Their reason given is colder climate zones are more cognitively demanding, as more measures had to be done to survive Such as cloth, shelter and lower temperatures etc. This eventually coursed natural selection for higher cognitive ability thereby bigger brains in colder climates.
Their reason given is colder climate zones are more cognitively demanding, as more measures had to be done to survive. This includes cloth, tools, shelter and fire in order to survive lower temperatures, less plant food to eat, seasons etc. which coursed natural selection for higher cognitive ability thereby bigger brains in colder climates.