Which of the following observed chimpanzee behaviors caused scientists to reevaluate what it meant to be human?

a. kissing

b. holding hands

c. tool making

d. speaking

It was the tool making!

Before discovering that chimpanzees can make tools, people believed that tool making is specific to humans and that it defined being human.

After this discovery, people had to re-think what it means to be human: either chimpanzees are humans too, or took making is not unique to humans