Decades ago, it was commonly believed that humans were the only animals that used tools. We now know that this ability is surprisingly common: elephants and crows use tools, as do some fish. And of course, primates do too—though until recently the only tools scientists had witnessed them using were plant-based, like twigs and sticks.
In the early 2000s, so-called "primate archaologists" published a landmark study that described a 4,300-year-old site rich in stone tools—stone tools the researchers were sure didn't come from humans. That could mean chimpanzees are currently living in their own Stone Age, and it could pre-date the arrival of human farming villages in the same region of the site.