When a joint research team from Iowa State University and the University of Cambridge studied chimps in the wild, what they saw was a fairly methodical, step-by-step process of fashioning what most of us would recognize as a spear. The chimps would first break off a live tree branch, usually about 2 feet (0.6 meters) long; then pull off any leaves and twigs; then, in many cases, scrape off some of the bark at one end of the stick and create a point at that end of the stick by gnawing away at the tip with their incisors.
The sharp-point part is a big deal, because no one has seen a chimp sharpen a stick in order to use it to enlarge a hole in a log. This element supports the case that the chimps are creating a spear.
The chimps would then jab the stick into a hollow tree branch or a hole in a tree trunk, which are places where a lemur-related animal called a bushbaby (Galago senegalensis) sleeps during the day. The jabbing was in the motion humans typically think of as "spearing." Of 22 observed cases of this type of action, Pruetz and Bertolani saw only one in which the spear actually pulled a bushbaby out of a tree. But in some cases, the chimps would jab wildly with the stick and then pry open the hole from a bit of a distance in order to get to the bushbaby. Pruetz explains that this seems to indicate the chimps are in fact trying to kill or immobilize the animal with their jabbing, because bushbabies are quick -- if the animal were unharmed when the chimp pried open the hole, it would easily scurry away and evade capture. Also, the chimps would usually sniff or lick the spear after pulling it out of the hole, and the researchers found discarded spears with bushbaby fur stuck to them.
There is a common belief in the scientific community that females played a key role the evolution of human tool use. As observed in the chimpanzee community, the adult males are typically the last to pick up a new method of accomplishing a task. The adolescent males and females seem to be far more open to adaptation. And since adolescents spend most of their time with the females of the community, biologists have theorized that females are the primary innovators in tool use. The females use tools to adapt to changing conditions and pass along the adaptations to the young of the group, who easily pick up the new tool use. The adolescents eventually become the alpha males and the offspring-rearing females, solidifying the new tool in the daily life of the group. With 96 percent of human DNA matching chimpanzee DNA, the latest observations of female-dominant tool innovation in a chimpanzee community could provide fuel for the theory of female-driven tool innovation in human evolution.
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