Aside from having a distant evolutionary ancestor, humans and monkeys have one thing in common: when both grow into old age, they become more selective with friends.
You may have observed this behavior among your grandparents or your retiring parents. Some of them may opt to go alone on the same diner on the same days every week, some may get too cranky around strangers and some may prefer to watch TV by themselves.
New research suggests that the same behavior occurs in monkeys, particularly in Barbary macaques. These animals tend to become less sociable as they age, just like humans. The question is: why?
Monkey Behavior
Scientists from the German Primate Center wanted to know how age affected the behavior of more than 100 Barbary macaques kept in an enclosure in a park in France.
They investigated how the monkeys - whose ages ranged from 4 to 29 years (equivalent to 105 human years) - reacted to physical objects such as novel toys and tubes with food, social interactions such as fighting and grooming "friends" and new social information, such as calls and photos of "friends" and "strangers."
Researchers discovered that the interest of Barbary macaques in toys wane when they become adults. At around 20 or the retirement age of monkeys, these animals approached fewer monkeys and had less social contact.
What surprised scientists is that this obvious withdrawal was not prompted by a social affinity to avoid old monkeys. Younger ones still groomed and approached their elders.
It also wasn't because older monkeys were not interested in anything at all. Scientists found that older monkeys still hissed to others during fights and still responded to photos of others.
These older monkeys are still attuned to what is going on around them, but they do not want to participate, says Julia Fischer, one of the researchers of the study.
Deep Root In Evolution?
The dominant psychological theory that could explain why this behavior happens in humans is that they want to maximize the time they have left with death on the horizon.
Fischer says although monkeys have excellent memories, there is no evidence that they are self-aware about their impending deaths. So if both monkeys and humans act this way as they age, the theory may be rationalizing a natural behavior with biological roots, she says.
Alexandra Freund, Fischer's co-researcher, says the findings of the study clearly tell us that we are not distinctive in how we grow into old age.
"There might be an evolutionary 'deep' root in this pattern," says Freund.
Fischer says whatever the reason for the similarity in behavior, the main takeaway from the research is that although how we act is much the result of our choice and deliberation, it might be more similar to our primate ancestors than we believe.
Details of the study are published in the journal Current Biology.
Photo: Scott Wylie | Flickr
