The discovery of a chimpanzee making and using a spear in Senegal is not only a surprising revelation about our nearest evolutionary relative, say Mairi MacLeod and Ian Sample - it could also provide invaluable insights into how man developed technology
Friday February 23, 2007
In the dry heat of the west African savanna, a chimp called Tumbo hauled herself up into a wizened tree. She had spotted something: an interesting-looking hole at a fork in the trunk. Watching her, researcher Paco Bertolani suspected that she was looking for insect larvae to eat; the chimpanzees had done this before. Tumbo grabbed a thin branch, snapped it free and purposefully honed one end, using her teeth to make a point. Then, she moved closer to the hole, grasped the primitive spear, and rammed it inside with as much might as she could muster. Afterwards, she pulled it out and sniffed and licked the end. Tumbo repeated the violent stabs again and again until, apparently satisfied, she moved across to a withered branch adjoining the trunk and leapt up and down to break it free. From within the now exposed hole, she retrieved an unmoving bushbaby, evidently dead as a result of the onslaught. She sat down and calmly dismembered the animal, chewing on the meat with relish and accompanying her meal with odd handfuls of fresh leaves.
Tumbo is the first chimpanzee to be seen making and using a tool to hunt for meat. Details of her spearing her prey are revealed for the first time today in the journal Current Biology. Such behaviour has never been seen before, and it represents an important leap forward in our understanding of just how sophisticated chimpanzees - humankind's closest relatives - really are.
There was a time when scientists believed that one of the major differences between us (humans) and them (animals) was tool use. But those days are long gone. Last year, chimps in the Congo were captured by hidden video cameras using stick tools to dig and dangle for termites. Earlier this month, a crop of ancient stone tools dating back 4,300 years were unearthed and identified as having been used by chimps, fuelling a debate about a chimpanzee Stone Age and the chance that both chimps and early humans inherited tool use from a common ancestor. Now there's Tumbo using a spear.
We have certainly come a long way since a young Jane Goodall began her inspirational research into chimpanzee behaviour at Gombe in Tanzania in the 1960s, back in the days when chimps were seen as innocent, peace-loving creatures (since then, they have been observed hunting down monkeys in coordinated groups, not to mention murdering each other). Increasingly, chimp behaviour is being found to be so human-like that it is giving scientists invaluable insights into the evolution of early humans.
"Technology is one of the most important aspects of the human condition. It's the reason we've conquered the planet, but it had to come from somewhere," says William McGrew, a primatologist and expert on the evolution of material culture at Cambridge University. "Short of inventing a time machine, the next best thing is to look at our nearest living relations and their technology." According to McGrew, evidence from the archeological record suggests that our hominid ancestors started using tools in hunting around 400,000 years ago in Europe. "And what do you think [they used]?" he asks. "Sharpened wooden sticks. It is essentially the same weapon that's being used by these apes, except it's bigger."
But why has spear-making by chimpanzees never been seen elsewhere, despite decades of research? The reason could be that chimp behaviour in this particular habitat - the hot, dry savanna of Fongoli in Senegal - has not been studied in detail before. Chimps adopt different strategies in different environments: complex cultural differences have emerged between populations. And the Fongoli chimps do seem to be quite an unusual population. As well as using spears, they have taken up residence in a number of caves, worn from rock by millennia of flowing water. It seems they like to use them for picnics and siestas, or to shelter from the heat during the day.
Bertolani, of Cambridge University, who is collecting data for his PhD, once spent the day with Fongoli chimps in one of their more open caves and witnessed events not out of place in a soap opera. He says some rested and groomed, others quarrelled, while males showed off, running in and out of the cave for the benefit of a female. Others did their best to ignore the spectacle and carried on sleeping in the dark recesses. Researchers have also witnessed the chimp equivalent of a pool party - with no little astonishment, because chimps usually have a strong aversion to water. "Chimps are reckoned to be hydrophobic, because they sink like stones," says McGrew. "Then along come the Fongoli chimps, who, when the rains come in May and fill up the depressions in the plateaus, jump in and sit there up to their chests, all crammed in together."
"They run through and splash each other and display," says Jill Pruetz, director of the Fongoli project at Iowa State University.
One of the most intriguing things about the Fongoli spear use is that it is females who do the hunting. Monkey hunts by chimps are well documented, but they are dominated by the big males. Although females occasionally take part in hunts, it's normally a back-seat role. Charging through the trees is dangerous, especially with a small infant, and even if a female catches the quarry, there's a good chance she will have to surrender it to a larger male.
Pruetz says females and youngsters are forced to innovate to get protein for their diets; her point is that it is females who are driving the adoption of new technology. "The females and maybe the young males too are basically having to solve problems in a creative way because of competition with adult males," she says. "That may be by technology, and not by brute strength or force."
"Basically, you can spot that tree hole and you can creep up and take a good look," says McGrew. "You can do that even if you're encumbered with an infant, and because it's a solitary activity, you don't have to coordinate with others."
The researchers say spear use in Fongoli is performed almost exclusively by females and youngsters. In spite of the fact that the researchers were concentrating on male behaviour during their study, they saw only one attempt at spear-making by an adult male out of a total of 22 episodes.
"[This] strengthens the case that in all likelihood the origins of technology [in humans] were with females," says McGrew.
The chimpanzees at Fongoli have been habituated to humans for less than two years. In that short time researchers have discovered a wealth of new chimpanzee behaviour. What else are these apes going to surprise us with? Pruetz says she is learning to expect the unexpected and is hoping that it will be possible to keep the research going at Fongoli far into the future. So we know now that chimps are skilled and cooperative hunters. We know they are capable of terrible violence, but also empathy and, according to some observers, even primitive morality. We see the roots of human behaviour in wild chimpanzees today: they are on a behavioural continuum with us. But how far, if anywhere, will their technology go? Humans achieved great leaps in technology only after millions of years of environmental pressure gave rise to more complex brains.
"Chimps do a pretty good job of tackling their problems without developing technology. What's instructive is when they need it," says McGrew. Chimps have the advantage of big, strong jaws and teeth, he says, so they can accomplish many of their jobs without tools. But, he says, "even after human technology took off, it took millions of years to get notable changes, so for us primatologists to be lucky enough to see anything in a couple of decades is highly unlikely. Every one of us would love to be on the scene when there's an important advance in chimp technology. It hasn't happened yet, but we live in hope."