Answer:
Correct answer is They were searching for recourse necessary to live.
Step-by-step explanation:
First option is wrong as early humans weren't that curious to research and exploit lands, as their routine was based on surviving.
Second option is wrong, as they weren't farmers, but hunters and food gatherers.
Third option is correct as they would move to find a place where they could hunt, gather food and find a shelter.
Fourth option is wrong because there was no overpopulation. Actually, most of the Earth was inhabited.