Hunters have distinctly different requirements to farmers. A hunter needs to be continually aware of his surroundings, so his attention will quickly focus on anything that may be a threat or opportunity. As a hunter, novelty, constantly monitoring the surroundings, and creativity are the most important requirements for success. He needs to be able to sustain a steady, even level of effort, even with no apparent clear gain in the immediate future. Our brains learned to cope with life as a farmer by producing more dopamine.
Some theories suggest that dopeamine developed as a survival technique for seige like situations.
If a monkey is sitting in a tree with a lion prowling around below then being patience is essential for survival. Dopamine calms down the monkey and allows him to out-wait the lion. In todays society we spend a lot of time in waiting situations. In fact, it would be more accurate to say that we spend almost all our time in waiting situations. Our dopamine levels are much higher than nature intended.