The scientific study of animal behavior has meant, among other things, that humans have had to accept that they are not the only animals that use tools, show emotions and recognize themselves in a mirror.
Still, it's a bit strange to see aging bonobos looking as if they need reading glasses. They aren't trying to decipher the small-print ingredients for over-the-counter pain relievers. They're trying to find the itty-bitty lice in each other's fur, so they can do their neighborly and familial grooming duty, and have a snack.
Heungjin Ryu and colleagues from Kyoto University in Japan and the University of St. Andrews in Scotland recorded 14 bonobos grooming each other at the Luo Scientific Reserve in the Democratic Republic of Congo, where the apes have been part of a decades-long study.
As the scientists reported recently in Current Biology, the videos show that grooming distance -- how close the nitpicking ape gets to the ape being groomed -- increases with age much the way aging humans move back a bit from whatever they're trying to see. For apes, nitpicking puts similar demands on the eyes.
Ryu, a doctoral student, said that what seemed to be farsightedness in older bonobos had been noticed before but not rigorously studied.
The scientists knew the ages of the bonobos they were recording, so they just had to get accurate distance measurements. They did this by first photographing the ears of each animal and then photographing a ruler at the same distance. That let them come up with an ear length, which they used to calculate the distance from eye to louse.
The scientists found that the grooming distance didn't change based on the sex of the bonobos or how closely they were related. But it changed with age very much the way that human sight changes.
Age-related farsightedness is thought to be caused by changes in the eye's lens and muscles.
In an odd side note in the published paper, the authors pointed out that another sign of aging in humans does not appear in bonobos. Human ears get longer as we age. The ears of bonobos do not.
ActiveStyle on 12/19/2016