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| Plasticity, Modularity, and Cross-sexual Transfer: A Nonbinary Framework for Sexual Diversity |
| Karen M Warkentin1, 2. 1Boston University, Boston, MA, United States; 2Smithsonian Tropical Research Institute, Gamboa, Colon, Panama |
Same-sex sexual behavior is widespread in animals, yet we lack a general framework that includes same- and different-sex sexual behavior across contexts. I suggest a developmental plasticity framework for sexual diversity, treating sexes as alternative morphs within species and sexual behavior as one of many sex-associated traits that can vary independently. Modular, asynchronous development of sex-associated traits creates opportunities for cross-sexual transfer of trait expression, and mosaic variation suggests such phenotypic recombination is common. Considering the origin of animal sexes and costs of discriminating sex and fertility, I posit ancestral mixtures of reproductive and non-reproductive sexual behavior. Selection on such mixtures enabled the evolution of non-conceptive functions of sexual behavior, in reproductive and non-reproductive contexts. Positive feedback between diversified functions and expression contexts is likely, and both appear prevalent in highly social species, including primates. Greater variation in human sexual behavior evolved with reproductive dependence on alloparental care, in the highly contextual selective environment of cooperative breeding. |