MEN and women are so different they might as well be from separate planets, so says the theory of the sexes famously explicated in John Gray’s 1992 best seller, “Men Are From Mars, Women Are From Venus.”

Indeed, sex differences are a perennially popular topic in behavioral science; since 2000, scientific journals have published more than 30,000 articles on them.

That men and women differ in certain respects is unassailable. Unfortunately, the continuing belief in “categorical differences” — men are aggressive, women are caring — reinforces traditional stereotypes by treating certain behaviors as immutable. And, it turns out, this belief is based on a scientifically indefensible model of human behavior.

As the psychologist Cordelia Fine explains in her book “Delusions of Gender,” the influence of one kind of categorical thinking, neurosexism — justifying differential treatment by citing differences in neural anatomy or function — spills over to educational and employment disparities, family relations and arguments about same-sex institutions.