The Deniable Darwin
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Author: David Berlinski
COMMENTARY, VOL. 101, June 1996 No. 6
The fossil record is incomplete, the reasoning flawed; is the theory of evolution fit to survive?
[DAVID BERLINSKI, who has taught mathematics and philosophy in American and French universities, is the author, most recently, of A Tour of the Calculus (Pantheon) and of The Body Shop, a novel forthcoming from St. Martin's). His article, "The Soul of Man Under Physics," appeared in our January issue.]
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CHARLES DARWIN presented On the Origin of Species to a disbelieving world in 1859 - three years after Clerk Maxwell had published "On Faraday's Lines of Force," the first of his papers on the electromagnetic field. Maxwell's theory has by a process of absorption become part of quantum field theory, and so a part of the great canonical structure created by mathematical physics.
By contrast, the final triumph of Darwinian theory, although vividly imagined by biologists, remains, along with world peace and Esperanto, on the eschatological horizon of contemporary thought.
"It is just a matter of time," one biologist wrote recently, reposing his faith in a receding hereafter, "before this fruitful concept comes to be accepted by the public as wholeheartedly as it has accepted the spherical earth and the sun-centered solar system." Time, however, is what evolutionary biologists have long had, and if general acceptance has not come by now, it is hard to know when it ever will.
IN ITS most familiar, textbook form, Darwin's theory subordinates itself to a haunting and fantastic image, one in which life on earth is represented as a tree. So graphic has this image become that some biologists have persuaded themselves they can see the flowering tree standing on a dusty plain, the mammalian twig obliterating itself by anastomosis into a reptilian branch and so backward to the amphibia and then the fish, the sturdy chordate line - our line, cosa nostra - moving by slithering stages into the still more primitive trunk of life and so downward to the single irresistible cell that from within its folded chromosomes foretold the living future.
This is nonsense, of course. That densely reticulated tree, with its lavish foliage, is an intellectual construct, one expressing the hypothesis of descent with modification.
Evolution is a process, one stretching over four billion years. It has not been observed. The past has gone to where the past inevitably goes. The future has not arrived. The present reveals only the detritus of time and chance: the fossil record, and the comparative anatomy, physiology, and biochemistry of different organisms and creatures. Like every other scientific theory, the theory of evolution lies at the end of an inferential trail.
The facts in favor of evolution are often held to be incontrovertible; prominent biologists shake their heads at the obduracy of those who would dispute them. Those facts, however, have been rather less forthcoming than evolutionary biologists might have hoped. If life progressed by an accumulation of small changes, as they say it has, the fossil record should reflect its flow, the dead stacked up in barely separated strata. But for well over 150 years, the dead have been remarkably diffident about confirming Darwin's theory. Their bones lie suspended in the sands of time-theromorphs and therapsids and things that must have gibbered and then squeaked; but there are gaps in the graveyard, places where there should be intermediate forms but where there is nothing whatsoever instead.(1)
[(1) A.S. Romer's Vertebrate Paleontology (University of Chicago Press, third edition, 1966) may be consulted with profit.]
Before the Cambrian era, a brief 600 million years ago, very little is inscribed in the fossil record; but then, signaled by what I imagine as a spectral puff of smoke and a deafening ta-da!, an astonishing number of novel biological structures come into creation, and they come into creation at once.
Thereafter, the major transitional sequences are incomplete. Important inferences begin auspiciously, but then trail off, the ancestral connection between Eusthenopteron and Ichthyostega, for example - the great hinge between the fish and the amphibia - turning on the interpretation of small grooves within Eusthenopteron's intercalary bones. Most species enter the evolutionary order fully formed and then depart unchanged. Where there should be evolution, there is stasis instead - the term is used by the paleontologists Stephen Jay Gould and Niles Eldredge in developing their theory of "punctuated equilibria" - with the fire alarms of change going off suddenly during a long night in which nothing happens.
The fundamental core of Darwinian doctrine, the philosopher Daniel Dennett has buoyantly affirmed, "is no longer in dispute among scientists." Such is the party line, useful on those occasions when biologists must present a single face to their public. But it was to the dead that Darwin pointed for confirmation of his theory; the fact that paleontology does not entirely support his doctrine has been a secret of long standing among paleontologists. "The known fossil record," Steven Stanley observes, "fails to document a single example of phyletic evolution accomplishing a major morphologic transition and hence offers no evidence that the gradualistic model can be valid."
Small wonder, then, that when the spotlight of publicity is dimmed, evolutionary biologists evince a feral streak, Stephen Jay Gould, Niles Eldredge, Richard Dawkins, and John Maynard Smith abusing one another roundly like wrestlers grappling in the dark.
Pause for the Logician
SWIMMING IN the soundless sea, the shark has survived for millions of years, sleek as a knife blade and twice as dull. The shark is an organism wonderfully adapted to its environment. Pause. And then the bright brittle voice of logical folly intrudes: after all, it has survived for millions of years.
This exchange should be deeply embarrassing to evolutionary biologists. And yet, time and again, biologists do explain the survival of an organism by reference to its fitness and the fitness of an organism by reference to its survival, the friction between concepts kindling nothing more illuminating than the observation that some creatures have been around for a very long time. "Those individuals that have the most offspring," writes Ernst Mayr, the distinguished zoologist, "are by definition . . . the fittest ones." And in Evolution and the Myth of Creationism, Tim Berra states that "[f]itness in the Darwinian sense means reproductive fitness-leaving at least enough offspring to spread or sustain the species in nature."
This is not a parody of evolutionary thinking; it is evolutionary thinking. Que sera, sera.
Evolutionary thought is suffused in general with an unwholesome glow. "The belief that an organ so perfect as the eye," Darwin wrote, "could have been formed by natural selection is enough to stagger anyone." It is. The problem is obvious. "What good," Stephen Jay Gould asked dramatically, "is 5 percent of an eye?" He termed this question "excellent."
The question, retorted the Oxford professor Richard Dawkins, the most prominent representative of ultra-Darwinians, "is not excellent at all":
"Vision that is 5 percent as good as yours or mine is very much worth having in comparison with no vision at all. And 6 percent is better than 5, 7 percent better than 6, and so on up the gradual, continuous series."
But Dawkins, replied Phillip Johnson in turn, had carelessly assumed that 5 percent of an eye would see 5 percent as well as an eye, and that is an assumption for which there is little evidence. (A professor of law at the University of California at Berkeley, Johnson has a gift for appealing to the evidence when his opponents invoke theory, and vice versa.)
Having been conducted for more than a century, exchanges of this sort may continue for centuries more; but the debate is an exercise in irrelevance. What is at work in sight is a visual system, one that involves not only the anatomical structures of the eye and forebrain, but the remarkably detailed and poorly understood algorithms required to make these structures work.
"When we examine the visual mechanism closely," Karen K. de Valois remarked recently in Science, "although we understand much about its component parts, we fail to fathom the ways in which they fit together to produce the whole of our complex visual perception."
These facts suggest a chastening reformulation of Gould's "excellent" question, one adapted to reality: could a system we do not completely understand be constructed by means of a process we cannot completely specify?
The intellectually responsible answer to this question is that we do not know -- we have no way of knowing. But that is not the answer evolutionary theorists accept. According to Daniel Dennett (in Darwin's Dangerous Idea), Dawkins is "almost certainly right" to uphold the incremental view, because "Darwinism is basically on the right track." In this, he echoes the philosopher Kim Sterenly, who is also persuaded that "something like Dawkins's stories have got to be right" (emphasis added). After all, she asserts, "natural selection is the only possible explanation of complex adaptation."
Dawkins himself has maintained that those who do not believe a complex biological structure may be constructed in small steps are expressing merely their own sense of "personal incredulity." But in countering their animadversions he appeals to his own ability to believe almost anything. Commenting on the (very plausible) claim that spiders could not have acquired their web-spinning behavior by a Darwinian mechanism, Dawkins writes: "It is not impossible at all. That is what I firmly believe and I have some experience of spiders and their webs." It is painful to see this advanced as an argument.
rae.org
That is a part of Berlinski's Commentary essay on evolution. I will be posting the rest here in the future including the followup letters and his replies to the article. |
