Articles

Same-sex sexual behavior has been extensively documented in non-human animals. Here we review the contexts in which it has been studied, focusing on case studies that have tested both adaptive and non-adaptive explanations for the persistence of same-sex sexual behavior. Researchers have begun to make headway unraveling possible evolutionary origins of these behaviors and reasons for their maintenance in populations, and we advocate expanding these approaches to examine their role as agents of evolutionary change.

Treatment of gender-identity disorders is guided by standards set forth by the World Professional Association for Transgender Health (WPATH). Although not absolute, WPATH's eligibility criteria for hormone therapy and/or genital-reconstructive surgery include participation in psychotherapy. In addition, applicants for genital-reconstructive surgery are required to live at least one year full-time in the preferred gender role, a period referred to as the real-life experience (RLE).

All organisms respond to environmental cues that allow them to organize the timing and duration of life history stages that make up their life cycles. Superimposed on this predictable life cycle are unpredictable events that have the potential to be stressful. Environmental and social stresses have deleterious effects on life history stages such as migration, reproductive function and molt in vertebrates. Global climate change, human disturbance and endocrine disruption from pollutants are increasingly likely to pose additional stresses that could have a major impact on organisms.