Tag Archives: chimps

Chimps can hunt with tools, but why doesn’t it happen more often?

You’d think we’d know a bit more about our closest living relatives in the animal kingdom – but we’re still making surprising discoveries about chimpanzees, whose genome is about 96 percent similar to ours. While its been known for over a century that chimps are capable of making tools, it turns out that in the last few years, at least one particular tribe of the primates located in Senegal. Back in 2007, anthropologist Jill Pruetz first reported that the savanna chimps at her research site in Fongoli, Senegal, had begun using tools in order to hunt their prey. While this discovery on its own was a startling find, as Pruetz began studying them more in depth, she learned that the female chimps were the predominant hunters in the group who took up the tools.

Due to the small sample size many dismissed the findings but Pruetz, who teaches at Iowa State University, set out to learn more. Along with her researchers, she documented well over 300 different tool-assisted hunts. This also comes on the heels of evidence that a number of primates are also capable of migrating for long distances, during which they call out to their companions to signal changes in direction. The researchers’ results were published this week in the latest issue of the journal Royal Society Open Science, and are supportive of Pruetz’s initial discoveries – that when they hunt, the female chimps will use tools more often than males will.

Although adult male and female chimps will often hunt side by side, the males typically capture their prey by hand. Researchers, however, have observed that both the male and female chimps have made use of tools, but that in over half of the hunts – 175 versus 130 – the tools were used by females. Despite the fact that males made up roughly 60 percent of the hunting group, only about 40 percent of the hunts using tools were done by the males.

Although the sample size was small, Pruetz suggests that there’s likely a great deal of diversity to be found when it comes to chimp behavior – factors that could easily change depending on the environment in which they’re found.

“It’s just another example of diversity in chimp behavior that we keep finding the longer we study wild chimps,” Pruetz said. “It is more the exception than the rule that you’ll find some sort of different behavior, even though we’ve studied chimps extensively.”

The targets of these hunts for the chimps, both male and female, were typically galagos, also known as bush babies, in the tool-assisted hunts. They’re a more primitive, nocturnal species of tree-dwelling primates. Their cries sound similar to human infants and they mark tree branches with urine, allowing them to sniff out and land on the same tree branches each time. According to Pruetz, the chimps are capable of fashioning spear-like tools that they use to jab at the animals when they spot them lurking within the cavities of trees at night. She suggests that this observable difference between how the genders hunt is that the males tend to be more optimistic when finding their quarry.

“What would often happen is the male would be in the vicinity of another chimp hunting with a tool, often a female, and the bush baby was able to escape the female and the male grabbed the bush baby as it fled,” Pruetz said.

Another significant question is why are only the savanna chimps found in Fongoli the only known population of non-humans that routinely stalks prey using tools. Some South American marmosets have been known to fish for clams in the Amazon and break the shells open with rocks – a learned behavior that the adults pass to their offspring, but these chimps design tools specially for the occasion. So what’s the reason? Pruetz says maybe it’s the wrong one to be asking. Instead, we should probably be asking why the chimps at other sites are not using this technique. It’s prossible that they don’t simply because that they never learned the technique, she said. Tool hunting could be the product of a gradual social tolerance that has not yet developed at the other chimp sites. Perhaps if there were a greater population of chimps, living in larger societies, they would have advanced to this capacity.

“At Fongoli, when a female or low-ranking male captures something, they’re allowed to keep it and eat it. At other sites, the alpha male or other dominant male will come along and take the prey. So there’s little benefit of hunting for females, if another chimp is just going to take their prey item.”

The environment could be another important factor. Pruetz noted that there was a lack of red colobus monkeys, the preferred prey for chimps found at other sites, largely due to the dry conditions found at Fongoli. The bush babies are more prevalent instead at Fongoli, and other types of prey that the female chimps are able to access with the use of tools.

Pruetz, who is a National Geographic Emerging Explorer, has often been asked why the female’s use of tools is considered an attribute of hunting rather than one of gathering. This is a question that is reflective of the stereotypes associated with the behavior of female chimps. Chimps were first seen using sticks to “fish” for termites back in the late 19th century, but according to Pruetz, the comparison between catching ants or termites with a stick and tool-assisted hunting are superficial. The behavior of the prey and effort required by the hunter is different.

“Fishing for termites is a very different activity than jabbing for a bush baby,” Pruetz said. “With fishing, termites grab on to a twig and don’t let go and the chimp eats the termites off the twig. When hunting, the bush baby tries to bite, escape or hide from the chimp. The chimps are really averse to being bitten by a bush baby.”

Although a bush baby may be smaller than and not as fierce as a red colobus monkey, Pruetz maintains that this is really no different than humans preferring to hunt doves rather than deer. Ultimately, the tool-assisted hunting allows the female chimps, which could be less likely to run down their prey, access to a nutrient rich food source, according to Pruetz.

James Sullivan
James Sullivan is the assistant editor of Brain World Magazine and a contributor to Truth Is Cool and OMNI Reboot. He can usually be found on TVTropes or RationalWiki when not exploiting life and science stories for another blog article.

Explaining Why We Have Such Big Brains in Just a Few Letters

G, C, A, T to be exact. Only a slight stretch of our DNA make the difference between us and our chimpanzee cousins. When embedding the bit of genetic information into mice, scientists found that the rodents’ brains grew significantly larger than usual.

“It’s likely to be one of many DNA regions that’s critical for controlling how the human brain develops,” says Debra Silver, on the region they chose. Silver is a neurobiologist at Duke University Medical School.

It is likely that this accounts for the massive difference in brain size between humans and our closest living relative, the chimpanzee – a difference of anywhere between two and four times larger by current estimates. While also having larger brains, people also have many more neurons than their simian friends, and many more connections, or synapses, occurring between each.

Scientists have long sought to determine what genetic basis we have for abstract thought as well as valuing logic and complex emotions – our capacity to develop languages and artwork, concepts that have long been associated with larger brain size. Currently, we have a wealth of evidence that our fellow hominids the Neanderthals were also capable of artwork and tool making, presenting a rather different picture than our old stereotypes of mindless barbarians. The Human Genome Project, concluded in 2004, revealed that humans and chimpanzees have DNA approximately 95 percent identical, establishing that we have more in common with chimps than mice do with rats. Silver’s latest interest, however, is to learn more about those regions in the genome that differ. Chimps do have capacity for tool making, using straw to catch termites, but their linguistic capacity, aside from facial reading, is still being explored.

Silver and her researchers isolated a gene that aids in brain development and removed the DNA region near it, which they proceeded to plant into mice. One group received human DNA, and the other received DNA extracted from chimps.

“What we discovered is that the human DNA turned on gene activity in neural stem cells, and these are cells which produce the neurons of our cerebral cortex,” said Silver.

The mice that were born yielded brains 12 percent larger than the brains of mice who received chimp DNA. The findings were published in Current Biology.

Now, Silver’s team will begin an investigation of how differently mice with larger brains will behave as they mature, knowing that they have only begun to scratch the surface. At the same time, they are looking for other genes that are specific to humans.

Of particular interest is within a vestigial genetic region known popularly as “junk DNA,” that which evidences our common descent from other, more primitive lifeforms, but until recently was believed to serve no specific purpose of its own, since this region doesn’t code for any active proteins in the body. Currently, however, researchers suspect that this region is critical for turning on and off genes as new cells are formed. Their ultimate function, if any at all, still remains a mystery.

“We have very little scientific information about the actual functions of those regions,” said Katie Pollard, who researches human and chimp DNA from the University of California, San Francisco, in a recent interview with NPR.

Many of the ways in which we differ from chimps can be found within the junk DNA, and many researchers like Pollard are still looking to meet that gap. As impressive as the results reported in the study may have been, it is difficult to predict what effect it may have on the mice. It’s preferential to see directly how either people or chimps are affected by the region’s presence, but then the research touches on ethical grounds.

“We’re talking about humans and chimpanzees here, and you cannot experiment on either of those,” notes Pollard. “And so it’s very challenging to prove causation.”

Challenging, sure, but not necessarily impossible either. Already, Pollard and her colleagues are experimenting with lab cultivated cells from chimps and humans, raised in Petri dishes.

“We can now actually generate the equivalent of embryonic brain cells and tissues that are human or chimpanzee,” says Pollard. “And, using genome engineering techniques, we can start to study the effects of switching the human and the chimp sequences in these primate cell lines.”

As their work progresses, the team hopes that soon they may find specific sequences in the DNA that are human by their very definition – opening the gateway of questioning precisely what characteristics make us human, and how distinct we really are from our living primate relatives. The difference may be far less than we ever imagined.

James Sullivan
James Sullivan is the assistant editor of Brain World Magazine and a contributor to Truth Is Cool and OMNI Reboot. He can usually be found on TVTropes or RationalWiki when not exploiting life and science stories for another blog article.