More than 40 years ago, a Colombian sociologist explained why inside the cranium groups can differ significantly. It originates in how one acquires food in harsh climates. In what is now the tropics one pulls a fish out of the river or a mango from the tree year-round. There is no survival advantage conferred by advance planning. In the northern climes this is not true. If one does not lay away fish, meat, dried vegetables in the fall (advance planning), one does not survive until spring.

Any gene or group of genes that promotes advance planning is largely a waste in the tropics.