Human motivation resides in the brain, which has been evolving for millions of years. Its proximate purpose in every generation was to guide its bearer to take the actions that would best promote the transmission of its genetic blueprint into the next generation. The Darwinian framework is the only scientific framework available for trying to understand why humans and other animals are motivated to behave as they do.

Frank, Robert H. (2011-09-05). The Darwin Economy: Liberty, Competition, and the Common Good (p. 24). Princeton University Press. Kindle Edition.