More is not Necessarily Better: Making Babies in the Modern World - Offspring: Human Fertility Behavior in Biodemographic Perspective - Book Review

Journal of Sex Research, Feb, 2004 by Bradley M. Cooke

Offspring: Human Fertility Behavior in Biodemographic Perspective. Edited by Kenneth W. Wachter and Rudolpho A. Bulatao. Washington, DC: The National Academies Press, 2003, 379 pages. Softcover, $59.00.

Consilience, the conceptual unity of all knowledge (Wilson, 1998), is an idea that most scientists generally ignore because of its impracticality. Yes, it is theoretically possible to understand political science from the perspective of proteomics, for example, but no one currently has either the money or the time to attempt such a project. Yet we live in an era when occasionally one encounters a book whose authors, in the aggregate, come close to providing a coherent multidisciplinary explanation for a phenomenon. Offspring is such a book, and its topic is the myriad factors that influence human decisions to have children.

The emerging problem of declining fertility in Western European and some developing countries motivated the Panel on Population to convene a meeting and to produce this book. This is a problem because, in many cases, fertility rates are at subreplacement levels, leading to real declines in population. However, decreasing fertility in developing countries may be a sign that the quality of life is improving for people, particularly women. As indicated in several chapters, educational achievement is negatively correlated with fertility. As women become more educated, they have fewer children. But beyond the implications of declining fertility for public policy, fertility poses a fascinating puzzle for those of us intrigued by the concepts of evolutionary psychology. If our brains and bodies are merely vehicles with which genes reproduce themselves, why are increasing numbers of humans behaving in such an apparently maladaptive manner?

The contents of the book draw upon several disciplines, ranging from molecular biology to socioeconomic modeling. Together, they achieve the impressive feat of conveying a lot of information about the many facets of reproductive behavior while keeping the reader interested in finding an answer to the paradox. It is beyond the scope of this review to discuss each chapter individually, but I found them all to be of good quality and appropriate for inclusion within the book. While Offspring is not a textbook designed for pedagogy, several chapters provide the non-expert with excellent introductions to the field under review, such as behavioral genetics and behavioral neuroendocrinology.

For example, Judy Cameron's chapter should be read by those who need a succinct introduction to hormones and behavior. She gives a lucid review of the latest issues in developmental and behavioral neuroendocrinology, including discoveries about the sexual differentiation of the hypothalamic-pituitary-gonadal axis and an update on the interactions between stress and reproductive function. Ultimately, of course, the demographic patterns of human fertility behavior at the heart of this book are mediated by societies of individuals, each possessing a brain). Scientists who study phenomena at the group and population levels will appreciate Cameron's description of the proximal mechanisms by which all mammals realize their evolutionary mandate.

Larry Young provides a readable and fascinating description of his research into two closely related species of vole that seem to differ only in terms of their habitat and mating pattern. The male of one species is a reclusive "cad," hanging around only long enough to ejaculate, whereas the other is a perfect "dad"--utterly monogamous and a doting parent. Young and colleagues have found that the two vole species differ in the expression level of a certain receptor in the reward and reinforcement part of the brain. When the expression of the receptor was artificially increased using a gene therapy technique, affiliation toward pups and other conspecifics also increased. Young points to two other pairs of closely related species that likewise differ in their affiliative behavior. Each one of the pairs has been found to differ in the same neurochemical way as the voles.

Tempted as I was to believe that interindividual and cultural differences in "caddishness" and "daddishness" simply reflect a genetic difference as straightforward as that seen in voles, the chapters on behavioral genetics disabused me of that notion. The power of behavioral genetics is that it allows researchers to dissect the relative roles of nature and nurture for a given trait. Two chapters, one by Michael Rutter and the other by Hans Peter Kohler and Joseph Rodgers, provide clear evidence for a strong genetic component of human fertility. However, they also discuss important confounding factors that must be taken into account when interpreting such findings, such as the effect of the genome on the choices one makes about the environment one chooses to live in, and conversely, the effect of the environment on gene expression in the brain.

Perhaps the most striking finding to come from the behavioral genetics chapters is concerned with the interaction of increased educational opportunity with heredity in the expression of fertility behavior. As noted above, educational achievement of women is negatively correlated with fertility. Yet as educational opportunities increase within a society, so too does the heritability of fertility! That is, genes play a greater role in determining the number of children a woman may have in a society such as the U.S., where primary and secondary education are within reach of virtually every citizen, than in an impoverished or repressive society, where factors beyond the individual's control largely prevent her self-actualization.