Abstract: Since biology is the study of living organisms, their behaviour and social systems, and since humans are living organisms, it is possible to suggest that social sciences (the study of human behaviour and social systems) are branches of biology and all social scientific theories should be consistent with known biological principles. To claim otherwise and to establish a separate science only for humans might be analogous to the establishment of hydrogenology, the study of hydrogen separate from and inconsistent with the rest of physics. Evolutionary psychology is the application of evolutionary biology to humans, and provides the most general (panspecific) explanations of human behaviour, cognitions, emotions and human social systems. Evolutionary psychology's recognition that humans are animals can explain some otherwise perplexing empirical puzzles in social sciences, such as why there is a wage penalty for motherhood but a wage reward for fatherhood, and why boys produce a greater wage reward for fathers than do girls. The General Social Survey data illustrate the evolutionary psychological argument that reproductive success is important for both men's and women's happiness, but money is only important for men's.