Aging bonobos need reading glasses too: study

Just like chimpanzees, bonobos are one of human's closest primate relatives and they obviously don't read. But researchers reported Monday that as these animals age, they could need a good pair of reading glasses too.

A new study published in the U.S. journal Current Biology found that aging bonobos often have difficulties in seeing things up close and that this long-sightedness is most evident as older bonobos engage in grooming their peers.

The older these animals get, the longer they stretch their arms from the rest of their bodies as they groom, it said.

"We found that wild bonobos showed the symptoms of long-sightedness around 40 years old," study author Heungjin Ryu of the Primate Research Institute of Kyoto University, said in a statement.

"We were surprised that the pattern found in bonobos is strikingly similar to the pattern of modern humans. This suggests that senescence of the eyes has not changed much from the Pan-Homo common ancestor, even though the longevity of modern humans is far longer than that of chimpanzees and bonobos."

Ryu said that researchers had already noticed this trend of older bonobos needing longer distances for grooming before but it's just that no one paid much attention to it, which they believed this long-sightedness was caused by a decline in the refractive power of the crystalline lens with age.

To learn more, the researchers used digital photographs to measure the grooming distance of 14 wild bonobos of various ages, ranging from 11 to 45 years old.

The measurements showed that the grooming distance increased exponentially with age. In one case, an old video of one of the bonobos enabled them to show that his eyesight had worsened over time.

"The results we found were very surprising even for us," Ryu said. "When I started to collect data, I did not expect that age could be such a strong predictor of long-sightedness."

The researchers said that long-sightedness might hinder the social lives of older individuals, explaining why older individuals aren't favored when it comes to selecting grooming partners.

People who grow long-sighted with age also have particular trouble seeing in the dark, Ryu said. That could be a big challenge for the bonobos that live in the shade of the rainforest canopy.

As for us humans, the findings in our bonobo relatives suggest that long-sightedness isn't a consequence of the modern lives we lead and all that time spent reading or staring at a screen, Ryu said. Rather, it's a natural process of aging rooted deep in our past.

The researchers planned to continue studying aspects of aging in bonobos to learn more about them and us. Enditem