The trend of aborting babies in the face of strange males is known as the Bruce effect. That’s not a slight against men of that name; the effect is named after the scientist who discovered it – Hilda Margaret Bruce. In 1959, she noticed that pregnant mice will abort if they’re exposed to unfamiliar males. Since then, scientists have found the same effect among other laboratory rodents, and domestic horses. But the Bruce effect has always remained a quirk of captivity. No one really knew if wild animals do the same thing.
A new study found that geladas, a relative of the baboon, do have abortions in the wild:
Normally, the failure rate for gelada pregnancies is around 2 per cent. If a new male arrives, it shoots up to 80 per cent. … But why would a pregnant female abort her own foetus? Roberts thinks that it’s an adaptive tactic in the face of a new male’s murderous tendencies. Since the male would probably kill the newborn baby anyway, it’s less costly for the female to abort than to waste time and energy on bringing a doomed infant to term. Her future offspring, conceived more quickly and fathered by the incumbent king of the hill, will stand a better chance of survival.
(Photo of a gelada in the Simien Mountains of Ethiopia by Flickr user M. Bos)