Fertility is undoubtedly the least often discussed facet of the reproductive process, in large part because scientists haven't had the tools needed to study it until recently, but also because, well, it's just not very sexy. But as Ellison, professor of anthropology and dean of the Graduate School of Arts and Sciences at Harvard, shows in this comprehensive study, fertility plays a far more important role than the sexual act in our development as a species. "It may well be... that it was an adaptation in our reproductive physiology that originally set the stage for our intellectual and cultural development," he asserts. But important aspects of female physiology aren't obvious outcomes of natural selection: the head size required for the relatively large fetal brain played a major role in the high incidence of women's death in childbirth in earlier centuries. The author tells us that scientists have discovered that there seems to be little correlation between sperm counts and male fecundity. One man can have the minimum normal sperm count of 15,000-20,000 per milliliter and another an astonishing 250 million, but both face roughly the same odds of impregnating a fertile egg. Ellison tilts perhaps a little too strongly toward female fertility; males receive only one relatively short chapter. The book is not an easy read and will probably appeal mainly to professionals in medicine and related fields. Still, any reader will be astounded not only by how much has been learned about human fertility but by how much still remains to be explored. (Mar.)
Copyright 2001 Reed Business Information, Inc.
--This text refers to an out of print or unavailable edition of this title.
For many of us, one of the most intellectually exciting areas of biomedical research during the past quarter-century has been reproductive physiology, which has revealed the basic mechanisms of reproduction in all their chemical complexity and with all their exquisite temporal coordination. Given the nature of scientific research, much of this work has been narrowly focused and specialized, leading to a somewhat atomized and decontextualized picture of the reproductive process as a whole. In this stimulating book, Harvard anthropologist Peter Ellison boldly attempts to correct that picture. Reproduction, he argues, must be seen as an integrated system operating in specific environments. And because reproduction is closely linked to genetic fitness, it must ultimately be understood as the outcome of evolution by natural selection. Moreover, since contemporary fertility patterns are heavily dominated by deliberate birth control, the ecology and evolution of human reproduction are best studied in small, isolated rural communities that maintain something of their traditional way of life. In large part, Ellison succeeds admirably in making his case, although some of his conjectures are bound to spark debate and controversy -- not necessarily a bad thing in science.
Not surprisingly, Ellison spends a considerable amount of time describing the results of his own extended fieldwork among Efe hunter-gatherers and Lese horticulturalists living in the rainforests of the Democratic Republic of Congo. This work has been innovative in bringing modern endocrinologic methods into anthropologic field studies. Ellison has also been involved in similar projects in other parts of the world, and the results of those projects receive attention as well. At the same time, he provides a broad overview of a wide range of work in demography, epidemiology, anthropology, and basic reproductive biology. And he weaves all these disparate lines of research together to provide an integrated picture of female reproductive cycles, pregnancy and pregnancy loss, parturition, lactation and lactational infecundability, reproductive maturation, spermatogenesis, the effects of energy balance on reproduction, and reproductive senescence (with special emphasis on the evolution of menopause). As this list suggests, much of the focus is on female physiology. Males get fewer than 30 pages of their own. In part, this focus reflects the author's own research interests, but it can also be justified on evolutionary grounds. As Ellison makes clear, the physiologic burdens of childbearing are vastly greater for women than for men. Consequently, natural selection has had more work to do over the course of human history and prehistory to reconcile female reproductive effort with limited local resources, especially food resources. Male reproduction is cheap by comparison in terms of energy cost.
Ellison argues convincingly that an evolutionary approach to reproduction is essential, but he does not always convey just how hard it is to apply such an approach convincingly. Good laboratory work is relatively easy to do; good fieldwork is much more difficult. And it is vastly more difficult to make a convincing case out of the sorts of cross-population and cross-species comparisons that are the foundations of inference about evolution. As researchers progress from one type of study to the next in this sequence, it becomes more and more difficult to maintain control and replicability. Evolutionary studies, in particular, often involve arguments about plausibility and ex post facto reasoning. It is not that any thinking biologist doubts that the human reproductive process evolved by natural selection; the problem, rather, is one of providing critical tests of particular evolutionary hypotheses.
Ellison is brilliant at concocting plausible ecologic and evolutionary hypotheses (which is no mean feat). And he is usually fairly realistic about the difficulties involved in testing them (his discussion of the evolution of menstruation in hominids is a good example). But occasionally, he treats his own speculations as if they were established science. For example, many physiologists will find his arguments about the mechanisms involved in parturition and lactational anovulation to be controversial (to say the least), and demographers are sure to howl over his assertion that social factors are generally unimportant as immediate causes of variation in human fertility. But even if most researchers will not yet be ready to go as far as Ellison on many of these issues, his forceful arguments are sure to inspire the difficult empirical work that is needed in order to support or refute them.
Ellison's writing is consistently graceful, cogent, and clear. His five-page overview of the basic logic of hormones, receptors, and transport proteins, written for the general reader, is one of the most elegant I have ever read. Occasionally, it might have been useful to supplement his prose with diagrams and figures, but for the most part he shows just how effective English can be as a medium for scientific expression -- something that cannot be said of most science writing.
In sum, Ellison's book is a thought provoker and occasionally an objection provoker. It is brimming with ideas, many of them conjectural but all of them stimulating. It should be read not as a catalogue of established scientific knowledge but as an intellectual road map for future research on reproductive ecology. It deserves to set an agenda, even if many of its details ultimately turn out to be wrong.
James Wood, Ph.D.
Copyright © 2001 Massachusetts Medical Society. All rights reserved. The New England Journal of Medicine is a registered trademark of the MMS.
--This text refers to an out of print or unavailable edition of this title.
