All human nature can be traced back to evolutionary necessity. At one point in human history resources were scarce. We were hunter-gatherers and our tools weren't very sophisticated. Thus humans (and most animals) have an instinctive drive to seek out and acquire more and more resources for survival.
Even when times are good (say, we have plenty to eat), our biological tendencies tell us to "get while the getting's good" and keep eating so that when the inevitable scarcity comes we will have enough fat stored to get through it. It's why obesity is an epidemic and why it's so hard to get over cravings.