It’s amazing what chimpanzees will do for a snack.
In Congolese rainforests, the apes have been known to poke a hole into the ground with a stout stick, then grab a long stem and strip it through their teeth, making a brush-like end. Into the hole that lure goes, helping the chimps fish out a meal of termites.
How did the chimps figure out this sophisticated foraging technique and others?
“It’s difficult to imagine that it can just have appeared out of the blue,” said Andrew Whiten, a cultural evolution expert from the University of St. Andrews in Scotland who has studied tool use and foraging in chimpanzees.
Now Dr. Whiten’s team has set out to demonstrate that advanced uses of tools are an example of humanlike cultural transmission that has accumulated over time. Where bands of apes in Central and East Africa exhibit such complex behaviors, they say, there are also signs of genes flowing between groups. They describe this as evidence that such foraging techniques have been passed from generation to generation, and innovated over time across different interconnected communities.
In a study published on Thursday in the journal Science, Dr. Whiten and colleagues go as far as arguing that chimpanzees have a “tiny degree of cumulative culture,” a capability long thought unique to humans.
From mammals to birds to reptiles and even insects, many animals exhibit some evidence of culture, when individuals can socially learn something from a nearby individual and then start doing it.
But culture becomes cumulative over time when individuals learn from others, each building on the technique so much that a single animal wouldn’t have been able to learn all of it on its own. For instance, some researchers interpret using rocks as a hammer and anvil to open a nut as something chimpanzees would not do spontaneously without learning it socially. Humans excel at this, with individual doctors practicing medicine each day, but medicine is no one single person’s endeavor. Instead, it is an accumulation of knowledge over time.
Cassandra Gunasekaram, a doctoral candidate in evolutionary biology at the University of Zurich, spotted a pattern when she pored over a genetic data set of 35 populations of chimpanzees in East and Central Africa, and then compared it with information about their use of tools.
Most chimpanzee populations do not use a complex set of tools, in a specific sequence, to extract food.
But some regularly do. And these groups are likely to be genetically related. They are also likely to be related to populations where only preliminary components of sophisticated tool set sequences are used. For instance, groups that just poked a hole into the hard ground with a thick stick to get underground critters, but didn’t go as far as using a lure.
The populations of chimpanzees that use no tools or simple tools to get food aren’t as closely genetically related, the study suggests.
This genetic contrast among tool-using apes suggests that sophisticated foraging tricks “might need some sort of social transmission and social learning, an exchange of ideas between different places,” and improvement and innovation over time, Ms. Gunasekaram said.
Sexually mature female chimps may be culture bearers, the researchers posited. They migrate to other groups to reproduce. That has made even distant populations related.
These findings suggest that the “modestly cumulative culture” of chimpanzees depends on migration between local populations, where mingling allows for social learning, said Peter Richerson, an expert in cultural evolution from the University of California, Davis, and an author of a perspective accompanying the study.
The research also helps upend the assumption that only humans have cumulative culture. Chimpanzees do too, just less of it. And this may help explain how humans came to have such a complex cumulative culture in the first place.
While the study uses genetic information to help understand chimpanzee social relationships, Claudio Tennie, an ape culture expert from the University of Tübingen in Germany, questioned whether it offers evidence of humanlike cumulative culture. It’s still uncertain whether the tricks the chimpanzees are using are so sophisticated they couldn’t have been independently invented by individuals in different groups, Dr. Tennie said.
He said experiments he and others have worked on suggest chimpanzees could come up with a stick-and-lure technique without learning it from others. And studies suggest orangutans and capuchin monkeys spontaneously use rocks in sequence to crack nuts open without social learning.
Always attributing complex skills to social culture “kind of presupposes that the apes are not clever on their own,” Dr. Tennie said. “What I’ve been saying for all these years is ‘You’re underestimating the apes’ cleverness!’”
Dr. Whiten counters that his experiments, like the one where he gave chimpanzees complicated straws to drink juice, offer “circumstantial evidence” that these behaviors are “only really achieved” and spread by cultural transmission.
While it might be an open question how chimpanzees learned those sophisticated tricks, it’s clear that some go to great lengths to get a snack.
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