Evolution and aging
- From: "Lance" <LanceGary@xxxxxxxxxxxxx>
- Date: 10 Feb 2006 00:32:49 -0800
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.
Reviewer Information
Kimberly Hughes is an associate professor of animal biology at the
University of Illinois at Urbana-Champaign. Her laboratory is actively
involved in evaluating evolutionary theories of sexual selection, mate
choice and aging in a variety of organisms, including fruit flies,
honeybees and guppies.
© Sigma Xi, The Scientific Research Society
.
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