Please explain - abnormally low? It's unclear what you are referring to.
"They do that because they were born that way."
If you say that about homosexuals, you are tolerant and realistic. If you say it about blacks, you are racist (unless you're black yourself). If you say it about women, you may or may not be sexist, depending on who is manning (er, womanning) the feminist battle stations. If you say it about men, you just might be a writer for Esquire. But if you say it about conservatives, you're a scientist.
Over the past decade, a new fad has taken hold among academics and liberal journalists: call it the new science...
Again I ask, what are the time periods being compared in the current literature. I have, in the course of reading the most abundant literature seen as low a 100 years and maybe as long as few 100 thousand, rare do you see millions.