The Cooperative Gene
Evolution is the most contentious idea from contemporary
biology. Half of all Americans don't believe it has anything to do with our
appearance on earth, and they'd prefer not to have their children corrupted by
its teaching. At the same time, an understanding of evolution has never been
more important to scientists, who use it to gain deeper and richer insights into
all aspects of life, from biological molecules to whole ecosystems and from
human behavior to human disease.
Whether they accept it or not, nearly all American adults
have heard of Darwin and his theory. But most don't grasp the principle of
''natural selection'' he elucidated.
He started with just two basic assumptions. The first is that new heritable
changes pop up at random within individual organisms. The second is that certain
heritable changes provide individuals with a better chance at surviving and
reproducing in competition with their neighbors. Surprisingly, if you accept
these two assumptions as facts -- and they are facts of the entire past history
of life on earth -- you must accept evolution as a logical consequence.
We now understand that heritable changes result from mutations that produce
new versions of genes. If a particular new gene causes
individuals to propagate (on average) more children, then with each generation
greater proportions of the population will carry the new gene until eventually
it is found in all individuals. In the language of evolution, this gene has been
''selected'' by nature. However, sooner or later an even newer gene version will
appear that allows individuals to outcompete those with the original new gene
version. This never-ending process of one-upmanship goes on simultaneously in
thousands of genes in every population of living creatures.
While the basic principles of Darwinian evolution are
simple, the devil -- as well as the delight -- is in the details. And it is the
fascinating details and imagined devils that are the basis for a stream of
books. Some make for beautiful reading. Stephen Jay Gould's earliest popular
books charmed readers with lucid descriptions of the evidence for evolution in
dead fossils and living animals. Matt Ridley (no relation to the author of the
book under review) explored the scandalous impact of evolution on the different
ways men and women behave, and the consequences of that behavior for human
society and the economy. ''The Beak of the Finch,'' by Jonathan Weiner, won a
Pulitzer Prize for its portrayal of a modern Darwin-like husband-and-wife team
who found real-time evolution occurring in the same archipelago that made Darwin famous.
''The Cooperative Gene,'' by Mark Ridley, an Oxford
zoologist, is the latest in the stream. While others shower their attention on
the macroworld of individuals and societies, he focuses on bizarre battles that
occur within the microworld of the cell and its chromosomes.
To understand the source of turmoil in this microworld, it
is first necessary to appreciate a major problem in the Darwinian view of
evolution that Darwin himself recognized. Natural selection should favor only
those individuals who are best able to survive and reproduce themselves. ''Nice
guys'' who squander precious time and energy to help others should finish last,
which means that we shouldn't find them in existence today. So how do we explain
the male praying mantis, who gets one chance to copulate with a female before
she eats him up? And how come ant and bee colonies are filled mostly with
workers who never reproduce at all?
An explanation for these and many other organismal
behaviors that go against the ''survival of the fittest'' dictum came through a
startling new interpretation of natural selection, first popularized in Richard
Dawkins's1976 classic, ''The Selfish Gene.'' People often assume that individual
animals, like ourselves, are the centerpiece of evolution, but the longest-lived
individuals survive for a minuscule speck of time in the grand scheme of life.
The only thing that can survive longer is a clever gene. It was not until the
60's that evolutionary biologists began to recognize the implication of these
facts. They realized that genes were not being used by organisms as much as
organisms were being used by their genes. It is the genes that compete with one
another. It is ''the self gene,'' not individual organisms, that can survive for
millions of years.
The gene's-eye view of the world is very different from
that of the organism simply because a successful gene can place itself in a
whole group of genetic relatives. It makes perfect sense for the gene to
sacrifice some of those relatives when the sacrifice helps to increase the
gene's survival and replication through other relatives. This logic is amenable
to a precise mathematical formulation that explains all sorts of biological
phenomena in which individual organisms express instinctive behaviors that are
antithetical to their own personal survival or reproduction. Praying mantis
genes sacrifice post-copulatory males so that better-nourished females can
produce more copies of praying mantis genes. Bee genes organize large colonies
of sterile workers for the sole purpose of assisting the queen in her production
of large quantities of bee genes.
As Ridley explains, sex also makes sense in light of the
selfish gene. If the organism really mattered, we would expect it to reproduce
by cloning. Instead, almost all complex organisms compromise their reproduction
by putting only half their genes into their offspring, together with someone
else's genes. From the gene's perspective, however, sex provides an opportunity
to be placed into multiple organisms, in the company of different combinations
of other genes. Each time an organism is formed, the genetic equivalent of
thousands of dice are thrown. The odds are that a small number of offspring will
be winners because they carry a unique genetic combination that happens to avoid
harmful new mutations and is well suited for outrunning viruses and other germs.
Sex sacrifices all the losing siblings.
The selfish gene theory has been misconstrued by some as a
genetic license to act in purely selfish ways. In fact, the gene's-eye view of
the world provides the best evolutionary explanation for the instinctive
expression of altruism, morality, social cooperation, even love. But there's a
delicate balance between cooperation and conflict at all levels of life, from
societies to cells.
Within the microworld of the cell, the selfishness of
single genes is normally tempered by their need to cooperate with neighboring
genes in construction of the bodies that reproduce them all. But, as Ridley
says, genes can become ruthless at the microlevel when the opportunity arises.
In some species of mice and flies, there is a deceitful gang of genes that
quietly cooperates with its neighbors throughout development of the organism,
until the production of sperm cells. Like other genes, this gang gets into only
half the sperm. But as soon as division takes place, the gene gang assassinates
the brother sperm in which it doesn't reside. As a result, it manages to avoid
the reproductive compromise of sex as it transmits itself to all offspring of
the males that carry it. It turns out that assassin genes are not very common
because their gene victims eventually figure out how to fight back. In Ridley's
words, ''gene justice'' will always prevail at the end of the day.
Ridley tells other tales of attempted gene mutinies. The
most fascinating is one that came to light over the last decade in the form of
multiple battles between genes given to a fetus by its father and those provided
by its mother. The father's genes direct the fetus to suck up all the mother's
resources at the expense of the mother's future health and fertility. But the
mother's genes have evolved the ability to counteract each of many hijacking
attempts. What we see within our own genomes is a current truce in this war
between the sexes.
Ridley ends with speculation on the future evolution of
intelligent life, including a bizarre comparison of earthly sex to sex among
angels (with numerical details presented in tables).
The title of Ridley's book suggests an alternative
perspective on the gene's role in evolution from that presented by Dawkins in
''The Selfish Gene.'' But Ridley's ideas are not that different, and they've
been expressed in more lively prose by others. Like the exodus of Israel from
Pharaoh's Egypt, the story of evolution must be told anew to each generation. In
both cases it is probably best to rely on earlier texts.
This review of "The Cooperative Gene" by Mark Ridley was written
by Lee M. Silver, a professor of molecular biology
and public affairs at Princeton University, is the author of ''Remaking Eden:
How Cloning and Genetic Engineering Will Transform the American Family.''
It appeared in The New York Times Review of books on Sunday, July 8, 2000.