If you haven’t yet read Alan Shlemon’s article from earlier this year answering the question “What is a woman?” I recommend you do so now. Alan makes the point that both the definition of a woman and the explanation for why there are only two sexes depend on the fact that there are only two types of gametes—sperm and eggs. A man’s body is organized around producing sperm (whether or not he’s fertile), and a woman’s body is organized around producing eggs (whether or not she’s fertile).

In the short video “Chromosomes Are Not Sexes” (below), Zachary Elliott gets into the science behind Alan’s argument above, explaining why chromosome variations other than XY and XX still only produce either a man or a woman, concluding with the main point we need to remember when discussing this topic with critics:

They incorrectly argue that chromosome variation forms additional sexes, and yet, none of these chromosome variations result in a third role in reproduction. They still result in just two: either male or female. In fact, while most chromosome variants beyond XX and XY result in infertility, when individuals with this condition are fertile, they produce either sperm or eggs, not a third gamete type. Thus, they are not additional sexes.

The video is clear, simple, and worth your time. Its short length also makes it an easy way to share this scientific truth with others.

Elliott has many more videos discussing the scientific differences between men and women (“sourced directly from scientific literature,” with citations) available on his website.