I would appreciate some hypotheses.
Here is a map of the world by IQ:
http://upload.wikimedia.org/wikipedia/commons/7/7e/IQ_by_Country.png
It seems that generally the further away you are from the equator, the smarter you are. My hypothesis is:
1. You need a high IQ to survive colder areas. You need to be able to foresee the future and plan for the winter. People with low IQs are not good at planning for the future. Surviving the winter, growing food and getting water in the winter forces you to work hard which stimulates brain activity allowing most to achieve a higher IQ.
What do you think?