by Lee M. Silver
The Sunday New York Times Book Review
July 8, 2001
Evolution is the most contentious idea in 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 of many stripes 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" that he elucidated. Darwin 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.
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 and 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 out-compete those with the original new gene version. This never-ending
process of one-upmanship is ongoing simultaneously at 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 never-ending
stream of books on the subject. 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 that men and women behave, and the consequences of that behavior for human society
and the economy. Jonathan Weiner's
"The Beak of the Finch" won a Pulitzer Prize for its portrayal of a modern-day
Darwin-like husband-and-wife team who found real-time evolution occurring in the
same archipelago that made Charles Darwin famous.
Ridley's "The Cooperative Gene" is the latest in the stream. While
other authors shower their attention on the macro-world of individuals and societies,
Ridley focuses on the bizarre battles that occur within the micro-world of the
cell and its chromosomes.
To understand the source
of turmoil in this micro-world, 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, literally.
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' brilliant,
and now-classic, 1976 book, "The Selfish Gene." People often
assume that individual animals, like ourselves, are the centerpiece of
evolution, but the longest-lived individuals survive for a miniscule
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 1960'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 are competing with each
other. It is the "selfish gene," not individual organisms,
that can survive for millions of years.
gene's eye view of the world is very different from that of the organism
simply because a successful gene can place itself into a whole group
of genetic relatives. In the gene's eye view, it makes perfect sense
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 (that happen to reside
inside bee bodies).
As Ridley explains,
sex also begins to make 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
eye perspective, however, sex provides an opportunity to get
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 avoid
harmful new mutations but carry a unique genetic combination
that happens to be well-suited for outrunning viruses and other
germs. Sex sacrifices all the losing siblings.
selfish gene theory has been misconstrued by some as a genetic
license to act in purely selfish ways. In fact, it is the
gene's eye view of the world that provides the best evolutionary
explanation for the instinctive expression of altruism, morality,
societal cooperation, and even love. But there's a delicate
balance between cooperation and conflict at all levels of
life from societies to cells.
the micro-world 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. However, as Ridley explains,
genes can become ruthless at the micro-level 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 organismal development
until the production of sperm cells. Like other genes,
this gang is only placed into half the sperm. But as
soon as the 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.
tells other tales of attempted gene mutinies. The
most fascinating is one that has come 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 ongoing
war between the sexes.
ends with speculation on the future evolution
of intelligent life, including a bizarre comparison
of earthly sex to sex among angels (with details
presented in tables on p. 267).
title of Ridley's book suggests that it will
be an antidote to "The Selfish Gene" of
Richard Dawkins. But, in fact, the ideas
presented in "The Cooperative Gene" are
not that different from those of Dawkins,
and they've been expressed in more lively
prose by Dawkins and other authors. Like
the Exodus from Egypt, the story of evolution
must be told anew to each generation. In
both cases, however, it is probably best
to rely on earlier texts.
M. Silver is a professor of molecular
biology and public affairs at
Princeton University and the
author of "Remaking Eden:
How Cloning and Genetic Engineering
will Transform the American Family."