Around 500 different species of fish are able to change their gender naturally. This is in part due to the fact that unlike mammals and birds, the sex of a fish is not determined by chromosomes. Further, according to the research, fish have been around a lot longer than humans by some 300 million years. They’ve had the time and space (no over fishing or bottom trawling of the oceans back then) to evolve in ways human and other mammals have not yet been able to do. Also, there are more than 26,000 species of fish and a mere 6000 species of mammals. That means more variety in the fish world. Throughout their evolutionary development, fish have adapted to a multiplicity of environments more easily than mammals, and this has created a high degree of diversity, equality and inclusion in the fish cosmos[i].

There are a wide ranging scientific understandings of why some species of fish change their biologically determined gender, and many unknown reasons. For example, size matters when it comes to reproducing offspring. In both male first and female first fish, it is to one’s advantage to be of the opposite sex when one reaches a specific size; like the male kobudia, who was once a female for the first half of its life and was able to reproduce many times. When it reaches a bigger size, it becomes male, and is able to hold sway over a concubine of smaller female fish[ii]. Similarly, Clownfish are very communal, and generally live in confined small group spaces, with a dominant female and male, looking after a school of smaller fish. When the dominant female dies, the male transitions into a female[iii].

This innate and natural way for fish to be able to change their gender improves their ability to pass on their genes. However, not all of the factors which cause fish to change their gender are due to evolved natural ones. Human intervention in their environment through pollution also triggers a fish’s genetic systems into gender alteration. It has been reported that in a Canadian lake, over a 7 year period, constant levels of a synthetic estrogen caused the male fish to become intersexed, and the population complexly collapsed[iv].

In an unprecedented Executive order titled “Defending Women from Gender Ideology Extremism and Restoring Biological Truth to the Federal Government”, Donald Trump and the administration which he runs, will now only recognize women as biologically female, and men as biologically male. They qualify this as “female means a person belonging, at conception, to the sex that produces the large reproductive cell, and mean means a person belonging, at conception, to the sex that produces the small reproductive cell”[v]  In the United Kingdom, the Supreme court decided that the words ‘woman’ and ‘sex’ refer to a biological woman and biological sex”.

Both decisions are representative of using biology as ideology, not biology as science; because, science, in particular biology, would show us that the issue of biological sex and gender in humans is as fluid as the fishes, but not yet as highly evolved. Sex and gender are not straight forward. They are complex, and often not fully understood.

Is there anything we human beings might learn from fish, in our disputes around gender, gender dysphoria, and the role of transgender people in our cultures and societies? Unlike fish our chromosomes, generally speaking, determine our sex. However; it is not as simple as it sounds. While fertilization between a sperm and an egg will express embryonic sex, there’s around a six week lapse before this biological process begins to transform into either a male or female fetus. In the early weeks of gestation all embryos develop in a similar manner, and have similar genitalia, often creating the misperception of a female embryo. Hormonal development in the fetus guides the development of its eventual sex identity, and, not dissimilar to fish, it is the external environmental conditions which can significantly effect sexual differentiation during fetal development. Environmental factors are crucial in shaping the sexual development of an embryo. Levels of the male hormone testosterone, and the female hormone estrogen can influence the formation of sexual differentiation. It is claimed, for example, that high levels of testosterone in a female fetus may masculinize a female embryo[vi].  

Research based science shows us that there is a wide spectrum between the biological description of what constitutes a male and female person. For example, intersex individuals whose physical characteristics are neither male nor female, but somewhere in between, will not fit into a society’s social, legal or political ruling on what constitutes sex and gender. A mix in chromosomes where XX (female) and XY (male) in the same individual, or a missing or additional sex chromosome will impact the sex and gender of a person[vii]. There is no fixed, determined linear embryonic development of sex differentiation in unborn human beings. To quote Veronica Meade-Kelly” It underscores life’s complexities; wherever a gray area exists between two opposing endpoints, it asks us to consider the diverse realities and experiences that make life both more interesting yet harder to comprehend”[viii] It would seem that our scientifically, and culturally defined binary notions of sex and gender identity, are not binary at all.

So, what’s all the fuss about human beings changing gender? Throughout human history, a variety of cultures have recognized, understood and supported non-binary people. From a young age children who questioned, or exhibited non-conforming cultural traits were not ostracized, sent to therapy or labeled abnormal. They grew up, and eventually held recognized status in their respective societies. Examples include, but are not limited to the Hijra in Hindu societies, the Muxe in Mexican society, and the Two Spirit in some North American Indigenous societies.

In the West ideological arguments abound on the complex issue of gender dysphoria, and more widely on transgender persons per se. There is medical and scientific research which affirms the ordinary people who identify as transgender, suffer widely from psychological distress, social marginalization and in some cases violent discrimination in their respective societies.

The recent ruling from the President of the United States of America, and the UK Supreme Court, on the biological definitions of men and women, denies the fluidity and flexibility in nature around gender and biological sex. The West appears to be falling in line with the moral and ethical strictures of theocracies and authoritarian states, when it laws openly discriminate against transgender and non-binary people. It is a reactionary, right wing ideological position, without a compassionate and intrinsic understanding of the innate nature of how we evolve from an embryo to a fetus, to a new born, and onwards to the process of physical, emotional and psychological growth as adults.

Maybe, there’s something we could learn from fish. While human beings may possess advanced cognitive skills when compared to fish; fish don’t reject their collectively diverse, equal and inclusive oceanic social structures. They mostly trust their instinctual behaviors, perception, and learning from each other. Moreover, fish have excellent memory and problem solving skills. For example; they change their gender to manage their social environment. That requires some social intelligence; perhaps more than some human beings have now.

[i] https://www.bbcearth.com/news/fish-are-the-sex-switching-masters-of-the-animal-kingdom

[ii] ibid

[iii] ibid

[iv] https://pmc.ncbi.nlm.nih.gov/articles/PMC1874224/

[v] https://www.whitehouse.gov/presidential-actions/2025/01/defending-women-from-gender-ideology-extremism-and-restoring-biological-truth-to-the-federal-government/

[vi] https://naturalparentingcenter.com

[vii] https://newsroom.ucla.edu/stories/male-or-female

[viii] https://newsroom.ucla.edu/stories/male-or-female