BOOK REVIEW
Why We Age
Kimberly Hughes
The Long Tomorrow: How Advances in Evolutionary Biology Can Help
Us Postpone Aging. Michael R. Rose. xiv + 174 pp. Oxford
University Press, 2005. $26.
In an article published in 1990 in Biological Reviews
(65:375-398), Zhores Medvedev of the National Institute of Medical
Research in London reviewed more than 300 biological theories that
have attempted to account for senescence—the progressive and
general deterioration that accompanies aging in humans and most
other multicellular organisms. Most of these ideas are based on
specific molecular or physiological mechanisms, such as oxidative
damage or telomere shortening, and are therefore proximate theories
of aging. In a sense, these postulates address the question
"How do organisms age?"—not "Why do they
age?" The premise of Michael R. Rose's new book, The Long
Tomorrow, is that the ultimate cause of senescence is natural
selection and that evolutionary biology holds the key that will
unlock the secret of longer, healthier lives for humans.
The evolutionary theory of senescence is based on the idea that
natural selection is very effective at eliminating gene variants
(alleles) that have deleterious effects early in life but becomes
progressively less effective in older individuals. To consider an
extreme example, an allele that kills the organism before it has a
chance to reproduce will not be passed on to future
generations—selection has eliminated that allele from the
population. However, an allele that kills an individual only after
the organism has successfully reproduced can be passed on to future
generations, and it can even increase in frequency if it has some
beneficial effect such as increasing fertility. So natural selection
can actively lead to senescence, by favoring alleles that have
beneficial early effects but deleterious late effects. Or senescence
can evolve simply because of the weakness or absence of selection in
old individuals. This dependence of the force of selection on age
can be demonstrated mathematically, using formal population genetic
theory, but it is not particularly intuitive, which has led to a
good deal of misunderstanding in the biology-of-aging literature.
Rose, an evolutionary biologist at the University of California,
Irvine, therefore takes on a difficult task by aiming his text at
those with little or no formal scientific training. It is impressive
that, with few exceptions, the book is appropriate for that
audience: It is consistently simple, the style is informal, and Rose
uses few technical terms and many metaphors and similes. For
example, he explains that after acting powerfully in young people to
keep genes with devastating early effects rare, "at the other
end of life, natural selection snoozes off," having become
"an underachiever, like Woody Allen's God in the film Love
and Death." These metaphors usually work, and a lay
reader will come away with a better understanding both of aging and
of evolutionary biology.
The book can also be profitably read by scientists, even though they
are not the target audience. However, it may make uncomfortable
reading for many researchers, conditioned as we are to prose that is
stripped of any personal dimension. Books written to popularize
science typically restrict subjective comments to the offering of
social or political opinions and don't usually delve into the
author's private life. But Rose's story is intensely personal,
despite his claim in the preface that it is not a memoir. Even
portions of the text devoted to science describe Rose's own research
and that of his close colleagues; the work of others is mentioned
only to provide context. In other words, Rose does not attempt a
balanced or complete treatment of aging science or of the
evolutionary biology of aging. However, if one is prepared to accept
the book on its own terms, it is both engaging and illuminating.
Readers versed in evolutionary biology will particularly appreciate
the fascinating, often hilarious, descriptions of some of the
field's luminaries. The chapter in which Rose describes meeting his
intellectual hero, John Maynard Smith, is entertaining, but not
purely humorous: It ends in disappointment for the young graduate
student, foreshadowing future setbacks and personal tragedies. The
description of Rose's Ph.D. adviser, Brian Charlesworth, is spot on,
capturing both his intimidating intellect and his zany sense of
humor. Descriptions of other scientists are not always as flattering
and are sometimes tinged with bitterness. Nonetheless, Rose's
concise history of prominent theories of aging will keep both
professional and lay readers absorbed and often amused.
The book offers a good introduction to evolutionary thinking and to
the evolutionary theory of aging. Rose presents this theory as a
triumph of evolutionary biology over its more prestigious
cousins—molecular and cellular biology. For those familiar
with his previous book, Evolutionary Biology of Aging
(Oxford University Press, 1991), this perspective will come as no
surprise. But scientists getting their first exposure to this take
on evolution and aging science will probably be startled by Rose's
view of the disciplines that dominated late 20th-century biology.
Cell and molecular biologists who lack a thick skin may come away
insulted by Rose's numerous gibes. His attitude undoubtedly reflects
the difficulties he faced early in his career in getting his
paradigm-shifting views of aging accepted by established researchers.
But Rose and his colleagues have succeeded in bringing about this
paradigm shift by weight of evidence and prolific publication of
articles, mostly in top-tier peer-reviewed journals. Most scientists
studying senescence now accept the rather remarkable idea that
natural selection accounts for such a seemingly maladaptive trait,
although there is still debate over the specifics of some
mathematical models and the interpretation of some data. Rose was
not alone in his efforts to move evolutionary biology to the
forefront of aging research, but as outlined in this book, he was
the first to publish compelling data. He has also continued to
publish convincing and important experimental verification of the
evolutionary models of senescence over the years, and his 1991
book—along with Caleb E. Finch's Longevity, Senescence,
and the Genome (University of Chicago Press, 1990), which
prominently features the evolutionary arguments of Rose and
Charlesworth—was instrumental in making the evolutionary
theory of aging "mainstream."
One of the best and worst things about The Long Tomorrow is
that the book itself is not long; on the contrary, with only 138
pages of text, it is very succinct. The entire book can be assigned
to undergraduates, who should be able to read it quickly and have no
trouble understanding the material. The main drawback is that
serious undergraduates will want more scientific heft. Even
thoughtful lay readers may be occasionally frustrated by the lack of
detail on theories and experiments.
Although some of the metaphors Rose uses in place of the formal
mathematics of population genetics work fairly well, I think many
readers will still be confused about the underlying logic of these
ideas. I know from personal experience that it is quite difficult to
explain these theories without recourse to equations and graphs.
More extended explanation (and even a graph or two) could have been
used to advantage. Rose does provide a glossary and a very useful
resource for the serious reader—an annotated bibliography that
cites many key research papers and technical books.
One of the best chapters is "Birds and Bees," in which
Rose outlines the evolutionary theory that explains why birds live
longer than mammals about the same size, why flying mammals live
longer than nonflying ones, and why tortoises, trees and social
insect queens are long-lived compared with their close relatives.
These captivating examples provide the most convincing
nonexperimental support for the evolutionary view. Another excellent
chapter, "Deadly Serendipity," conveys well the excitement
of science by describing how an experimental oversight led to a new
and important research endeavor for the members of Rose's lab:
determining the relationship between longevity and stress
resistance. Science's challenges are also communicated, as when Rose
describes the poor reception his ideas received at a scientific
meeting he attended soon after moving to the United States from Canada.
After I was asked to write this review, I assigned the book as
reading for two different groups: the undergraduates who work in my
research lab, and a group of faculty, postdoctoral researchers and
graduate students in my department who have an interest in aging. In
both groups, the readers who were least familiar with evolutionary
biology had the most enthusiasm for the book. Thus Rose is
successful both in capturing the imagination of young people with
little exposure to formal science and in convincing advanced
researchers in other fields that understanding evolutionary biology
is important to their science and to their careers. This is a
significant accomplishment.
Now is an especially propitious time to get the word out, because
evolutionary science is under renewed attack from biblical
creationists and advocates of intelligent design. According to a CBS
News poll taken in October 2005, only 15 percent of Americans accept
that humans evolved without God guiding the process. If more of us
follow Rose's lead and explain our research skillfully to the
uninitiated, we may be able to increase that number.