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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 whole 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. chesapeakensa-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 evolve 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
mid-October 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
anew 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 monsters 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 of specialization, when great
syntheses in 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.

  JERRY ADLER with JOHN CAREY in Chicago