The savage origins of the species and the development of capitalism.
In order to expand and clarify my previous comment:
I suggested that capitalism is a manifestation of the evolutionary history of the species. However, capitalism is not as old as the species. For the most part, it dates to the 16th century. My contention is that the complex of behaviors that proved adaptive to the environment that existed in Pliocene times, when expressed through the environment that has existed since the 16th century, manifests itself as capitalism.
The Pliocene environment (and other early human environments) was harsh, the human population was small and scattered, and the developments which enable cooperation on a large scale did not yet exist, therefore, in order to survive, humans were necessarily predatory and acquisitive. In such an environment as they lived, such behavior was not harmful and was, in fact, successful for the species as a whole. However, as the population increased, became less scattered, and developed means of large scale cooperation, these bahaviors became less adaptive to the environment. With the late middle ages came greater populations, greater concentrations of population, and greater means of coordinating the activities of these populations. Human behavior did not evolve as fast as the environment changed, and capitalism is the result of these primitive behaviors expressed through modern environments.
The aggressiveness of the hominid was necessary to its survival. It needed this characteristic in order to defend its kills from other predators and scavengers. However, when this aggressiveness is expressed through modern technology, it is manifested as the mechanized butchery of the twentieth century. Likewise, the selfishness and acquisitiveness of the isolated bands of hominids worked well in their environment, but when expressed in a modern environment it becomes just as destructive as the aggressiveness.
Moreover, capitalism has made the modern environment nearly as hostile and uncertain to the average human as it was at the beginning of the species. This is the simple result of wealthy humans using the power of their wealth to reshape the environment into one which is maximally amiable to them and their objectives. Now, once again, ruthless predatory behavior is necessary to prosper. In essence, thousands of years of evolution have failed, and we appear to be sliding back into the brute slime from which we came.