Is Man a Subtle Accident?

The missing link between man and the apes, whose absence has comforted religious fundamentalists since the days of Darwin, is merely the most glamorous of a whoIe hierarchy of phantom creatures. In the fossil record, missing links are the rule: the story of life is as disjointed as a silent newsreel, in which species succeed one another as abruptly as Balkan prime ministers. The more scientists have searched for the transitional forms between species, the more they have been frustrated. Paleontologist Patricia Kelley has traced a burrowing mollusk--Anadara staminea--over 2 million years of the Miocene Epoch, during which time the position of one muscle gradually shifted by 1.5 millimeters. Abruptly, A. staminea disappears, to be succeeded by the closely related species A. chesapeakKensa--in which the muscle has suddenly shifted by 1.5 millimeters in the opposite direction. What kind of evolution is this, which seems to stand on its head the notion of gradual progress from primitive to more advanced species?

Seventy years after quantum theory revolutionized physics, an oddly analogous change has occurred in the theory of evolution--and it is just beginning to filter down to public understanding. Evidence from fossils now points overwhelmingly away from the classical Darwinism which most Americans learned in high school: that new species evoIve out of existing ones by the gradual accumulation of small changes, each of which helps the organism survive and compete in the environment. Increasingly, scientists now believe that species change little for millions of years and then evolve quickly, in a kind of quantum leap--not necessarily in a direction that represents an obvious improvement in fitness. The theory is still being worked out. Among other points of contention, it is uncertain whether the leap takes place in a few generations or over tens of thousands of years. But at a conference in midOctober at Chicago's Field Museum of Natural History, the majority of 160 of the world's top paleontologists, anatomists, evolutionary geneticists and developmental biologists supported some form of this theory of "punctuated equilibria."

'Apples': While the scientists have been refining the theory of evolution in the past decade, some nonscientists have been spreading a new the gospel of creationism-and the coincidence has confused many laymen, including Presidential candidate Ronald Reagan. At a fundamentalist meeting in Dallas, Reagan urged teaching the Biblical version of creation along with evolution, which he said "is not believed in the scientific community to be as infallible as it once was." Having opposed Darwin for 120 years, fundamentalists tend to seize on any criticism of his theories as vindication. The notion of species that come into being very quickly, and then appear to be relatively stable for long periods, appeals to those who believe the earth was populated according to God's design. But the new theories are intended to explain how evolution came about--not to supplant it as a principle. Says Harvard's Stephen Jay Gould, who along with Niles Eldredge of the American Museum of Natural History proposed the punctuated-equilibria theory in 1972: "Evolution is a fact, like apples falling out of trees."

The new theory, according to paleontologist Steven Stanley of Johns Hopkins, draws a crucial distinction between two kinds of evolution: gradual, small changes within a species ("microevolution") and sudden, gross changes that mark the emergence of a new species ("macroevolution"). The former is a specialized case of Darwin's theory of natural selection. Bugs hide deeper in the bark, and woodpeckers evolve longer beaks to hunt them out. But where Darwin, from observations begun in the Galapagos Islands, concluded that enough small changes would eventually create a new species, the revised theory holds that a new species arises by some different mechanism--perhaps even a gross random mutation in a single generation.

This is the theory of "hopeful monsters," a point of bitter contention among geneticists and biologists. To some geneticists, all monsters are hopeless. Such a major change in structure can only be the result of gross chromosome rearrangements. So many other delicate systems would be set awry as a result that the organism could not survive. Not so, says biologist Pedro Alberch of Harvard. A new species may require no more than a mutation in a single gene--there are thousands of genes on most chromosomes--if the gene controls a crucial developmental pathway. He points to a race of salamanders which have a cluster of six unique characteristics, including webbed feet and fused tarsal bones. The identical mutation has appeared at least six different times in the evolution of salamanders, suggesting that only a single small genetic change is involved.

Embryo: Hopeful monsters may seem to be generated at random, but in fact they appear to be subject to the complex laws of development biology. For example, the cellular changes that will lead on the one hand to the development of teeth and hair, and on the other to scales and feathers, are fixed early in the life of the embryo. Therefore, says George Oster of Berkeley, it is unlikely that a furred animal could evolve into one with feathers.

But the significance of hopeful monsters, if they exist, is that they seem to flout the law of natural selection, They are subject to it in a general sense: better monst will, over the long run, drive out weaker ones. But the mutation need not represent an advance in fitness; a mutant gene can spread throughout the population even if it carries no particular survival value, as long as it is not markedly harmful. The web-footed salamanders have no obvious advantage over their digited relatives, but they evolved right along anyway. Among hyenas, a mutation has given rise to a species in which the female develops a useless set of male sexual organs. The iron law of Darwinism--that each new species represents an advance in fitness over its predecessor--seems to have been breached.

Some scientists are still fighting a rearguard action on behalf of Darwinism. A few paleontologists maintain that fossils actually do show gradual evolution over time. Even if fossils don't change, argues Tom Schopf of the University of Chicago, the organisms might have been evolving. Only the hard parts of animals are preserved in the fossil record; species may have undergone considerable evolution in their soft parts and biochemistry without altering their skeletons. Evidence along this line comes from paleobotanist Karl Niklas of Cornell, who has found perfectly preserved leaves from the Miocene Epoch which look exactly like the leaves of modern chestnuts, oaks and maples--but are quite different in their biochemistry.

The paleontologists who have been in the forefront of the new theory don't necessarily believe in hopeful monsters. When they say that new species evolved rapidly, they are speaking in geologic terms. A single generation or 50,000 years is all the same to them. Either would be too short an interval for the intermediate organisms to appear in the fossil record. To the geneticists, this highhandedness about thousands of years has been puzzling, and at the Chicago conference the two disciplines found little common ground. Darwin's great advantage, it now seems clear, was that he lived before the age ofspecialization, when great syntheses of ideas were still possible.

It is no wonder that scientists part reluctantly with Darwin. His theory of natural selection was beautiful in its simplicity, and it has served well for over a century. To tamper with it is to raise a host of questions for which there are no answers. The new theory also raises the troubling question of whether man himself is less a product of 3 billion years of competition than a quantum leap into the dark--just another hopeful monster whose star was more benevolent than most.

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