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November 28th 2017 print

David Archibald

Human Biology’s Mardi Gras Parade

From an evolutionary point of view, what's the point of a variant that makes reproduction less likely? The answer would seem to be that a loss of fitness is acceptable if it brings a greater and offsetting benefit -- a theory recently blessed with greater credence by, of all things, facial-recognition technology

tom of finlandIf adult gays want to wed there will soon be no law blocking their paths to the altar. Some of us tried to warn them not give up their carefree lifestyles, but to no avail. Soon many will learn the full horror of the Family Court, making them entirely equal with heterosexuals in every respect.

But why do we have gays in the first place, homosexuality being something of an evolutionary a conundrum. Theoretically, same-sex attraction should have been bred out of the population long ago, yet it persists. There is plenty of evidence that homosexuals are born that way and, therefore, are part and parcel of the human condition. Homosexual males tend to have a longer index finger than middle finger (as heterosexual females do), with the opposite in lesbians.  Birth order affects the incidence of homosexuality with it increasing with the number of males born to a woman. Even artificial intelligence can detect sexual orientation from photographs with up to 91% accuracy (for more on this, see the New Yorker‘s recent article). It seems the genes that control the incidence of homosexuality are deep within our genetic coding.

So why does humanity include a variant that makes reproduction less likely? The answer appears to be that a loss of fitness is acceptable if it brings a greater and offsetting benefit. As the incidence of homosexuality increases with the number of sons born to a woman, it appears to be the result of a variety of immune responses to the higher testosterone levels associated with male foetuses — which, in turn, suggests the rate of homosexuality is a trade-off between the loss of reproductive fitness and the maleness of the rest of the crop. In effect, the reproductive fitness of 1.4% of males is sacrificed so that the rest can have higher testosterone levels.

A model for this is sickle cell anaemia which developed as a genetically inherited disease in response to malaria. The malaria parasite’s complex lifecycle sees it spend part of it in red blood cells. In sickle cell anaemia, a proportion of the red blood cells are shaped, as the name asserts, like a sickle instead of round. In malaria-infected individuals with sickle cell anaemia, the parasite causes the red blood cells to rupture prematurely with the result that it is unable to reproduce. In West Africa, the incidence of sickle cell anaemia is four percent of the population. In areas where malaria is a problem, an individual’s chance of survival actually increases if he or she carries the sickle-cell trait.

sickle cell maps

Science attempts to explain the universe. The paradox of homosexuality’s loss of fitness is explained by the greater good for normal males. Gays have ‘taken one for the team’ so the rest of us can do a better job of looking after the females.

Thanks, guys.

David Archibald is the author of American Gripen: The Solution to the F-35 Nightmare