They were trying to figure out how to survive in a harsh world filled with deadly predators -- without the benefit of sharp claws, poisonous fangs, heavy muscle

They were trying to figure out how to survive in a harsh world filled with deadly predators -- without the benefit of sharp claws, poisonous fangs, heavy muscles, thick fur, or any other advantage normally afforded to their competitors. That meant learning, for example, how wind and gravity affect the trajectory of a spear through the air. It's not rocket science but it's close enough :p Since we're here, it seems that they succeeded!