The attainment of such advanced cognitive abilities would be important in order to be able to detect so-called cheaters in social exchanges. This idea is upheld by those authorities who believe in the theory of reciprocal altruism.
The selection for greater intelligence involves attaining
a bigger brain size. This required several anatomical changes for
the lineage as well. A larger birth canal was needed in the female
pelvis. A longer time interval between an individualís birth and
the time at which he or she reached sexual maturity was also needed.
This extended time period allowed for prolonged growth, learning and dependence
on parents. It is believed by some that the prolonged juvenile stage
in human development is responsible for such human features as skull shape
and sparse body hair.