Dr. Alexandra Kralick offers a queer feminist theoretically-engaged and innovative scientific inquiry into the biology of sex-related variation in the primate skeleton. In this talk, she delves into the biology of the orangutan, a primate known for exhibiting the most pronounced sex differences, or sex dimorphism, in body size among all great apes. Despite this reputation, orangutan males exhibit pronounced within-sex variation. Dr. Kralick traces the phenomenon of plasticity in male orangutans, shedding light on an intriguing group of males often described to be "sneaking" as "female-sized" and sometimes labeled as "sexual predators." Her research measuring orangutan skeletons in museum collections produced findings that shift and challenge the way that features conventionally considered dichotomous according to biological sex are described and examined. Her research not only enriches our knowledge of our non-human primate relatives but also prompts critical reflections on gendered expectations and binary frameworks, both within the non-human primate world and within ourselves.