species
from changing is not merely a theoretical possibility. As we shall see
in Chapter Four, the prevailing characteristic of fossil species is
stasis- the absence of change. There are numerous "living fossils"
which are much the same today as they were millions of years ago, at
least as far as we can determine.
Patterson is not the only evolutionist who thinks of natural
selection as a matter of deductive logic, although most who have
used this formulation have thought more highly of the theory than he
appears to do. For example, origin of life researcher A. G.
Cairns-Smith employed the syllogistic formulation (substantially as
Darwin himself stated it) to explain how complex organisms can
evolve from very simple ones:
-
Darwin persuades us that the seemingly purposeful construction of
living things can very often, and perhaps always, be attributed to the
operation of natural selection. If you have things that are
reproducing their kind; if there are sometimes random variations,
nevertheless, in the offspring; if such variations can be inherited;
if some such variations can sometimes confer an advantage on their
owners; if there is competition between the reproducing entities;-
if there is an overproduction so that not all will be able to
produce offspring themselves- then these entities will get better at
reproducing their kind. Nature acts as a selective breeder in these
circumstances: the stock cannot help but improve.
-
In fact the stock is often highly successful at resisting
improvement, often for millions of years, so there must be something
wrong with the logic. This time it is the confusion generated by
that word "advantage." Advantage in the proper Darwinist sense, as
George Gaylord Simpson explained for us, does not mean improvement
as humans measure it. Ants and bacteria are just as advantaged as we
are, judged by the exclusive criterion of success in reproduction.
In any population some individuals will leave more offspring than
others, even if the population is not changing or is headed straight
for extinction.
NATURAL SELECTION AS A SCIENTIFIC HYPOTHESIS
-
Up to this point we have been disposing of some simple fallacies
to clear the field of distractions, but now we get to the important
category which deserves our most respectful scrutiny. I am sure that
today most evolutionary scientists would insist that Darwinistic
natural selection is a scientific hypothesis which has been so
thoroughly tested and confirmed by the evidence that it should be
accepted by reasonable persons as a presumptively adequate explanation
for the evolution of complex life forms. The hypothesis, to be
precise, is that natural selection (in combination with mutation) is
an innovative evolutionary process capable of producing new kinds of
organs and organisms. That brings us to the critical question: what
evidence confirms that this hypothesis is true?
Douglas Futuyma has done the best job of marshalling the
supporting evidence, and here are the examples he gives of
observations that confirm the creative effectiveness of natural
selection:
-
1. Bacteria naturally develop resistance to antibiotics, and
insect pests become resistant to insecticides, because of the
differential survival of mutant forms possessing the advantage of
resistance.
-
2. In 1898 a severe storm in Massachusetts left hundreds of dead and
dying birds in its wake. Someone brought 136 exhausted sparrows to a
scientist named Bumpus, I imagine so they could be cared for, but
Bumpus was made of sterner stuff and killed the survivors to measure
their skeletons. He found that among male sparrows the larger birds
had survived more frequently than the smaller ones, even though the
size differential was relatively slight.
-
3. A drought in the Galapagos Islands in 1977 caused a shortage of
the small seeds on which finches feed. As a consequence these birds
had to eat larger seeds, which they usually ignore. After one
generation there had been so much mortality among the smaller finches,
who could not easily eat the larger seeds, that the average size of
the birds (and especially their beaks) went up appreciably. Futuyma
comments: "Very possibly the birds will evolve back to their
previous state if the environment goes back to normal, * but we can
see in this example what would happen if the birds were forced to live
in a consistently dry environment: they would evolve a permanent
adaptation to whatever kinds of seeds are consistently available. This
is natural selection in action, and it is not a matter of chance."
-
* In fact this is exactly what happened. The article "Oscillating
Selection on Darwin's Finches" by Gibbs and Grant [Nature, vol. 327,
p. 511, 1987] reports that small adults survived much better than
large ones following the wet year 1982-83, completely reversing the
trend of 1977-82.
-
4. The allele (genetic state) responsible for sickle-cell anemia
in African populations is also associated with a trait that confers
resistance to malaria. Individuals who are totally free of the
sickle-cell allele suffer high mortality from malaria, and individuals
who inherit the sickle-cell allele from both parents tend to die early
from anemia. Chances for survival are greatest when the individual
inherits the sickle-cell allele from one parent but not the other, and
so the trait is not bred out of the population. Futuyma comments
that the example shows not only that natural selection is effective,
but also that it is "an uncaring mechanical process."
-
5. Mice populations have been observed to cease reproducing and
become extinct when they are temporarily "flooded" by the spread of
a gene which causes sterility in the males.
-
6. Finally, Futuyma summarizes Kettlewell's famous observations of
"industrial melanism" in the peppered moth. When trees were darkened
by industrial smoke, dark-colored (melanic) moths became abundant
because predators had difficulty seeing them against the trees. When
the trees became lighter due to reduced air pollution, the
lighter-colored moths had the advantage. Kettlewell's observations
showed in detail how the prevailing color of moths changed along
with the prevailing color of the trees. Subsequent commentators have
observed that the example shows stability as well as cyclical change
within a boundary, because the ability of the species to survive in
a changing environment is enhanced if it maintains at all times a
supply of both light and dark moths. If the light variety had
disappeared altogether during the years of dark trees, the species
would have been threatened with extinction when the trees lightened.
There are a few other examples in Futuyma's chapter, but I believe
they are meant as illustrations to show how Darwinism accounts for
certain anomalies like self-sacrificing behavior and the peacock's fan
rather than as additional examples of observations confirming the
effect of natural selection in producing change. If we take these
six examples as the best available observational evidence of natural
selection, we can draw two conclusions:
-
1. There is no reason to doubt that peculiar circumstances can
sometimes favor drug-resistant bacteria, or large birds as opposed
to small ones, or dark-colored moths as opposed to light-colored ones.
In such circumstances the population of drug-susceptible bacteria,
small birds, and light-colored moths may become reduced for some
period of time, or as long as the circumstances prevail.
-
2. None of the "proofs" provides any persuasive reason for believing
that natural selection can produce new species, new organs, or other
major changes, or even minor changes that are permanent. The
sickle-cell anemia case, for example, merely shows that in special
circumstances an apparently disadvantageous trait may not be
eliminated from the population. That larger birds have an advantage
over smaller birds in high winds or droughts has no tendency
whatever to prove that similar factors caused birds to come into
existence in the first place. Very likely smaller birds have the
advantage in other circumstances, which explains why birds are not
continually becoming larger.
-
Pierre Grasse was as unimpressed by this kind of evidence as I am,
and he summarized his conclusions at the end of his chapter on
evolution and natural selection:
-
The "evolution in action" of J. Huxley and other biologists is
simply the observation of demographic facts, local fluctuations of
genotypes, geographical distributions. Often the species concerned
have remained practically unchanged for hundreds of centuries!
Fluctuation as a result of circumstances, with prior modification of
the genome, does not imply evolution, and we have tangible proof of
this in many panchronic species [i.e. living fossils that remain
unchanged for millions of years]...
-
This conclusion seems so obviously correct that it gives rise to
another problem. Why do other people, including experts whose
intelligence and intellectual integrity I respect, think that evidence
of local population fluctuations confirms the hypothesis that
natural selection has the capacity to work engineering marvels, to
construct wonders like the eye and the wing? Everyone who studies
evolution knows that Kettlewell's peppered moth experiment is the
classic demonstration of the power of natural selection, and that
Darwinists had to wait almost a century to see even this modest
confirmation of their central doctrine. Everyone who studies the
experiment also knows that it has nothing to do with the origin of any
species, or even any variety, because dark and white moths were
present throughout the experiment. Only the ratios of one variety to
the other changed. How could intelligent people have been so
gullible as to imagine that the Kettlewell experiment in any way
supported the ambitious claims of Darwinism? To answer that question
we need to consider a fourth way in which natural selection can be
formulated.
NATURAL SELECTION AS A PHILOSOPHICAL NECESSITY
-
The National Academy of Sciences told the Supreme Court that the
most basic characteristic of science is "reliance upon naturalistic
explanations," as opposed to "supernatural means inaccessible to human
understanding." In the latter, unacceptable category contemporary
scientists place not only God, but also any non-material vital force
that supposedly drives evolution in the direction of greater
complexity, consciousness, or whatever. If science is to have any
explanation for biological complexity at all it has to make do with
what is left when the unacceptable has been excluded. Natural
selection is the best of the remaining alternatives, probably the only
alternative.
In this situation some may decide that Darwinism simply must be
true, and for such persons the purpose of any further investigation
will be merely to explain how natural selection works and to solve the
mysteries created by apparent anomalies. For them there is no need
to test the theory itself, for there is no respectable alternative
to test it against. Any persons who say the theory itself is
inadequately supported can be vanquished by the question "Darwin's
Bulldog" T. H. Huxley used to ask the doubters in Darwin's time:
What is your alternative?
I do not think that many scientists would be comfortable accepting
Darwinism solely as a philosophical principle, without seeking to find
at least some empirical evidence that it is true. But there is an
important difference between going to the empirical evidence to test a
doubtful theory against some plausible alternative, and going to the
evidence to look for confirmation of the only theory that one is
willing to tolerate. We have already seen that distinguished
scientists have accepted uncritically the questionable analogy between
natural and artificial selection, and that they have often been
undisturbed by the fallacies of the "tautology" and "deductive
logic" formulations. Such illogic survived and reproduced itself for
the same reason that an apparently incompetent species sometimes
avoids extinction; there was no effective competition in its
ecological niche.
If positive confirmation of the creative potency of natural
selection is not required, there is little danger that the theory will
be disproved by negative evidence. Darwinists have evolved an array of
subsidiary concepts capable of furnishing a plausible explanation
for just about any conceivable eventuality. For example, the living
fossils, which have remained basically unchanged for millions of years
while their cousins were supposedly evolving into more advanced
creatures like human beings, are no embarrassment to Darwinists.
They failed to evolve because the necessary mutations didn't arrive,
or because of "developmental constraints," or because they were
already adequately adapted to their environment. In short, they didn't
evolve because they didn't evolve.
Some animals give warning signals at the approach of predators,
apparently reducing their own safety for the benefit of others in
the herd. How does natural selection encourage the evolution of a
trait for self-sacrifice? Some Darwinists attribute the apparent
anomaly to "group selection." Human nations benefit if they contain
individuals willing to die in battle for their country, and likewise
animal groups containing self-sacrificing individuals may have an
advantage over groups composed exclusively of selfish individuals.
Other Darwinists are scornful of group selection and prefer to
explain altruism on the basis of "kinship selection." By sacrificing
itself to preserve its offspring or near relations an individual
promotes the survival of its genes. Selection may thus operate at
the genetic level to encourage the perpetuation of genetic
combinations that produce individuals capable of altruistic
behavior. By moving the focus of selection either up (to the group
level) or down (to the genetic level), Darwinists can easily account
for traits that seem to contradict the selection hypothesis at the
level of individual organisms.
Potentially the most powerful explanatory tool in the entire
Darwinist armory is pleiotropy, the fact that a single gene has
multiple effects. This means that any mutation which affects one
functional characteristic is likely to change other features as
well, and whether or not it is advantageous depends upon the net
effect. Characteristics which on their face appear to be maladaptive
may therefore be presumed to be linked genetically to more favorable
characteristics, and natural selection can be credited with preserving
the package.
I am not implying that there is anything inherently unreasonable
in invoking pleiotropy, or kinship selection, or developmental
constraints to explain why apparent anomalies are not necessarily
inconsistent with Darwinism. If we assume that Darwinism is
basically true then it is perfectly reasonable to adjust the theory as
necessary to make it conform to the observed facts. The problem is
that the adjusting devices are so flexible that in combination they
make it difficult to conceive of a way to test the claims of Darwinism
empirically. Apparently maladaptive features can be attributed to
pleiotropy, or to our inability to perceive the advantage that may
be there, or when all else fails simply to "chance." Darwin wrote that
"If it could be proved that any part of the structure of any one
species had been formed for the exclusive good of another species,
it would annihilate my theory, for such could not have been produced
through natural selection." But this was the same Darwin who
insisted that he had never claimed that natural selection was the
exclusive mechanism of evolution.
One important subsidiary concept- sexual selection- illustrates
the skill of Darwinists at incorporating recalcitrant examples into
their theory. Sexual selection is a relatively minor component in
Darwinist theory today, but to Darwin it was almost as important as
natural selection itself. (Darwin's second classic, The Descent of
Man, is mainly a treatise on sexual selection.) The most famous
example of sexual selection is the peacock's gaudy fan, which is
obviously an encumbrance when a peacock wants to escape a predator.
The fan is stimulating to peahens, however, and so its possession
increases the peacock's prospects for producing progeny even though it
decreases his life expectancy.
The explanation so far is reasonable, even delightful, but what I
find intriguing is that Darwinists are not troubled by the unfitness
of the peahen's sexual taste. Why would natural selection, which
supposedly formed all birds from lowly predecessors, produce a species
whose females lust for males with life-threatening decorations? The
peahen ought to have developed a preference for males with sharp
talons and mighty wings. Perhaps the taste for fans is associated
genetically with some absolutely vital trait like strong egg shells,
but then why and how did natural selection encourage such an absurd
genetic linkage? Nevertheless, Douglas Futuyma boldly proclaims the
peacock as a problem not for Darwinists but for creationists:
-
Do the creation scientists really suppose their Creator saw fit to
create a bird that couldn't reproduce without six feet of bulky
feathers that make it easy prey for leopards?
-
I don't know what creation-scientists may suppose, but it seems to
me that the peacock and peahen are just the kind of creatures a
whimsical Creator might favor, but that an "uncaring mechanical
process" like natural selection would never permit to develop.
What we are seeing in Futuyma's comment about the peacock is the
debating principle that the best defense is a good offense, but we are
also seeing the influence of philosophical preconception in blinding
an intelligent Darwinist to the existence of a counterexample.
Julian Huxley once wrote that "Improbability is to be expected as a
result of natural selection; and we have the paradox that an
exceedingly high apparent improbability in its products can be taken
as evidence for the high degree of its efficacy." On that basis the
theory has nothing to fear from the evidence.
Natural selection is the most famous element in Darwinism, but it is
not necessarily the most important element. Selection merely preserves
or destroys something that already exists. Mutation has to provide the
favorable innovations before natural selection can retain and
encourage them. That brings us to our next subject, which requires a
separate chapter.
Chapter Three
MUTATIONS GREAT AND SMALL
-
"EVOLUTION" IS A concept broad enough to encompass just about any
alternative to instantaneous creation, and so it is not surprising
that thinkers have speculated about evolution ever since ancient
times. Charles Darwin's unique contribution was to describe a
plausible mechanism by which the necessary transformations could
occur, a mechanism that did not require divine guidance, mysterious
vital forces, or any other causes not presently operating in the
world. Darwin was particularly anxious to avoid the need for any
"saltations"- sudden leaps by which a new type of organism appears
in a single generation. Saltations (or systemic macromutations, as
they are often called today) are believed to be theoretically
impossible by most scientists, and for good reason. Living creatures
are extremely intricate assemblies of interrelated parts, and the
parts themselves are also complex. It is impossible to imagine how the
parts could change in unison as a result of chance mutation.
In a word (Darwin's word), a saltation is equivalent to a miracle.
At the extreme, saltationism is virtually indistinguishable from
special creation. If a snake's egg were to hatch and a mouse emerge,
we could with equal justice classify the event as an instance of
evolution or creation. Even the sudden appearance of a single
complex organ, like an eye or wing, would imply supernatural
intervention. Darwin emphatically rejected any evolutionary theory
of this sort, writing to Charles Lyell that
-
If I were convinced that I required such additions to the theory
of natural selection, I would reject it as rubbish.... I would give
nothing for the theory of natural selection, if it requires miraculous
additions at any one stage of descent.
-
Darwin aimed to do for biology what Lyell had done for geology:
explain great changes on uniformitarian and naturalistic principles,
meaning the gradual operation over long periods of time of familiar
natural forces that we can still see operating in the present. He
understood that the distinctive feature of his theory was its
uncompromising philosophical materialism, which made it truly
scientific in the sense that it did not invoke any mystical or
supernatural forces that are inaccessible to scientific investigation.
To achieve a fully materialistic theory Darwin had to explain every
complex characteristic or major transformation as the cumulative
product of a great many tiny steps. In his own eloquent words:
-
Natural selection can act only by the preservation and
accumulation of infinitesimally small inherited modifications, each
profitable to the preserved being; and as modern geology has almost
banished such views as the excavation of a great valley by a single
diluvial wave, so will natural selection, if it be a true principle,
banish the belief of the continued creation of new organic beings,
or of any great and sudden modification in their structure.
-
T. H. Huxley protested against this dogmatic gradualism from the
start, warning Darwin in a famous letter that "You have loaded
yourself with an unnecessary difficulty in adopting natura nonfacit
saltum so unreservedly." The difficulty was hardly unnecessary,
given Darwin's purpose, but it was real enough. In the long term the
biggest problem was the fossil record, which did not provide
evidence of the many transitional forms that Darwin's theory
required to have existed. Darwin made the obvious response, arguing
that the evidence was lacking because the fossil record was
incomplete. This was a reasonable possibility at the time, and
conveniently safe from disproof; we shall return to it in the next
chapter.
The more pressing difficulty was theoretical. Many organs require an
intricate combination of complex parts to perform their functions. The
eye and the wing are the most common illustrations, but it would be
misleading to give the impression that either is a special case; human
and animal bodies are literally packed with similar marvels. How can
such things be built up by "infinitesimally small inherited
variations, each profitable to the preserved being?" The first step
towards a new function- such as vision or ability to fly- would not
necessarily provide any advantage unless the other parts required
for the function appeared at the same time. As an analogy, imagine a
medieval alchemist producing by chance a silicon microchip; in the
absence of a supporting computer technology the prodigious invention
would be useless and he would throw it away.
Stephen Jay Gould asked himself "the excellent question, What good
is 5 per cent of an eye?," and speculated that the first eye parts
might have been useful for something other than sight. Richard Dawkins
responded that
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An ancient animal with 5 per cent of an eye might indeed have used
it for something other than sight, but it seems to me as likely that
it used it for 5 per cent vision. And actually I don't think it is
an excellent question. Vision that is 5 per cent as good as yours or
mine is very much worth having in comparison with no vision at all. So
is 1 per cent vision better than total blindness. And 6 per cent is
better than 5, 7 per cent better than 6, and so on up the gradual,
continuous series.
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The fallacy in that argument is that "5 per cent of an eye" is not
the same thing as "5 per cent of normal vision." For an animal to have
any useful vision at all, many complex parts must be working together.
Even a complete eye is useless unless it belongs to a creature with
the mental and neural capacity to make use of the information by doing
something that furthers survival or reproduction. What we have to
imagine is a chance mutation that provides this complex capacity all
at once, at a level of utility sufficient to give the creature an
advantage in producing offspring.
Dawkins went on to restate Darwin's answer to the eye conundrum,
pointing out that there is a plausible series of intermediate
eye-designs among living animals. Some single-celled animals have a
light-sensitive spot with a little pigment screen behind it, and in
some many-celled animals a similar arrangement is set in a cup,
which gives improved direction-finding capability. The ancient
nautilus has a pinhole eye with no lens, the squid's eye adds the
lens, and so on. None of these different types of eyes are thought
to have evolved from any of the others, however, because they
involve different types of structures rather than a series of
similar structures growing in complexity.
If the eye evolved at all, it evolved many times. Ernst Mayr
writes that the eye must have evolved independently at least 40 times,
a circumstance which suggests to him that "a highly complicated
organ can evolve repeatedly and convergently when advantageous,
provided such evolution is at all probable." But then why did the many
primitive eye forms that are still with us never evolve into more
advanced forms? Dawkins admits to being baffled by the nautilus, which
in its hundreds of millions of years of existence has never evolved
a lens for its eye despite having a retina that is "practically crying
out for (this) particular simple change." *
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* Before leaving the subject of the eye, I should add that
Darwinists cite imperfections in the eye as evidence that it was not
designed by an omniscient creator. According to Dawkins, the
photocells are "wired backwards," and "any tidy-minded engineer" would
not have been so sloppy.
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The wing, which exists in quite distinct forms in insects, birds,
and bats, is the other most frequently cited puzzle. Would the first
"infinitesimally small inherited modification" in the direction of
wing construction confer a selective advantage? Dawkins thinks that it
would, because even a small flap or web might help a small creature to
jump farther, or save it from breaking its neck in a fall.
Eventually such a proto-wing might develop to a point where the
creature would begin gliding, and by further gradual improvements it
would become capable of genuine flight. What this imaginative scenario
neglects is that forelimbs evolving into wings would probably become
awkward for climbing or grasping long before they became very useful
for gliding, thus placing the hypothetical intermediate creature at
a serious disadvantage.
There is a good skeptical discussion of the bird wing problem in
chapter 9 of Denton's Evolution: A Theory in Crisis. Denton
describes the exquisitely functional avian feather, with its
interlocking hooks and other intricate features that make it
suitable for flight and quite distinct from any form of feather used
only for warmth. Bird feathers must have evolved from reptilian scales
if Darwinism is true, but once again the intermediates are hard to
imagine. Still more difficult a problem is presented by the
distinctive avian lung, which is quite different in structure than
that of any conceivable evolutionary ancestor. According to Denton,
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Just how such a different respiratory system could have evolved
gradually from the standard vertebrate design is fantastically
difficult to envisage, especially bearing in mind that the maintenance
of respiratory function is absolutely vital to the life of an organism
to the extent that the slightest malfunction leads to death within
minutes. Just as the feather cannot function as an organ of flight
until the hooks and barbules are coadapted to fit together
perfectly, so the avian lung cannot function as an organ of
respiration until the parabronchi system which permeates it and the
air sac system which guarantees the parabronchi their air supply are
both highly developed and able to function together in a perfectly
integrated manner.
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Whether one finds the gradualist scenarios for the development of
complex systems plausible involves an element of subjective
judgment. It is a matter of objective fact, however, that these
scenarios are speculation. Bird and bat wings appear in the fossil
record already developed, and no one has ever confirmed by
experiment that the gradual evolution of wings and eyes is possible.
This absence of historical or experimental confirmation is
presumably what Gould had in mind when he wrote that "These tales,
in the 'just-so' tradition of evolutionary natural history, do not
prove anything." Are we dealing here with science or with
rationalist versions of Kipling's fables?
Darwin wrote that "If it could be demonstrated that any complex
organ existed which could not possibly have been formed by numerous,
successive, slight modifications, my theory would absolutely break
down." One particularly eminent scientist of the mid-twentieth century
who concluded that it had absolutely broken down was the
German-American geneticist, Professor Richard Goldschmidt of the
University of California at Berkeley. Goldschmidt issued a famous
challenge to the neo-Darwinists, listing a series of complex
structures from mammalian hair to hemoglobin that he thought could not
have been produced by the accumulation and selection of small
mutations. Like Pierre Grasse, Goldschmidt concluded that Darwinian
evolution could account for no more than variations within the species
boundary; unlike Grasse, he thought that evolution beyond that point
must have occurred in single jumps through macromutations. He conceded
that large-scale mutations would in almost all cases produce
hopelessly maladapted monsters, but he thought that on rare
occasions a lucky accident might produce a "hopeful monster," a member
of a new species with the capacity to survive and propagate (but
with what mate?).
The Darwinists met this fantastic suggestion with savage ridicule.
As Goldschmidt put it, "This time I was not only crazy but almost a
criminal." Gould has even compared the treatment accorded
Goldschmidt in Darwinist circles with the daily "Two Minute Hate"
directed at "Emmanuel Goldstein, enemy of the people" in George
Orwell's novel 1984. The venom is explained by the emotional
attachment Darwinists have to their theory, but the ridicule had a
sound scientific basis. If Goldschmidt really meant that all the
complex interrelated parts of an animal could be reformed together
in a single generation by a systemic macromutation, he was postulating
a virtual miracle that had no basis either in genetic theory or in
experimental evidence. Mutations are thought to stem from random
errors in copying the commands of the DNA's genetic code. To suppose
that such a random event could reconstruct even a single complex organ
like a liver or kidney is about as reasonable as to suppose that an
improved watch can be designed by throwing an old one against a
wall. Adaptive macromutations are impossible, say the Darwinists,
especially if required in any quantity, and so all those complex
organs must have evolved- many times independently- by the selective
accumulation of micromutations over a long period of time.
But now we must deal with another fallacy, and a supremely important
one. That evolution by macromutation is impossible does not prove that
evolution by micromutation is probable, or even possible. It is likely
that Darwinist gradualism is statistically just as unlikely as
Goldschmidt's saltationism, once we give adequate attention to all the
necessary elements. The advantageous micromutations postulated by
neo-Darwinist genetics are tiny, usually too small to be noticed. This
premise is important because, in the words of Richard Dawkins,
"virtually all the mutations studied in genetics laboratories- which
are pretty macro because otherwise geneticists wouldn't notice them-
are deleterious to the animals possessing them." But if the
necessary mutations are too small to be seen, there will have to be
a great many of them (millions?) of the right type coming along when
they are needed to carry on the long-term project of producing a
complex organ.
The probability of Darwinist evolution depends upon the quantity
of favorable micromutations required to create complex organs and
organisms, the frequency with which such favorable micromutations
occur just where and when they are needed, the efficacy of natural
selection in preserving the slight improvements with sufficient
consistency to permit the benefits to accumulate, and the time allowed
by the fossil record for all this to have happened. Unless we can make
calculations taking all these factors into account, we have no way
of knowing whether evolution by micromutation is more or less
improbable than evolution by macromutation.
Some mathematicians did try to make the calculations, and the result
was a rather acrimonious confrontation between themselves and some
of the leading Darwinists at the Wistar Institute in Philadelphia in
1967. The report of the exchange is fascinating, not just because of
the substance of the mathematical challenge, but even more because
of the logic of the Darwinist response. For example, the mathematician
D. S. Ulam argued that it was highly improbable that the eye could
have evolved by the accumulation of small mutations, because the
number of mutations would have to be so large and the time available
was not nearly long enough for them to appear. Sir Peter Medawar and
C. H. Waddington responded that Ulam was doing his science
backwards; the fact was that the eye had evolved and therefore the
mathematical difficulties must be only apparent. Ernst Mayr observed
that Ulam's calculations were based on assumptions that might be
unfounded, and concluded that "Somehow or other by adjusting these
figures we will come out all right. We are comforted by the fact
that evolution has occurred."
The Darwinists were trying to be reasonable, but it was as if Ulam
had presented equations proving that gravity is too weak a force to
prevent us all from floating off into space. Darwinism to them was not
a theory open to refutation but a fact to be accounted for, at least
until the mathematicians could produce an acceptable alternative.
The discussion became particularly heated after a French mathematician
named Schutzenberger concluded that "there is a considerable gap in
the neo-Darwinian theory of evolution, and we believe this gap to be
of such a nature that it cannot be bridged within the current
conception of biology." C. H. Waddington thought he saw where this
reasoning was headed, and retorted that "Your argument is simply
that life must have come about by special creation." Schutzenberger
(and anonymous voices from the audience) shouted "No!," but in fact
the mathematicians did not present an alternative.
The difficulties with both the micromutational and macromutational
theories are so great that we might expect to see some effort being
made to come up with a middle ground that minimizes the
disadvantages of both extremes. Stephen Jay Gould attempted
something of the sort, both in his 1980 scientific paper proposing a
"new and general theory," and in his popular article "The Return of
the Hopeful Monster." Gould tried to rehabilitate Goldschmidt while
domesticating his monster. Goldschmidt did not really mean that "new
species arise all at once, fully formed, by a fortunate
macromutation," Gould explained, and what he did mean can be
reconciled with "the essence of Darwinism."
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Suppose that a discontinuous change in adult form arises from a
small genetic alteration. Problems of discordance with other members
of the species do not arise, and the large, favorable variant can
spread through a population in Darwinian fashion. Suppose also that
this large change does not produce a perfected form all at once, but
rather serves as a "key" adaptation to shift its possessor toward a
new mode of life. Continued success in this new mode may require a
large set of collateral alterations, morphological and behavioral;
these may arise by a more traditional, gradual route once the key
adaptation forces a profound shift in selective pressures.
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We have to do all this supposing, according to Gould, because it
is just too hard to "invent a reasonable sequence of intermediate
forms- that is, viable, functioning organisms- between ancestors and
descendants in major structural transitions." In the end we will
have to accept "many cases of discontinuous transition in
macroevolution." The kind of small genetic alteration which Gould
had in mind (and said Goldschmidt had in mind) was a mutation in the
genes regulating embryonic development, on the theory that "small
changes early in embryology accumulate through growth to yield
profound differences among adults." Indeed they must do so, because
otherwise Gould could not see any way that major evolutionary
transitions could have been accomplished.
Gould published a major article in the scientific journal
Paleobiology which expressed his endorsement of Goldschmidt even
more explicitly, and in which he pronounced the effective death of the
neo-Darwinian synthesis. In place of the dead orthodoxy he hailed as
"the epitome and foundation of emerging views on speciation" a passage
by Goldschmidt which insisted that "neo-Darwinian evolution... is a
process which leads to diversification strictly within the species.
... The decisive step in evolution, the first step towards
macroevolution, the step from one species to another, requires another
evolutionary method than the sheer accumulation of micromutations."
With respect to the evolution of complex organs, Gould disavowed
reliance on "saltational origin of entire new designs," but proposed
instead "a potential saltational origin for the essential features
of key adaptations." In short, he tried to split the difference
between Darwinism and Goldschmidtism.
And so the hopeful monster returned, but its hopes were soon
disappointed once again. Ernst Mayr, the most prestigious of living
neo-Darwinists, wrote that Gould had entirely misrepresented
Goldschmidt's theory in denying that Goldschmidt advocated impossible,
single-generation systemic macromutations. "Actually, this is what
Goldschmidt repeatedly claimed. For instance, he cited with approval
Schindewolf's * suggestion that the first bird hatched out of a
reptilian egg...." Mayr thought that some mutations with large scale
effects might be possible, *(2) but he could find no evidence that any
great number of them had occurred and he saw no need to invoke them
because he considered the mechanisms of neo-Darwinism capable of
explaining the emergence of evolutionary novelties.
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* Otto Schindewolf was a prominent paleontologist whom we will
encounter again in the next chapter.
*(2) The debate over macromutations has mainly concerned the
animal kingdom, but it is well known that a special kind of
macromutation, known as polyploidy, can produce new plant species.
This phenomenon, which involves the doubling of chromosome numbers
in cell division applies only to hermaphrodite species capable of
self-fertilization. As a result it is important only for plants,
although not entirely absent from the animal kingdom. In any case,
polyploidy would not explain the creation of complex adaptive
structures like wings and eyes.
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Richard Dawkins wrote scornfully of Goldschmidt in The Blind
Watchmaker, and criticized Gould for trying to rehabilitate him. For
Dawkins, "Goldschmidt's problem... turns out to be no problem at all,"
because there is no real difficulty in accounting for the
development of complex structures by gradualistic evolution. What
Dawkins seems to mean by this assertion is that the step-by-step
evolution of complex adaptive systems is a conceptual possibility, not
that there is some way to prove that it actually happens. He uses
the bat, with its marvelous sonar-like echolocation system that so
resembles the product of an advanced technological society, as the
paradigm example of how natural selection can explain the
development of a complex system that would otherwise be taken as
evidence for the existence of a "watchmaker" creator. Dawkins is right
to argue that if Darwinist evolution can craft a bat it can make
just about anything, but what he neglects to do is to prove that
Darwinist evolution can do anything of the kind. It is conceivable
that bat sonar evolved by some step-by-step process, in which the
first hint of an ability to locate by echo was of such value to its
possessor that everything else had to follow, but how do we know
that such a thing ever happened, or could have happened?
Despite his generally rigid adherence to Darwinist gradualism,
even Dawkins finds it impossible to get along without what might be
called modest macromutations, meaning mutations that "although they
may be large in the magnitude of their effects, turn out not to be
large in terms of their complexity." He uses as an example snakes,
some contemporary examples of which have more vertebrae than their
presumed ancestors. The number of vertebrae has to be changed in whole
units, and to accomplish this "you need to do more than just shove
in an extra bone," because each vertebra has associated with it a
set of nerves, blood vessels, muscles, and so on. These complicated
parts would all have to appear together for the extra vertebrae to
make any biological sense, but "it is easy to believe that
individual snakes with half a dozen more vertebrae than their
parents could have arisen in a single mutational step." This is easy
to believe, according to Dawkins, because the mutation only adds
more of what was already there, and because the change only appears to
be macromutational when we look at the adult. At the embryonic
level, such changes "turn out to be micromutations, in the sense
that only a small change in the embryonic instructions had a large
apparent effect in the adult."
Gould supposes what he has to suppose, and Dawkins finds it easy
to believe what he wants to believe, but supposing and believing are
not enough to make a scientific explanation. Is there any way to
confirm the hypothesis that mutations in the genes which regulate
embryonic development might provide whatever is needed to get
evolution over the unbridgeable gaps? Creatures that look very
different as adults are sometimes much more alike at the early
embryonic stages, and so there is a certain plausibility to the notion
that a simple but basic change in the genetic program regulating
development could induce an embryo to develop in an unusual direction.
In principle, this is the kind of change we might imagine human
genetic engineers to be capable of directing one day, if this branch
of science continues to advance in the future as it has in the
recent past.
Suppose that, following a massive research program, scientists
succeed in altering the genetic program of a fish embryo so that it
develops as an amphibian. Would this hypothetical triumph of genetic
engineering confirm that amphibians actually evolved, or at least
could have evolved, in similar fashion?
No it wouldn't, because Gould and the others who postulate
developmental macromutations are talking about random changes, not
changes elaborately planned by human (or divine) intelligence. A
random change in the program governing my word processor could
easily transform this chapter into unintelligible gibberish, but it
would not translate the chapter into a foreign language, or produce
a coherent chapter about something else. What the proponents of
developmental macromutations need to establish is not merely that
there is an alterable genetic program governing development, but
that important evolutionary innovations can be produced by random
changes in the genetic instructions.
The prevailing assumption in evolutionary science seems to be that
speculative possibilities, without experimental confirmation, are
all that is really necessary. The principle at work is the same one
that Waddington, Medawar, and Mayr invoked when challenged by the
mathematicians. Nature must have provided whatever evolution had to
have, because otherwise evolution wouldn't have happened. It follows
that if evolution required macromutations then macromutations must
be possible, or if macromutations are impossible then evolution must
not have required them. The theory itself provides whatever supporting
evidence is essential.
If the Darwinists are at all uncomfortable with this situation
(actually, most of them don't seem to be), the anti-Darwinists are
in no better shape. The great geneticist Goldschmidt was reduced to
endorsing a genetic impossibility, and the great zoologist Grasse
could do no better than to suggest that evolving species somehow
acquire a new store of genetic information due to obscure "internal
factors" involving "a phenomenon whose equivalent cannot be seen in
the creatures living at the present time (either because it is not
there or because we are unable to see it)." Grasse was all too aware
that such talk "arouses the suspicions of many biologists... [because]
it conjures up visions of the ghost of vitalism or of some mystical
power which guides the destiny of living things...." He repeatedly
denied that he had anything of the sort in mind, but suspicions of
vitalism once aroused are not conjured away by bare denials.
We can see from these examples why neo-Darwinism retains its
status as textbook orthodoxy despite all the difficulties and even the
imputations of moribundity. If neo-Darwinist gradualism were abandoned
as incapable of explaining macroevolutionary leaps and the origin of
complex organs, most biologists would still believe in evolution
(Goldschmidt and Grasse never doubted that evolution had occurred),
but they would have no theory of evolution. Materialist scientists are
full of scorn for creationists who invoke an invisible creator who
employed supernatural powers that cannot be observed operating in
our own times. If evolutionary science must also rely upon mystical
guiding forces or upon genetically impossible transformations, a
philosophical materialist like Charles Darwin would call it rubbish.
Until now I have avoided discussing the fossil evidence in order
to concentrate on the theoretical and experimental difficulties that
surround the reigning neo-Darwinist synthesis. But evolution is at
bottom about history; it aims to tell us what happened in the past. On
that subject the fossils are our most direct evidence, and it is to
them that we turn next.
Chapter Four
THE FOSSIL PROBLEM
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TODAY IT IS widely assumed that the existence of fossil remains of
numerous extinct species necessarily implies evolution, and most
people are unaware that Darwin's most formidable opponents were not
clergymen, but fossil experts. In the early nineteenth century the
prevailing geological theory was the "catastrophism" advocated by
the great French scientist Cuvier, the father of paleontology.
Cuvier believed that the geological record showed a pattern of
catastrophic events involving mass extinctions, which were followed by
periods of creation in which new forms of life appeared without any
trace of evolutionary development.
In Darwin's time, Cuvier's catastrophism was being supplanted by the
uniformitarian geology advocated by Darwin's older friend Charles
Lyell, who explained spectacular natural features as the result not of
sudden cataclysms, but rather the slow working over immense time of
everyday forces. In retrospect, an evolutionary theory of the
Darwinian kind seems almost an inevitable extension of Lyell's
logic, but Lyell himself had great difficulty accepting biological
evolution, as did many other persons who were familiar with the
evidence.
Each of the divisions of the biological world (kingdoms, phyla,
classes, orders), it was noted, conformed to a basic structural
plan, with very few intermediate types. Where were the links between
these discontinuous groups? The absence of transitional
intermediates was troubling even to Darwin's loyal supporter T. H.
Huxley, who warned Darwin repeatedly in private that a theory
consistent with the evidence would have to allow for some big jumps.
Darwin posed the question himself, asking
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why, if species have descended from other species by insensibly fine
gradations, do we not everywhere see innumerable transitional forms?
Why is not all nature in confusion instead of the species being, as we
see them, well defined?
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He answered with a theory of extinction which was the logical
counterpart of "the survival of the fittest." The appearance of an
improved form implies a disadvantage for its parent form. Thus, "if we
look at each species as descended from some other unknown form, both
the parent and all the transitional varieties will generally have been
exterminated by the very process of formation and perfection of the
new form." This extermination-by-obsolescence implies that appearances
will be against a theory of evolution in our living world, because
we see distinct, stable species (and larger groupings), with only rare
intermediate forms. The links between the discontinuous groups that
once existed have vanished due to maladaptation.
But what if the necessary links are missing not only from the
world of the present, but from the fossil record of the past as
well? Darwin acknowledged that his theory implied that "the number
of intermediate and transitional links, between all living and extinct
species, must have been inconceivably great." One might therefore
suppose that geologists would be continually uncovering fossil
evidence of transitional forms. This, however, was clearly not the
case. What geologists did discover was species, and groups of species,
which appeared suddenly rather than at the end of a chain of
evolutionary links. Darwin conceded that the state of the fossil
evidence was "the most obvious and gravest objection which can be
urged against my theory," and that it accounted for the fact that "all
the most eminent paleontologists... and all our greatest geologists...
have unanimously, often vehemently, maintained the immutability of
species."
Darwin argued eloquently that the fossil problem, although
concededly serious, was not fatal to his theory. His main point was
that the fossil record is extremely imperfect. Fossils are preserved
only in special circumstances, and thus the various fossil beds of the
world probably reflect not a continuous record but rather pictures
of relatively brief periods separated from each other by wide
intervals of time. Additionally, we might fail to recognize
ancestor-descendant relationships in the fossils even if they were
present. Unless we had all the intervening links to show the
connections between them, the two forms might appear entirely distinct
to our eyes. At times Darwin even seemed to be implying that the
absence of transitionals was itself a proof of the inadequacy of the
record, as it would be if one had a priori knowledge that his theory
was true:
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I do not pretend that I should ever have suspected how poor a record
of the mutations of life, the best preserved geological section
presented, had not the difficulty of our not discovering innumerable
transitional links between the species which appeared at the
commencement and close of each formation, pressed so hardly on my
theory.
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Darwin did as well with the fossil problem as the discouraging facts
allowed, but to some questions he had to respond frankly that "I can
give no satisfactory answer," and there is a hint of desperation in
his writing at times, as in the following sentence: "Nature may almost
be said to have guarded against the frequent discovery of her
transitional or linking forms." But Darwin never lost faith in his
theory; the only puzzle was how to account for the plainly
misleading aspects of the fossil record.
At this point I ask the reader to stop with me for a moment and
consider what an unbiased person ought to have thought about the
controversy over evolution in the period immediately following the
publication of The Origin of Species. Opposition to Darwin's theory
could hardly be attributed to religious prejudice when the skeptics
included the leading paleontologists and geologists of the day.
Darwin's defense of the theory against the fossil evidence was not
unreasonable, but the point is, it was a defense. Very possibly the
fossil beds are mere snapshots of moments in geological time, with
sufficient time and space between them for a lot of evolution to be
going on in the gaps. Still, it is one thing to say that there are
gaps, and quite another thing to claim the right to fill the gaps with
the evidence required to support one's theory. Darwin's arguments
could establish at most that the fossil problem was not fatal; they
could not turn the absence of confirming evidence into an asset.
There was a way to test the theory by fossil evidence, however, if
Darwin and his followers had wanted a test. Darwin was emphatic that
the number of transitional intermediates must have been immense,
even "inconceivable." Perhaps evidence of their existence was
missing because in 1859 only a small part of the world's fossil beds
had been searched, and because the explorers had not known what to
look for. Once paleontologists accepted Darwinism as a working
hypothesis, however, and explored many new fossil beds in an effort to
confirm the theory, this situation ought to change. In time the fossil
record could be expected to look very different, and very much more
Darwinian.
The test would not be fair to the skeptics, however, unless it was
also possible for the theory to fail. Imagine, for example, that
belief in Darwin's theory were to sweep through the scientific world
with such irresistible power that it very quickly became an orthodoxy.
Suppose that the tide was so irresistible that even the most
prestigious of scientists- Harvard's Louis Agassiz, for example-
became an instant has-been for failing to join the movement. Suppose
that paleontologists became so committed to the new way of thinking
that fossil studies were published only if they supported the
theory, and were discarded as failures if they showed an absence of
evolutionary change. As we shall see, that is what happened. Darwinism
apparently passed the fossil test, but only because it was not allowed
to fail.
Darwin's theory predicted not merely that fossil transitionals would
be found; it implied that a truly complete fossil record would be
mostly transitionals, and that what we think of as fixed species would
be revealed as mere arbitrary viewpoints in a process of continual
change. Darwinism also implied an important prediction about
extinction, that necessary corollary of the struggle for existence.
Darwin recognized that his theory required a pattern of extinction
even more gradual than the pattern of evolutionary emergence:
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The old notion of all the inhabitants of the earth having been swept
away at successive periods by catastrophes, is very generally given
up, even by those geologists... whose general views would naturally
lead them to this conclusion.... There is reason to believe that the
complete extinction of the species of a group is generally a slower
process than their production: if the appearance and disappearance
of a group of species be represented, as before, by a vertical line of
varying thickness, the line is found to taper more gradually at its
upper end, which marks the progress of extermination, than in its
lower end, which marks the first appearance and increase in numbers of
the species. In some cases, however, the extermination of whole groups
of beings, as of ammonites towards the close of the secondary
period, has been wonderfully sudden.
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Continual, gradual extinctions are a necessary consequence of the
assumption that ancestor species are constantly being supplanted by
better adapted descendants. Suppose, however, that it were shown
that a substantial proportion of extinctions have occurred in the
course of a few global catastrophes, such as might be caused by a
comet hitting the earth or some sudden change in temperature. In
such catastrophes survival would not necessarily have been related
to fitness in more normal circumstances, and might have been
entirely at random. Darwinism could therefore be tested not only by
searching for transitional species in newly discovered fossil beds,
but also by studying the pattern of extinctions to measure the
importance of catastrophes.
Evolution triumphed during Darwin's lifetime, although his
opposition to saltations remained controversial in scientific
circles for a long time to come. The discovery of Archaeopteryx- an
ancient bird with some strikingly reptilian features- was enough
fossil confirmation in itself to satisfy many. Thereafter it was one
apparent fossil success after another, with reports of human
ancestors, ancient mammal-like reptiles, a good sequence in the
horse line, and so on. Paleontology joined the neo-Darwinian synthesis
in the work of George Gaylord Simpson, who declared that Darwin had
been confirmed by the fossils (a declaration that was communicated
to generations of biology students as fact). What Stephen Jay Gould
described in 1980 as "the most sophisticated of modern American
textbooks for introductory biology" endorsed the synthetic theory on
the basis of fossil evidence:
-
[Can] more extensive evolutionary change, macroevolution, be
explained as an outcome of these microevolutionary shifts? Did birds
really arise from reptiles by an accumulation of gene substitutions of
the kind illustrated by the raspberry eye-color gene?
The answer is that it is entirely plausible, and no one has come
up with a better explanation.... The fossil record suggests that
macroevolution is indeed gradual, paced at a rate that leads to the
conclusion that it is based on hundreds or thousands of gene
substitutions no different in kind from the ones examined in our
case histories.
-
But that last sentence is false, and has long been known to
paleontologists to be false.
The fossil record was revisited in the 1970s in works by Stephen Jay
Gould, Niles Eldredge, and Steven Stanley. Gould and Eldredge proposed
a new theory they called "punctuated equilibrium" ("punk eek" to the
irreverent), to deal with an embarrassing fact: the fossil record
today on the whole looks very much as it did in 1859, despite the fact
that an enormous amount of fossil hunting has gone on in the
intervening years. In the words of Gould:
-
The history of most fossil species includes two features
particularly inconsistent with gradualism:
-
1. Stasis. Most species exhibit no directional change during their
tenure on earth. They appear in the fossil record looking pretty
much the same as when they disappear; morphological change is
usually limited and directionless.
2. Sudden appearance. In any local area, a species does not
arise gr |
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