Download natural selections

Natural Selections
By David Papineau, The New York Times
May 14, 1995
Reinventing Darwin: The Great Debate at the High Table of Evolutionary Theory. By
Niles Eldredge. Illustrated. 244 pp. New York: John Wiley & Sons. $27.95. River Out of
Eden: A Darwinian View of Life. By Richard Dawkins. Illustrated. 172 pp. New York:
Basic Books. $20. Darwin's Dangerous Idea: Evolution and the Meanings of Life. By
Daniel C. Dennett. Illustrated. 586 pp. New York: Simon & Schuster. $30.
CHARLES DARWIN has been in the headlines for well over a century. Ever since his
theory of evolution by natural selection was first published in 1859, scientific discussion
of its validity has spilled over into heated public debate. The details under dispute have
varied, but the underlying question has remained the same: Can natural selection fully
account for the architecture of living forms, or are there biological phenomena beyond its
scope?
It is not hard to see why the question should cause so much ferment. Darwin's theory
ascribes purposes, in a sense, to our bodily parts. It explains our eyes in terms of the
contribution eyes have made to the survival of humans. But when it comes to the
purpose of humans themselves, or of the mechanism of natural selection that made
them, the theory says nothing.
If Darwin is right, we have been sired by blind chance out of the laws of physics. We
testify to nothing but the fact that matter will arrange itself into strange configurations if
left alone for long enough. So it is scarcely surprising that Darwin's theory should have
been so closely scrutinized. If only we can find something in the biological world that
Darwin cannot explain, perhaps life will have a meaning after all.
The desire to escape Darwin is a common theme in contemporary thought. Its spreads
far beyond creationist circles into the strongholds of secular rationalism. Stephen Jay
Gould, a professor of geology and zoology at Harvard University, has long argued that
many aspects of the biological world cannot be understood in terms of natural selection.
Noam Chomsky, down the road at the Massachusetts Institute of Technology, is
skeptical of any Darwinian explanation for language, despite his long campaign to
establish that our linguistic faculty is biologically innate. The philosopher Jerry Fodor, for
many years Mr. Chomsky's colleague, is a leading proponent of the materialist approach
to the mind; yet he resists any attempt to understand our cognitive workings in terms of
natural selection.
To official Darwinians this kind of secular skepticism is almost worse than creationism. It
is bad enough that people who believe the Bible literally should dismiss Darwin. But
members of the scientific community ought to know better. Darwinians admit that
theorists like Mr. Gould raise serious scientific points, but they feel it only raises false
hopes to present these as undermining Darwinism. To do so suggests that life has more
meaning than Darwin allows, when in fact the skeptics know that their own arguments
show nothing of the sort.
Two decades ago Niles Eldredge wrote a famous article with Stephen Jay Gould,
entitled "Punctuated Equilibria," which challenged various aspects of Darwinian
orthodoxy. In "Reinventing Darwin" he now aims to bring the general reader up to date
with the ensuing debate between those he calls the "ultra-Darwinians," like the British
biologist Richard Dawkins, and the "naturalists," like Mr. Gould and himself.
"Reinventing Darwin" is lively and well written. But attentive readers might end up
wondering why Mr. Eldredge, a curator in the department of invertebrates at the
American Museum of Natural History, is at such pains to distance himself from the ultraDarwinians. An initial objection he raises is that Darwinians are "adaptationists" who
think that every biological trait has been designed by natural selection for some purpose.
But in reality, he argues, many traits are nothing but side effects of other design choices.
This is the point of a well-known parable, written by Mr. Gould and the Harvard biologist
Richard Lewontin, about the spandrels of San Marco. These spandrels are triangular
panels in the ceiling of St. Mark's in Venice. As a casual tourist, you might come up with
various theories about why the architects chose just this design. However, your theories
would be wrong. The architects had no choice about it. Any dome supported by circular
arches, as is the dome of St. Mark's, must have spandrels for structural reasons. As in
architecture, so in biology. If you want to know why insects are all so small, you are
barking up the wrong tree, for their size is an inevitable result of their lack of bony
skeletons.
This point is true enough, but it lacks dialectical force. Most self-confessed Darwinians
nowadays simply concede the issue, as Mr. Eldredge acknowledges. They allow that
many traits, like the small size of insects, have no purpose. They insist only that when
there is purpose, it is due to natural selection. And Mr. Eldredge in turn agrees to this.
He makes it clear that he does not believe in any higher agency, and that common
natural selection is the only source of design in nature.
If all this is agreed, what is the fuss about? If subsidiary traits were designed by
something, that would be news. But naturalists like Mr. Eldredge agree they aren't
designed at all. They are just spandrels, side effects of other traits. Ultra-Darwinians can
retort, with some justice, that they never denied the existence of spandrels. They just
thought them too obvious to mention.
The controversy about "punctuated equilibrium" is similarly puzzling. Mr. Eldredge and
Mr. Gould point out that natural selection seems to operate as an active designer in only
a small part of evolutionary history. Most of the time species remain in "equilibrium,"
doing what they have always done. It is only when this stasis is "punctuated" by the
fortuitous isolation of new proto-species that natural selection has the power to design
anything. But most official Darwinians are happy to concede this too. They accept that
natural selection probably operates relatively infrequently. But, they point out, that
doesn't mean something else is designing nature instead. Nor, of course, does Mr.
Eldredge claim that. When the designing gets done, it is always natural selection that
does it.
SOME of Mr. Eldredge's other attempts to distance himself from the Darwinians are
more metaphorical. For example, he says that ultra-Darwinians think of natural selection
as an active force driven by reproductive competition, whereas in truth it is merely a
"filter" that preserves the genes of successful organisms. Given this, it is somewhat
surprising to find the leading ultra-Darwinist Richard Dawkins saying on page 3 of his
new book "River Out of Eden": "Each generation is a filter, a sieve: good genes tend to
fall through the sieve into the next generation."
2
Mr. Dawkins is often portrayed as the village reductionist, the man who thinks there is
nothing to life but selfish genes. But this is less than fair. He is often polemical and
always combative. His first book, "The Selfish Gene" (1976), cut some argumentative
corners in the service of a good story. But readers of his later works, "The Extended
Phenotype" (1982) and "The Blind Watchmaker" (1986), will know that he is a careful
thinker, prepared to qualify his position when necessary. Ultra-Darwinian he may be, but
he is not blind to the issues that concern naturalists like Mr. Eldredge; in many cases he
has simply absorbed their good points into his overall Darwinian perspective.
He is above all a masterly expositor, a writer who understands the issues so clearly that
he forces his readers to understand them too. "River Out of Eden" displays these virtues
to the full. It is a thinner book than his others, with no special message to deliver, but it
maintains his high standards of clarity and excitement. The "river" of the title is the river
of DNA that flows from early life forms to their present-day descendants. This is a
powerful metaphor, and Mr. Dawkins puts it to a number of good uses. In particular,
anybody who has been confused by the recent "African Eve" controversy about the
origin of modern humans will be relieved to find the issues laid bare here.
Daniel C. Dennett, Distinguished Arts and Sciences Professor at Tufts University, is a
new recruit to the ranks of public ultra-Darwinians. He is a philosopher whose work has
always been informed by implicit Darwinian assumptions, but until now he has felt little
need to defend them. Recently, however, he has found that his appeals to Darwin are
often resisted on the authority of Mr. Gould, Mr. Chomsky or Mr. Fodor. His patience
with his colleagues in the Boston area has finally snapped. The result is "Darwin's
Dangerous Idea: Evolution and the Meanings of Life," a 586-page volume designed to
close down all opposition to Darwinism.
David Papineau's most recent book is "Philosophical Naturalism."
3