Twin studies show a significant genetic contribution to altruistic traits and molecular genetic studies show that dopamine genes are involved. The stimulation of the dopamine reward pathways may make doing altruistic acts a pleasure.
These factors combine to account for the presence of altruism and cooperation at levels of magnitude that are much greater for humans than for any other species. The major lesson is that man has evolved a set of biological and genetic systems that usually lead him to behave in a helpful, cooperative and altruistic fashion toward his fellow man, independent of religion. [p472]
