Exploring the evolutionary consequences of same-sex sex: Lessons from the animal kingdom

Scientists have documented thousands of examples of same-sex sexual behavior in non-human animals and have put forth many intriguing theories to explain why such behaviors are so prevalent. However, not much attention has been devoted to the evolutionary consequences of same-sex interactions. Now, a paper published by Cell Press online June 16th in the journal Trends in Ecology and Evolution, highlights the importance of not just focusing on the origins of same-sex sexual behaviors but identifying the influence of such behaviors as agents of evolutionary change.

“Same-sex sexual behavior has long been viewed as a fascinating puzzle from the evolutionary perspective. The most obvious mystery is why animals would engage in sexual behaviors that do not directly result in reproduction,” says lead author Dr. Nathan W. Bailey from the Department of Biology at the University of California, Riverside. Dr. Bailey, along with co-author Dr. Marlene Zuk, sought to broaden the study of same-sex sexual behavior in animals by examining how these sexual interactions might alter evolutionary dynamics within populations or species.

The authors reviewed many studies examining same-sex sexual behavior in non-human animals and identified several research strategies that could be employed to enhance the understanding of how same-sex sexual behavior might have evolutionary consequences. For example, studies of the Laysan albatross found that nearly a third of albatross couples were female-female pairs. The authors pointed out that these pairs were more successful than unpaired females when it came to rearing chicks. As a result, their pairing might have important evolutionary consequences by changing the social dynamics within the population.

The researchers identified other examples where same-sex sexual behavior was potentially a force that might shape the selection of other traits. “Same-sex sexual behaviors are flexibly deployed in a variety of circumstances, for example, as alternative reproductive tactics, as cooperative breeding strategies, as facilitators of social bonding or as mediators of intrasexual conflict. Once this flexibility is established, it becomes in and of itself a selective force that can drive selection on other aspects of physiology, life history, social behavior and even morphology,” explains Dr. Bailey.

The authors also acknowledge that the issue of same-sex sexual behavior is controversial for some people and that research results from studies of non-human species have been cited in media articles addressing human gay rights issues. “It is crucial that scientific contributions from animal studies shed more light than heat on the topic of same-sex behavior, so it is useful to define promising directions for future work and identify pitfalls to avoid as the field matures,” concludes Dr. Bailey.

Bailey et al.: “Same-sex sexual behavior and evolution.” Researchers include Nathan Bailey and Marlene Zuk, of University of California, Riverside, CA.

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