What does cross-cultural research suggest in relation to the "incest taboo"?

Sociology is best described as the systematic study of

The controlled use of fire by hominids: (a) limited the expansion of hominids into certain environments, such as dry grasslands. (b) decreased the amount of food energy available in the hominid diet. (c) contributed to geographical expansion and food production techniques in positive ways. (d) has been shown to contribute little to the digestive process of hominids.

On average, being married has a(n) effect on happiness.