Evolution now : a century after Darwin / edited by John Maynard Smith.

Date:
1982
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Evolution now : a century after Darwin / edited by John Maynard Smith. Source: Wellcome Collection.

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    THE EVOLUTION OF BEHAVIOUR 239 than to daughters only in cases where 'reproductive success varies more widely among males than females'. For human gestation, it is known that more resources are devoted to a male fetus than to a female one, resulting in significantly higher birth-weights for male infants^^. Since there is no cultural influence which might affect the developing fetus differentially according to its sex, this may be taken as indicating some biological basis for a mating system in which human males would exhibit more variation in reproductive success than would females; that is, polygyny or promis¬ cuity rather than monogamy. Setting aside the trends in degree of sexual dimoфhism and relative weight of testes, the other patterns in the figure are mainly concerned with the conspicuousness of the genitalia (size of erect penis, whether or not the testes are pendulous and so on). These patterns have not yet been compared systematically among primate species, and the evidence they offer about mating systems can be sub¬ jected to an indecisive variety of interpretations. Note the special importance of the study by Harcourt et al. in these attempts to reconstruct the breeding systems of our human ancestors by broad comparisons among primates. Earlier work tends to rule out monogamy, but makes little distinction between multimale and unimale breeding groups; the current study of the relative size of testes now tends to exclude multimale systems. Monogamy may, of course, nonetheless be the optimal system in certain modem societies. Much work on birds, mammals and other creatures indicates that monogamy often emerges when large investments in the offspring necessitate cooperation between the parents. It is possible that the increasing dependence of the human infant, associated with progressively increasing brain size and cultural complexity, has favoured culturally determined monogamous tendencies in various human societies, even though these have not led to the complete suppression of biological indicators of a polygynous ancestry. In brief, it seems likely that our moфhology is that of a species with unimale breeding groups but that these biological antecedents are today often overlain by extremely powerful socioeconomic determinants. 1. Harvey, P. H., Kavanagh, M. & Glutton-Brock, T. H, /. Zoo/. Land. 186, 475 (1978). 2. Martin, R. D. Nature, News & Views 287, 273 (1980). 3. Short, R. v. Adv. Study Behav. 9,131 (1979). 4. Short, R. V. /. Reprod. Pert. Suppl. 28, 3 (1980). 5. Short, R. V. in Reproductive Biology of the Great Apes (ed, Graham, C. E.) 319 (Academic, New York, 1981). 6. Wrangham, R. W. Soc. Sci. Inf. 18, 335 (1976). 7. Galdikas, B. M. F. in The Great Apes (eds Ham¬ burg, D. A. & McCown, E. R.) 195 (Ben¬ jamin, 1979). 8. Harcourt, A. H., Fossey, D., Stewart, K. ]. & Watts, D. P. /. Reprod. Pert. Suppl. 28, 59 (1980). 9. Martin, R. D. Z. Morph. Anthrop. 71,115 (1980). 10. May, R. M. & Rubenstein, D. I. in Reproductive Biology, Vol. 6, 2nd edn (eds Austin, M. & Short, R. V.) (Cambridge University Press, 1981). 11. Brand, H. M. Lab. Anim. 14, 301 (1980). 12. Van Horn, R. N. Prog, reprod. Biol. 5, 181-221 (1980). 13. Rowell, T. E. in Social Communication among Primates (ed. Altmann, S. A.) 15 (Univer¬ sity of Chicago Press, 1967). 14. Ford, C. S. & Beach, F. A. Patterns of Sexual Behaviour (Eyre & Spottiswood, London, 1952). 15. Glutton-Brock, T. H., Albon, S. D. & Guiness, F. E. Nature 2Й9, 487(1981). 16. Gibson, J. R. & McKeown, T. Br. j. soc. med. 6, 152(1952). Robert D. Martin is Reader in Physical Anthropology at University College, London and Robert M. May is Professor of Biology at Princeton University. This article first appeared in Nature Vol. 293, pp. 8-9; 1981.