, Volume 6, Issue 3, pp 197-220

The human breast and the ancestral reproductive cycle

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This paper, using modern Darwinian theory, proposes an explanation for the increasingly high incidence of breast cancer found among pre-and post-menopausal women living today in westernized countries. A number of factors have been said to be responsible: genetic inheritance (BRCA-1), diet (specifically the increased consumption of dietary fat), exposure to carcinogenic agents, lifetime menstrual activity, and reproductive factors. The primary aim of this paper is to demonstrate the value of a perspective based on Darwinian theory. In this paper, Darwinian theory is used to explore the possibility that the increased incidence of breast cancer is due primarily to the failure to complete in a timely manner the reproductive developmental cycle, beginning at menarche and continuing through a series of pregnancies and lactation. On the basis of comparative data, we assume that most women in ancestral populations began having children before age 20 or so and tended to remain either pregnant or nursing for most of their adult lives. If a woman did not have a child by age 25 or so, she probably would never have one. Therefore, selection would probably not have acted against deleterious traits, such as cancer, that appeared after that age, just as it does not act against such traits in old age.

This article is based upon a paper presented at the Sixth Annual Scientific Meeting of the Human Behavior and Evolution Society, June 18th, 1994, University of Michigan, Ann Arbor.
Kathryn Coe is a Ph.D. candidate in anthropology at Arizona State University and project director of an NCI grant focusing on cervical and breast cancer in Hispanic women. Field research for her doctoral dissertation focused on the health, fertility, and culture of the Chachi Indians of the coastal rain forest of Ecuador.
Lyle Steadman is an assistant professor of anthropology at Arizona State University. He has conducted research for more than two years among the isolated Hewa of Papua New Guinea. His research interests include evolutionary theory and culture, particularly religion and kinship.