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Mothers and Sons
review by R JOHN IRWIN NZ Listener 7 Nov 98 43
MATERNAL PERSONALITY, EVOLUTION AND THE SEX RATIO, by Valerie J Grant (Routiodge, $56.95).
The extraordinary hypothesis advanced in this book is that the sex of a child is determined partly by the mother's personality. Stated in this bald manner, one could be forgiven for regarding Dr Valerie Grant's attempt to provide a scholarly account of this idea as an example of pathological science, but it is not. Let me describe why. Grant (a lecturer in the psychiatry and behavioural science department at Auckland University) describes six separate studies showing that women who score highly on a carefully constructed personality questionnaire of dominance are more likely to bear sons than those who score lower on this measure. But she goes much further than that. Unlike pursuers of pathological science (the study of extra-sensory perception is a fine example), she seeks mechanisms to account for her finding; and she relates it to a rich web of biological theory and experiment. The central component of the underlying mechanism is thought to be testosterone. This predominantly male hormone is also found in small amounts in women. Women with testosterone tend to be more dominant, and the hormone circulating at the time of conception in the uterine environment regulates the reproductive processes to increase the chances that a Y sperm fertilises the ovum. [Although the ovum does 'decide' the sperm' the Y-chromosome is thightly packed so this particular mechanism may be in question. Other possibilities are differential rates of implantation of male and female offspring - CK].
The maternal dominance hypothesis therefore may be an epiphenomenon an accidental by-product, though perhaps a readily measurable one, of the underlying cause that tips the balance one way or the other to determine a child's sex. Testosterone is the physiological mechanism that links maternal dominance and a tendency to have male offspring. But I doubt that Grant would accept this simplification. After a valuable review of the evidence from developmental psychology and elsewhere, she argues that the mother's personality not only makes her more likely to conceive a child of a particular sex, but also renders her more suitable to raise a child of that sex, a suitability that affords an evolutionary advantage and has an evolutionary origin. There is much more. Consider the puzzling fact that, after a war, more boys are born than usual. Divine providence is one explanation. A more satisfying and testable account is offered by the maternal dominance hypothesis. Tough times are stressful times; additional stress causes a temporary shift in the average level of female testosterone. Result: more boys. I believe that Grant made a tactical mistake by including in an appendix to the book her questionnaire of maternal dominance. Hasty readers of the book will dismiss this simple questionnaire and, along with it, her research. They will not have read the technical literature in which the test's development is presented, and in which the scientific material that underpins it is described. The test's simplicity belies its sophisticated foundations. Early on, Grant describes the history and development of the concept of dominance as a personality trait and circumscribes its meaning. It is not, for example, to be confused with domineering; a dominant personality is authoritative rather than authoritarian. Nor is such a trait to be thought of as necessarily a life-long characteristic. Indeed, she presents evidence that it tends to decline in later years. Nevertheless, she recognizes that personality testing is a "soft" part of psychological science, and she provides a balanced review of the strengths and weakness of the various methods of assessing it, including those of tests like her own. Students of psychology will find this a valuable account. This fair-minded approach is characteristic of the book as a whole, including its account of maternal dominance in animals. Those working in animal husbandry are immensely interested in the possibility of predicting, and especially in the possibility of controlling, the sex of the animals they breed. The research on this topic, as on others, is always described in sufficient detail for the reader to evaluate the author's own assessment of it; it helps the reader gain an appreciation of the degree of certainty, and the aura of doubt, that surrounds any scientific finding. Here, too, she finds examples of good science that directly support her hypothesis: dominant red deer, it turns out, give birth to more male infants than less dominant deer, a finding all the more supportive of her hypothesis because the discovery was made independently of her own work. Some human prospective parents are curious to know, and sometimes anxious to determine, the sex of their offspring. Regrettably, some bad science on this topic found its way into good journals and thence into the popular press. She recounts how only gradually, and partly as a result of research undertaken at National Womens Hospital in Auckland, were these phony claims able to be refuted. This is a brave account of a seemingly implausible idea, written with an easy grace. Like any good scientist, Grant is prepared to take conceptual risks to advance testable and potentially refutable hypotheses. She goes further than seeking out investigations that are in accord with her hypothesis, and shows how it makes sense of otherwise puzzling phenomena, like the change in the sex ratio after war. She reviews a vast body of research, much of it (like reproductive endocrinology) highly intricate, yet she makes it comprehensible to the non-specialist reader. But the real test of the underlying mechanisms that she postulates must await deliberate attempts at the biological level to refute them. The story of her own attempts at the psychological level is presented with modest charm. It's a story that deserves a wide audience.