No Grumpy Old Men in the Chimp World

Dr. Rosati, Dr. Machanda and their colleagues looked at several aspects of male chimp behavior as recorded in more than 20 years of almost daily observations, with 78,000 hours of observations on 21 male chimpanzees from age 15 to 58. They used the proximity of chimpanzees to one another to determine friendships — friends sit together. And they used grooming to decide whether the friendships were mutual, with each chimp paying attention to the other, or one-sided.

As they got older, the chimps developed more mutual friendships and fewer one-sided friendships. They also exhibited a more positive approach to their whole community, continuing grooming of other chimps, including those that weren’t close friends, at the same rate, but with a drop in aggression. Other primates don’t necessarily follow this pattern as they grow older, according to the authors. Some monkeys tend to withdraw from social relationships and their aggression levels stay high.

Of course, this can also happen in humans, but the data indicate that Aunt Ratchet and Uncle Vlad are exceptions.

The data analysis required for such studies is what happens after the field observation. Anyone who watches nature television shows can probably call to mind the image of Jane Goodall amid the Gombe chimps, or other similar, apparently idyllic portraits of field biologists.

Dr. Machanda said that people may think it’s just a matter of using an Excel spreadsheet. But she said that Excel won’t accept data “after something like 168,000 rows.”

“For most people, that would be insane to have a table that has that many rows, but actually I think in our database, our largest table has something like 4.7 million rows of data,” she added, with “dozens and dozens of tables.”

Dr. Gilby, who manages 60 years of data from the Gombe project, going back to the days when, he said, it was piling up in paper form at Dr. Goodall’s house in Dar es Salaam, said the new work demonstrated the importance of long-term studies.