Darwin's Legacy: An Evolutionary View of Women's Reproductive and Sexual Functioning

Abstract

On the Origin of Species, published just over 150 years ago, has deeply influenced thinking in both scientific and wider communities. Darwin's legacy includes recognition of the fact that all organisms evolve; that variation within and between species is natural and normal; and that an evolutionary approach to understanding the sources and consequences of this variation comprises theoretical frameworks, testable hypotheses, and rigorously collected evidence. With an eye toward facilitating communication and productive collaboration among researchers from different intellectual traditions who nonetheless share a common interest in women's reproductive and sexual functioning, we discuss evolutionary concepts and models, summarize the known variability in ovarian functioning and consider the implications of this variability for conducting sex research, and evaluate the relative merits of various biomarkers that serve as proxy measurements of a woman's reproductive and hormonal status. With these perspectives and methods from reproductive ecology at hand, we examine several contentious issues: the links between hormones and sexuality in premenopausal and perimenopausal women, the causes of premenstrual syndrome, and the existence (or not) of menstrual synchrony. In none of these cases is as much known as is often claimed. In each, there are abundant opportunities for innovative, albeit challenging, research.

Acknowledgments

We thank Dr. Jacques van Lankveld, ARSR editor, for the invitation to write this paper and for his extraordinary support and patience during its preparation, and we sincerely appreciate the thoughtful commentary and suggestions from four anonymous reviewers. We also thank Dr. Jonathan Thornburg (Astronomy Department, and IUCSS, Indiana University), who prepared the figures and read innumerable drafts, and Dr. Tobias Deschner (Max Planck Institute for Evolutionary Anthropology) and Caroline Deimel (Anthropology Department, Indiana University) for engaging discussions on nonhuman primate sexuality.

This paper is dedicated to the women who created Codex Thetis Kora (http://thetiskora.com), a multilens expression of women's voices, strength, and sexuality that complements an evolutionary view of women's bodies. Kudos to Suzanne and Gök Sarioglu, Petra Accipiter, Stephanie Cottell, Ann Eriksson, Myla Frankel, Dawn Gordon, Gillian Gwyer, Ann Keir, Maureen Loiselle, Carol Sowerby, Jean Tannahill, Vicki Walker, Simone Weber Luckham, and Janice Young.

Notes

^a C = cycles, W = women.

^b selected sample.

^c excluded “anomalous” segments; ≥6 consecutive segments/woman.

^d natural family planning trials; women selected for regularity.

^e significantly different lengths from other 4 countries.

^f geometric mean; excludes short phases; start defined as day after LH surge; 14.13 + 0.31 time from ovulation = 14.44 days.

^g geometric mean; excluded cycles >40 days; phase end = LH surge-1; add 1 day for LH peak and 0.7 days to ovulation = 14.6 days.

^h selected for regular cycles 21–42 days long; follicular includes days of LH surge and ovulation.

^a Percent of all cycles; different number of cycles/woman.

^b women observed for 3 months.

^c similar rates in 30–39 year olds.

^d Students & staff at midwest/northeast colleges.

^e mean cycles/woman = 6.7.

^f percent of women w/ ≥1 anovulatory cycles >35 days long.

^g restricted to cycles 25–35 days long.

^h winter season.

ⁱ sample selected for high fertility.

^a Modified from Campbell and Rockett (2006).