Natural selection is not considered a sufficient explanation for the tripling of human brain size in the past two million years. The human brain started a growth while other closely related hominids in the same habitat remained at their current level. Human brain growth stopped about 100,000 years ago, long before the Neolithic revolution in technology and art 40,000 years ago. At least two theories have arisen to explain this trend. In the runaway social competition model, rapid encephalization occurred so hominids could predict and manipulate each other's behavior, leading to a social intelligence arms race between mind reading and deception.
Sexual selection is the clearest and best established case of positive feedback evolution in nature.
Runaway sexual selection on production and discrimination of viability indicators could be responsible for our current level of intelligence. Before the development of the entertainment industry, we had to provide our own amusement. Sexual competition has generally been overlooked as an explanatory principle. Sexual selection theory has provided the only coherent, non-circular account of gender roles in culture. It gives a parsimonious explanation for gender-based cultural dimorphism, that most economic behavior is mating effort by males to acquire material resources for attracting and provisioning females.