Living Links: Near and Far

An article published December 4th reported the first observations of chimpanzees using tools to dig up tubers for consumption. Digging for food is a remarkable behavior on many levels, but primarily I believe it captures our imagination because we immediately connect this behavior with its ultimate application by humans: agriculture. The discovery by Hernandez-Aguilar, Moore, and Pickering was made by observing tell-tale indirect evidence of the behavior: sticks with dirt on one end, holes, wadges of chewed tubers, and chimpanzee knuckle-prints, feces, and nests. Think CSI: Tanzania.

These chimpanzees live in a region that is a mixture of forest and grassland with highly seasonal rainfall. The habitat is believed to be both the limit of what chimpanzees can tolerate, and similar to what early hominins at one point occupied. The thought process is that since our early human ancestors made the transition from forests to grasslands, discoveries like this one offer a glimpse into what behaviors these ancestors may have been capable of, and thus how this transition may have begun. As fascinating as this discovery is, many of the conclusions and implications for human evolution were already known from a different source, un-cited by the authors, several thousand miles and many millions of years of evolutionary time away.

Three years ago scientists in Brazil directly observed and videotaped capuchin monkeys digging for tubers using stones. De A. Moura and Lee were the first to observe an animal, any animal, using tools to dig up food outside of humans. What can the behavior of a monkey, with whom we diverged roughly 35-40 million years ago, tell us about human evolution? Well, quite a bit, actually. The capuchin monkeys observed digging live in a dry forest with highly seasonal rainfall at the limit of what this species is believed to tolerate (sound familiar?). The authors of the chimpanzee study conclude that digging for tubers “need not have required a technology that preserved in the archaeological record,” This is in reference to the stick tools used by chimpanzees, but the unmodified stone tools used by capuchin monkeys already demonstrated that. Hernandez-Aguilar and co-workers also say “the discovery that savanna chimpanzees use tools to obtain USOs [underground storage organs, jargon for tubers] shows that such consumption was within the grasp of chimpanzee-like hominins.” Again, this was implied by the capuchin monkeys doing the same, as it demonstrated that the behavior could evolve without modern human-sized brains.

Most importantly, the authors “argue that chimpanzees adapting to such extreme (for them) conditions can be used as models for investigating particular aspects of early hominin behavioral ecology.” It seems appropriate to add capuchin monkeys to that statement. Why? Analogous (or convergent) evolution, when unrelated species independently evolve similar adaptations, can be just as informative as homologous evolution, when adaptations share a common origin. The conditions under which the separate behaviors evolved may be similar, and thus informative, especially when examples from close living relatives are not known or do not exist. In our desire to fully understand human origins, we must not focus only on our closest relatives for answers. The Living Links to our past are all around us; we only need look for them.

–Matthew Campbell

Video of a capuchin digging for tubers

Full references to the articles mentioned:

de A. Moura, A. C., & Lee, P. C. (2004). Capuchin Stone Tool Use in Caatinga Dry Forest. Science, 306(5703), 1909.

Hernandez-Aguilar, R. A., Moore, J., & Pickering, T. R. (2007). Savanna chimpanzees use tools to harvest the underground storage organs of plants. Proceedings of the National Academy of Sciences, 104(49), 19210-19


Wiz-kid outperforms his elders

Reports of youngsters outperforming their elders in computers games would not normally be worthy of headline news. Urban mythology is full of amusing tales of grandparents who use their computer CD drawer as a convenient cup-holder, or press the ‘help’ button on their keyboard and sit by the phone for days waiting for a response. But what if the report involved chimpanzees, and not ipod-savvy middle-schoolers with blue-tooth cell phones?

In a new study published in Current Biology (Vol. 17, p1004) Inoue & Matsuzawa found that Ayumu, a 5-year-old chimpanzee, could outperform both his mother, and a group of university students in a computer task designed to investigate working memory. In the study, participants saw 5 Arabic numerals (from a set of 1 through 9) presented in a random location on a touchscreen monitor. The aim of the task was to touch each numeral in the correct ascending order. But, there was a catch. The numbers appeared on the screen for only a fraction of a second before being replaced by a white square; so fast, in fact, that the presentation was ‘subliminal’. Ayumu was quicker and more accurate than either his mom or the humans, demonstrating a phenomenal ability for symbol recall and working memory. The authors discuss their findings in relation to the evolution of language and symbolism.

See Ayumu perform here.

View more video clips from the Kyoto Primate Research Institute website here.

For me, the findings of this study have additional implications for how we conduct comparative studies of cognition. Many cognitive studies are motivated by evolutionary questions about whether other species share the same cognitive abilities as us. However, because such studies are often intrinsically human-centric, they tend to utilize methodologies that inadvertently favor humans while posing handicaps for the apes. However, the studies we conduct at the Living Links Center involve chimps learning from fellow chimps, and in these more natural conditions we find that this is something they are rather good at, in fact so good that they have developed their own distinct cultures. The study by Inoue & Matsuzawa is particularly interesting because it is initiated from an unusual perspective: rather than asking whether chimpanzees can do what we do, the authors have taken a skill at which their chimpanzees were particularly good and then ask if we can do what they do. It seems that when the tables are turned like this, we don’t always come out on top. For me, this study highlights the importance of casting a wide net when searching for cognitive abilities within the animal kingdom. If we only ever study other species to see if they share our cognitive abilities, we may miss important features of their cognition and learn little about abilities we may have lost.

Ayumu trounces British memory champion!

Click here for more studies in which chimpanzees outperformed humans.

Think you can do better than a chimp? Give it a try here!

–Victoria Horner

Introducing the Living Links Blog

Welcome to the blog of the Living Links Center, which will serve to introduce new findings, new insights, field reports, and personal reactions to items in the news that relate to primate research and human evolution.

— Frans de Waal