Several researchers - notably Katherine Milton (University of California at Berkeley) and Katherine Gibson (University of Texas) - have attributed the enhanced cognitive capabilities of primates to the rigors of foraging. Milton describes how the formation of a detailed spatiotemporal cognitive map could assist foraging among frugivorous primates, particularly since (1) their food type is likely widely distributed, and (2) resource abundance is seasonal in nature. They literally could remember where they were, and return successfully. Selection for memory and efficient foraging techniques would definitely have proved to be an advantageous attribute.

Another foraging hypothesis - suggested by Katherine Gibson - states that the extraction of embedded resources provided the impetus for the evolution of primate intelligence. Extractive resources - foods which are hidden from sight and often difficult and time-consuming to exploit (e.g. roots and underground tubers) - usually require delicate manipulation and processing to recover successfully. Additionally, many of these resources provide essential nutrients during the dry season. The ability to augment dietary intake with nutritious, hard-to-reach resources may also have played a part in the increasing cognitive capacity of the primate order.

Social Intelligence Hypotheses

An alternative view considers group living to be the primary force behind the evolution of behavioral complexity and intelligence. One of the proponents of this idea - Robin Dunbar (University of Liverpool) - considers the relationship between group size and relative size of the neocortex of the brain, under the assumption that neocortical increases should be observed in groups with more members. More members suggests increasing complexity of social dynamics; this also means more individuals (and their past actions) to remember, and more competition for resources. This model also has support in empirical evidence which correlates relative neocortical size with group size, whereas the two ecological models do not exhibit any correlation between relative size of the neocortex and foraging strategy.

The idea that social manipulation, or Machiavellian intelligence has been instrumental to the development of cognitive complexity is a theory proposed by Andrew Whiten and Richard Byrne, both from the University of St. Andrews (Scotland). Deception and alliance formation are but two of a vast array of techniques utilized by members of the primate order to manipulate other individuals in their social group. Additionally, the core concept behind social manipulation and the initial definition of intelligence - flexible problem-solving behavior in novel situations - may be very similar: both require a conscious manipulation of elements, as well as a rudimentary knowledge of the relationship between different elements.