For First Time, Chimps Seen Making Weapons for Hunting

SOURCE: The Washington Post

AUTHOR: Rick Weiss, Washington Post Staff Writer

COMMENTARY: Allen MacNeill

Friday, February 23, 2007: Chimpanzees living in the West African savannah have been observed fashioning deadly spears from sticks and using the tools to hunt small mammals — the first routine production of deadly weapons ever observed in animals other than humans. The multistep spearmaking practice, documented by researchers in Senegal who spent years gaining the chimpanzees' trust, adds credence to the idea that human forebears fashioned similar tools millions of years ago. The landmark observation also supports the long-debated proposition that females — the main makers and users of spears among the Senegalese chimps — tend to be the innovators and creative problem solvers in primate culture.

Using their hands and teeth, the chimpanzees were repeatedly seen tearing the side branches off long, straight sticks, peeling back the bark and sharpening one end. Then, grasping the weapons in a "power grip," they jabbed them into tree-branch hollows where bushbabies — small, monkeylike mammals — sleep during the day. In one case, after repeated stabs, a chimpanzee removed the injured or dead animal and ate it, the researchers reported in yesterday's online issue of the journal Current Biology.

"It was really alarming how forceful it was," said lead researcher Jill D. Pruetz of Iowa State University, adding that it reminded her of the murderous shower scene in the Alfred Hitchcock movie "Psycho." "It was kind of scary."

The new observations are "stunning," said Craig Stanford, a primatologist and professor of anthropology at the University of Southern California. "Really fashioning a weapon to get food — I'd say that's a first for any nonhuman animal."

Scientists have documented tool use among chimpanzees for decades, but the tools have been simple and used to extract food rather than to kill it. Some chimpanzees slide thin sticks or leaf blades into termite mounds, for example, to fish for the crawling morsels. Others crumple leaves and use them as sponges to sop drinking water from tree hollows.

But while a few chimpanzees have been observed throwing rocks — perhaps with the goal of knocking prey unconscious, but perhaps simply as an expression of excitement — and a few others have been known to swing simple clubs, only people have been known to craft tools expressly to hunt prey.

Pruetz and Paco Bertolani of the University of Cambridge made the observations near Kedougou in southeastern Senegal. Unlike other chimpanzee sites currently under study, which are forested, this site is mostly open savannah. That environment is very much like the one in which early humans evolved and is different enough from other sites to expect differences in chimpanzee behaviors.

Pruetz recalled the first time she saw a member of the 35-member troop trimming leaves and side branches off a branch it had broken off a tree.

"I just knew right away that she was making a tool," Pruetz said, adding that she suspected — with some horror — what it was for. But in that instance she was unable to follow the chimpanzee to see what she did with it. Eventually the researchers documented 22 instances of spearmaking and use, two-thirds of them involving females.

In a typical sequence, the animal first discovered a deep tree hollow suitable for bush babies, which are nocturnal and weigh about half a pound. Then the chimp would break off a branch — on average about two feet long, but up to twice that length — trim it, sharpen it with its teeth, and poke it repeatedly into the hollow at a rate of about one or two jabs per second. After every few jabs, the chimpanzee would sniff or lick the branch's tip, as though testing to see if it had caught anything.

In only one of the 22 observations did a chimp get a bush baby. But that is reasonably efficient, Pruetz said, compared with standard chimpanzee hunting, which involves chasing a monkey or other prey, grabbing it by the tail and slamming its head against the ground.

In the successful bush-baby case, the chimpanzee, after using its sharpened stick, jumped on the hollow branch in the tree until it broke, exposing the limp bush baby, which the chimp then extracted. Whether the animal was dead or alive at that point was unclear, but it did not move or make any sound.

Chimpanzees are believed to offer a window on early human behavior, and many researchers have hoped that the animals — humans' closest genetic cousins — might reveal something about the earliest use of wooden tools. Many suspect that the use of wooden tools far predates the use of stone tools — remnants of which have been found dating from 2.5 million years ago. But because wood does not preserve well, the most ancient wooden spears ever found are only about 400,000 years old, leaving open the question of when such tools first came into use. The discovery that some chimps today make wooden weapons supports the idea that early humans did too — perhaps as much as 5 million years ago — Stanford said.

Adrienne Zihlman, an anthropologist at the University of California at Santa Cruz, said the work supports other evidence that female chimps are more likely than males to use tools, are more proficient at it and are crucial to passing that cultural knowledge to others.

"Females are the teachers," Zihlman said, noting that juvenile chimps in Senegal were repeatedly seen watching their mothers make and hunt with spears.

Females "are efficient and innovative, they are problem solvers, they are curious," Zihlman said. And that makes sense, she added.

"They are pregnant or lactating or carrying a kid for most of their life," she said. "And they're supposed to be running around in the trees chasing prey?"

Frans B.M. de Waal, a primatologist at Emory University, said aggressive tool use is only the latest "uniquely human" behavior to be found to be less than unique.

"Such claims are getting old," he said. "With the present pace of discovery, they last a few decades at most."

COMMENTARY:

Yet another supposedly significant difference between humans and non-human animals falls by the wayside. It would be really interesting to know when this behavior first began, and where (and by whom). Based on what we already know about chimp learning behavior, it is very likely that a young female first tried this technique, possibly modeling it on the already well-developed technique of using a twig stripped of its branches to "fish" for termites in termite mounds. Also, it is likely that the technique has spread via imitation, rather than by directed learning. Chimps (like many other primates) are very good at imitative learning, but apparently do not actually "teach" each other how to do things...but maybe this will also be observed at some point in the future.

Furthermore, it is clear that the female chimps fashioning these spears are doing so intentionally: they perform a specific, learned behavior with the intent to use it to extract food (i.e. bushbabies) from locations that would otherwise be inaccessible. A clear case of "design" in a non-human animal, and clearly learned/based on experience (i.e. not innate/hard-wired). Anyone who argues that "design" or "intentionality" does not exist in nature is either deliberately self-deceived or stupid.

Does this mean that "design" is an intrinsic property of nature, however? Not at all; rather, it shows that "design" (i.e. intentional behavior) can be an emergent property of a particular class of natural entities. We know that we are capable of intentional behavior, and now we have solid evidence that chimps are as well. However, none of this is evidence for the kind of "intrinsic design" that "intelligent design theorists" propose as an explanation for the origin of complex adaptations. Rather, it is evidence for the kind of "emergent design" that Ernst Mayr explained as fully compatible with evolutionary theory more than thirty years ago.

--Allen

Unraveling Where Chimp And Human Brains Diverge

SOURCE: Terra Daily News

COMMENTARY: Allen MacNeill

Just in time for our discussion of human-chimpanzee differences in our evolution course at Cornell, here is an article describing recent research into how human an chimpanzee brains differ. Commentary follows:

Los Angeles CA (SPX) Nov 14, 2006: Many of the human-specific gene networks identified by the scientists related to learning, brain cell activity and energy metabolism.

Six million years ago, chimpanzees and humans diverged from a common ancestor and evolved into unique species. Now UCLA scientists have identified a new way to pinpoint the genes that separate us from our closest living relative - and make us uniquely human. The Proceedings of the National Academy of Sciences reports the study in its Nov. 13 online edition.
"We share more than 95 percent of our genetic blueprint with chimps," explained Dr. Daniel Geschwind, principal investigator and Gordon and Virginia MacDonald Distinguished Professor of Human Genetics at the David Geffen School of Medicine. "What sets us apart from chimps are our brains: homo sapiens means 'the knowing man.'

"During evolution, changes in some genes altered how the human brain functions," he added. "Our research has identified an entirely new way to identify those genes in the small portion of our DNA that differs from the chimpanzee's."

By evaluating the correlated activity of thousands of genes, the UCLA team identified not just individual genes, but entire networks of interconnected genes whose expression patterns within the brains of humans varied from those in the chimpanzee.

"Genes don't operate in isolation - each functions within a system of related genes," said first author Michael Oldham, UCLA genetics researcher. "If we examined each gene individually, it would be similar to reading every fifth word in a paragraph - you don't get to see how each word relates to the other. So instead we used a systems biology approach to study each gene within its context."

The scientists identified networks of genes that correspond to specific brain regions. When they compared these networks between humans and chimps, they found that the gene networks differed the most widely in the cerebral cortex -- the brain's most highly evolved region, which is three times larger in humans than chimps.

Secondly, the researchers discovered that many of the genes that play a central role in cerebral cortex networks in humans, but not in the chimpanzee, also show significant changes at the DNA level.

"When we see alterations in a gene network that correspond to functional changes in the genome, it implies that these differences are very meaningful," said Oldham. "This finding supports the theory that variations in the DNA sequence contributed to human evolution."

Relying on a new analytical approach developed by corresponding author Steve Horvath, UCLA associate professor of human genetics and biostatistics, the UCLA team used data from DNA microarrays - vast collections of tiny DNA spots -- to map the activity of virtually every gene in the genome simultaneously. By comparing gene activity in different areas of the brain, the team identified gene networks that correlated to specific brain regions. Then they compared the strength of these correlations between humans and chimps.

Many of the human-specific gene networks identified by the scientists related to learning, brain cell activity and energy metabolism.

"If you view the brain as the body's engine, our findings suggest that the human brain fires like a 12-cylinder engine, while the chimp brain works more like a 6-cylinder engine," explained Geschwind. "It's possible that our genes adapted to allow our brains to increase in size, operate at different speeds, metabolize energy faster and enhance connections between brain cells across different brain regions."

Future UCLA studies will focus on linking the expression of evolutionary genes to specific regions of the brain, such as those that regulate language, speech and other uniquely human abilities.

COMMENTARY:

Sounds to me like the differences are probably the result of different patterns of gene regulation in humans and chimps, rather than entirely different coding regions in the DNA of the two species. In other words, we share a common set of genes for making our brains, but those genes are regulated differently in the two species. This would explain a lot: why, for example, there is so little difference between human and chimp DNA, and how the two species could have diverged so quickly from a common ancestor six million years ago (or less, as some of the archaeological data seem to indicate).

It will be very interesting to see how this story develops, as we get higher and higher resolution "maps" of human and chimp brains and the genetic mechanisms that produce them.

--Allen