A publication of the Archaeological Institute of America
Looking at apes, tools, and human evolution
Many animals have been observed using tools: Dolphins use sponges when fishing, crows use sticks to forage for insects in dead wood, capuchin monkeys use stones to break open nuts.
Apes use tools. So what? What does that tell us about human evolution? As it turns out, observing our closest living relatives as they wield stone hammers and manipulate gadgets can show us how early humans may have been using artifacts. It may even hold the key to the origins of culture, but too much extrapolation in this direction leads to vehement debate within the field of primatology.
Chimpanzees in Ivory Coast's Tai National Park use stone hammers to exert the 1100 kg of force needed to crack open panda nuts, according to a 2002 Science study published by archaeologist Julio Mercader. The chimps find the stones, carry them to processing stations, lay the nut on an anvil and crack it. Chimps have been observed cracking 100 nuts a day, wearing down the stone hammers with pitting and flaking.
By excavating an abandoned nut-cracking area, Mercader was able to compare the chimps' accidentally produced flakes with Oldowan flakes produced by hominins. Their similarities suggest that the earliest hominins could have been using the same technology to eat hard objects. But more importantly, the flake by-products of percussive nut-cracking action could have become the first cutting tools.
"Because we will never know directly what our ancestors were up to until we invent a time machine, we can only infer from the artifacts," says William McGrew, professor at the Lever Hulme Center for Human Evolutionary Studies at University of Cambridge and author of The Cultured Chimpanzee. "But in chimps, we have both the artifacts and the behavior."
"When we find hammer stones in the Oldowan we can guess what they were used for or we can look at chimps and what they use them for to give us some ideas, to help us interpret what we find," says McGrew.
Researchers can learn about chimpanzee "culture" by tracking nut-cracking behavior. Cracking nuts is no easy feat, and it can take a chimpanzee up to seven years to learn how to do it correctly. The technology is passed from generation to generation and diffuses across populations.
For that reason, it was significant when, 1,000 miles east of Mercader's chimpanzee population, across the N'Zo-Sassandra River and the entire country of Nigeria, Bethan Morgan and a team of researchers recently observed chimpanzees using the same technique to crack nuts in the forests of Cameroon. The discovery, reported in Current Biology, is surprising because the information barriers of river and distance suggests that the technology developed independently.
"We don't have any real sense of how often innovations occur in chimpanzee society," says McGrew. "It certainly doesn't happen frequently, in the sense that you can study chimps for years and years and never see it."
Sometimes differences in tool use can be more informative than similarities. In a laboratory study published in Nature, Andrew Whiten taught two chimpanzees different methods of extracting food from identical machines. Using sticks, one learned how to poke a lever and the other learned how to lift a lever. When the two chimpanzees were re-introduced to two different groups of chimpanzees, all but 2 of the 32 chimpanzees in the study learned how to extract food from the device.
More surprisingly, some chimpanzees independently learned the alternate method of extracting food, but continued to use the method used by their companions anyway. This apparent conformity bias within the group is a basic element of human culture.
"When we find chimpanzees living in very similar habitats, possibly even next door to each other geographically, and yet they have different elementary technology repertoires, we tend to believe there's something more than just environmental determinism happening there," says McGrew. He explains that the experiment implies social learning, the basis of culture.
So, do chimpanzees have culture? That depends on how culture is defined. Some researchers believe culture is linked to symbolic meaning, a concept only humans are known to have mastered. Others, like McGrew, favor a broader definition: "Socially learned patterns that are characteristic of a community or a population and handed down from one generation to the next." That is what chimps have.
So chimpanzees, humans' closest living relative, may have a basic capacity for culture, but how far back does this culture instinct go?
In a Science article, Carel van Schaik reports observing geographic variations in orangutan behavior that could be considered culture. For her study, van Schaik broke the characteristics of culture down into four sub-sections: 1. labels, "where food preferences or predator recognition are socially induced," 2. signals, socially transmitted vocalizations or displays, 3. skills, innovations like tool use that are learned by the group, and 4. symbols, "probably derived from signal variants that became membership badges of the social unit or population."
Only humans have all four elements of culture, but chimpanzees and, now, orangutans have been observed to exhibit the first three. "The presence in orangutans of humanlike skill (material) culture pushes back its origin in the hominoid lineage to about 14 million years ago, when the orangutan and African ape clades last shared a common ancestor, rather than to the common ancestor of chimpanzees and humans," says van Schaik.
But Robert Sussman, primatologist at Washington University in St. Louis and author of The Biological Basis of Human Behavior, doesn't believe it's possible to separate the idea of culture from the uniquely human ability to use symbolism.
For example, two chimpanzee populations living on opposite sides of Africa would only have minor differences in tool use, diet, and behavior, often related to ecology. On the other hand, two human populations, even if they're living in the same African valley, could have completely different world views.
"What they eat, who they marry, who's their enemy, what they wear, their view of the Earth and how it was created, their language, everything is different," says Sussman. "So what humans do is they create their world through a filter of culture. And the difference is so great between that sort of symbolized created culture and the differences that we find in chimpanzees in their whole range, that to call the two things the same thing trivializes all of anthropology."
As far as tool use goes, Sussman agrees that observing ape behavior can show us how early humans probably used tools. In fact, the archaeological record shows that early humans were all using about the same tool technology until about 40 to 60 mya. That is when, Sussman says, true culture first emerged; when paintings, amulets and burials indicate that humans were capable of symbolic views and there were distinctions between humans living in different locations.
So, apes use tools. And, by observing apes using tools, we gain a better understanding of the development of tool technology and the way in which human ancestors may have once used tools. The extent to which tool use can or should be used as a way to gauge or define culture is debatable. We always try to see ourselves in our closest relatives, to interpret ape behavior as an underdeveloped equivalent of our own. But in the end, they are just apes, and we are only human.
Kirsten Vala received her B.A. in psychology and anthropology at Washington University in St. Louis and is currently a journalism graduate student at New York University.