A team of researchers has found evidence of long-sightedness in wild bonobos, close ancestors of humans. The bonobos in the study showed signs of presbyopia as they aged. The findings may help scientists better understand the aging process in humans and other primates. The details are in a paper that was just published in the journal Current Biology.
Presbyopia, also called farsightedness or long-sightedness, is an age-related disorder of the eyes. As humans age, they may begin to have trouble focusing their eyes on nearby text and objects. This process often starts in the 40s or 50s, gradually becoming worse as the person gets older. Currently, there is no cure available. Presbyopia is usually treated with special prescription eyeglasses or contact lenses. While this form of long-sightedness is very common in humans, scientists had yet to study the disorder in nonhuman primates.
Bonobos (Pan paniscus) are close relatives of common chimpanzees and humans. Although their exact wild lifespan is unknown, bonobos can live to be over 40 years old. Effects of aging had not been studied in the species though there was anecdotal evidence of presbyopia in older apes. A few older bonobos had been spotted grooming their peers at awkwardly longer distances when compared to younger animals. This led researchers to conduct a controlled experiment using observational data of wild bonobos.
The research team collected data from 14 wild bonobos ranging in age from 11 to 45 years. The team took photographs of the apes during grooming sessions to record grooming distances. The distance data was then compared with factors such as age and sex. The researchers found no difference in grooming habits between male and female bonobos. The team did find a link between age and grooming distance, however. Older bonobos groomed their partners from a greater distance, only getting close when necessary. The differences were significant enough for the authors to conclude that the aging bonobos showed symptoms of presbyopia.
The team’s findings provide evidence for the development of age-related long-sightedness in older bonobos. This goes against theories that attribute presbyopia to the human lifestyle. Instead, it appears to be a natural part of aging in great apes.
Ryu et al. Long-sightedness in old wild bonobos during grooming. Current Biology (2016).