On this episode of Unsupervised Learning Razib talks to Nathan Lents about his new book, The Sexual Evolution: A Provocative Look at Sexual Behavior Through the Lens of Evolution. A professor at John Jay College in New York City, Lents earned a Ph.D. in Pharmacological and Physiological Sciences in 2004 at Saint Louis University School of Medicine, and did his postdoctoral fellowship in cancer genomics at NYU Medical Center. Lents’ research ranges from the evolution of molecular mechanisms to behavioral ecology. He is also the author of Not So Different: Finding Human Nature in Animals and Human Errors: A Panorama of Our Glitches, from Pointless Bones to Broken Genes.

Lents reached out to Razib after hearing his podcast with Conn Carroll, about his book Sex and the Citizen: How the Assault on Marriage Is Destroying Democracy. Lents felt that Carroll overemphasized the role of monogamy during humanity’s long forager phase, and more precisely, failed to distinguish social monogamy and genetic monogamy. As noted in The Sexual Evolution, many socially monogamous species, like most birds, engage in enough extra-pair copulation so that genetic fidelity is considerably lower than 100%.

Razib and Lents then go back to first principles, talking about the origins of sex, and its persistence in the face of the two-fold cost of reproduction in dimorphous organisms. They discuss why specialized males and females exist in complex organisms as distinct as flowering plants and humans. Lents also discusses the reviews empirical literature on homosexual behavior, variation in sex differences across many classes of organisms and the application of evolutionary thinking to our understanding of the human past. Then they discuss the relevance of evolutionary biology for understanding the human present, and our current debates about marriage, sex and gender. Finally, they consider the differences between sex and gender, and the idea that both can be conceptualized in a nonbinary fashion.