Wednesday, December 2, 2015

Chimpanzees in the Stone Age

What makes humans special in the animal kingdom? Decades ago, one of the answers to this question was tools. Humans were unique, many thought, in their genetic heritage of conceiving and constructing useful items from natural materials. Then, in 1960, Jane Goodall witnessed chimpanzees using stripping grass stalks and using them to fish for termites. Her mentor, Louis Leakey, said this:

“Now we must redefine ‘tool’, redefine ‘man’, or accept chimpanzees as humans.”

Since then, we have learned a lot about tool use in the animal kingdom; dolphins use sponges to stir up sand, elephants scratch themselves with branches, crows hold twigs in their beaks to probe for insects, and primates have been recorded selecting or modifying items in their environment to serve as sponges, pillows, spears, hammers, and even possibly medicine.

Nut cracking is an especially well-documented illustration of the observational learning, forethought, and problem-solving required by tool use. As shown in the second video, some nut cracking sites have been in use for so many generations, pits have been worn into the anvil stones. Obviously, this is a behavior that monkeys and apes have been at for a long time.

A 2007 discovery in Côte d’Ivoire, Africa, offers hints about just how long that might be. A team of 'primate archaeologists' led by Christophe Boesch excavated a section of rainforest known to have been occupied by chimpanzees for a long time. They discovered tools- heavy stones bearing traces of starch- more than 4,000 years old. The hammer stones are heavy, much heavier than a stone a human would choose, which is unsurprisingly considering chimpanzees' amazing upper body strength. The starch residue, a product of cracking countless tough husks, comes from a nut that chimpanzees eat but humans don't. This evidence indicates that chimpanzees have been using stone tools for since at least 2000 BC-- around when humans began making paved roads-- and possibly much longer than that.

The idea that other animals make and use tools is still relatively new, and newer still is the idea that they may have their own archaeological sites worth looking for. These hidden sites could have much to teach about the evolution of intelligence in our family tree.