Over the course of millions of years, primates’ evolutionary ancestors developed their brains to the point that the brain became the most energy intensive organ in the body. Large brains are very costly investments for an organism, both in terms of percentage of energy consumption, and in terms of the period spent outside the womb in which the organism is unable to defend itself (Cheney & Seyfarth, 2007). Based on evolution scientists know this fact to be true. The only question remaining is: what in the many varied environments of primates led to this overall increase in relative brain and skull sizes?
Many scientists argue that only either social or ecological pressures that the worldwide primate population faces led to the eventual development of larger brains and increase cognitive ability. It is also a very widely held scientific belief that neither of these environmental pressure-types was solely responsible, but in fact that some distinct combination thereof resulted in the anthropologically documented increase in average relative primate brain size (Cheney & Seyfarth, 2007). If a combination of these two pressures was responsible, then necessarily either social or ecological intelligence must have come first and subsequently led to the proliferation of the other.
Realistically, the most likely scenario is that early primates first gained the vestiges of intelligence from ecological factors which were necessary to maintain even the most basic levels of survival, and then, once they began to gain certain evolutionary advantages from that intelligence, they expanded and fine-tuned it by means of social interactions and communication. This explanation gains an exceptional amount of credence from the fact that in order for an animal to reproduce and succeed in evolution at all, it must first provide itself food in some fashion and survive amidst various predators. Only once an organism has already attained a certain level of sustained basic survival in the world can it begin to flourish and excel in the nuances of its own ecosystem and environment, by adding the comparatively marginal benefits of social groups and societies. If social intelligence arose first, it would almost definitely necessitate circumstances in which many of the social benefits of reproduction were more influential on survival than food. In other words, an environment so completely saturated by food and with such a limited number of natural predators, that the need for ecological intelligence was almost completely eliminated, and that primates would be likely to stumble on to food with only minimal effort or intent.
While there is a wealth of information in favor of each of these two hypotheses, it is unlikely that one or the other is solely responsible for the development of primate intelligence. This is largely because social and ecological factors are inextricably linked in many aspects of the lives of primates because most primates live in some sort of social...