Fausto-Sterling is not an incidental figure in modern debates about sex. Her famous 1993 essay The Five Sexes helped popularize the idea that the familiar male-female binary is biologically inadequate. She proposed additional “sexes” based on intersex conditions and argued more broadly that sex should be understood as a continuum.

Those arguments became enormously influential. In our view, they also created lasting confusion by encouraging people to mistake variation in sexual development for evidence that biological sex itself is not binary. But when it comes to sexual reproduction, the distinction is straightforward: females are organized around producing ova and males around producing sperm. There is no third gamete type or reproductive role, and intersex conditions do not create one.

One of us has examined these arguments in an essay for Skeptic. Other evolutionary biologists, including Colin Wright, have also offered detailed treatments of the issue.