Aggressive behavior in males has been linked with low levels of and high levels of testosterone.

I'm guessing estrogen, since that's a female hormone but i'm not sure.

During the paleolithic, hominins grouped together in small societies such as bands, and subsisted by gathering  plants  and fishing, hunting or scavenging wild  animals. the paleolithic is characterized by the use of knapped stone tools, although at the time humans also used  wood  and bone tools.