Animal biologists bring up how others may define “biological sex as either female (XX chromosomes) or male (XY chromosomes)” (Odum 2024) but include how some animals do not have any sex chromosomes. Also, about a third of all animals are hermaphrodites. Things like this are also seen in humans, with 1 in 600 people being sex chromosome aneuploid. For animals, including humans, it seems not so easy as just male or female. Animal biologists point out how gender, on the other hand, is not just biology. It is mostly psychology of the “science of the mental and behavioral patterns of the whole animal” (Henriques 2025). Most biologists consider sex as a mostly binary classification of male or female, “according to the reproductive organs and functions that derive from the chromosomal complement” (Mazure 2021). They mostly rely on the chromosomes determining sex. When it comes to gender, in humans, it is the person’s “self-representation as man or woman” (Mazure 2021), or some as nonbinary or others. These are separate from sexual orientation. In biology, gender is how you see yourself. Between both animal behavior and biology, it is mostly agreed that sex can be determined by sexual chromosomes. However, especially in other animals but also present in humans, there are exceptions where individuals have no sex chromosomes, or may have many. This makes it more nuanced than perhaps originally thought. Gender, in humans particularly, is how people see themselves, how they align their identity in society. Animals, however, are a little more complicated. They cannot tell us how they identify, if they do at all. For animal behavior observers, gender is based on behavior differences between sexes. Males, for instance, may not just be biologically similar on a cellular level, but they display similar behaviors characteristic of their sex, or in this case, gender.
Odum AL, et al. 2024. Zoographics in the journal of the experimental analysis of behavior: increasing inclusion of female animals. J Exp Anal Behav. 122(3):392-407. https://doi.org/10.1002/jeab.4220
Henriques G. 2025. A mindedness take on the concept of gender. Psychology today. https://www.psychologytoday.com/us/blog/theory-of-knowledge/202209/a-mindedness-take-on-the-concept-of-gender
Mazure CM. 2021. What do we mean by sex and gender? Yale school of medicine. https://medicine.yale.edu/news-article/what-do-we-mean-by-sex-and-gender/
