Researchers from Oxford University have found that there is a direct correlation between latitude and brain size. People in northern countries have bigger skulls and bigger brains than those in southern countries. This doesn't mean that they are smarter, but rather, that they need bigger vision areas in the brain to deal with the dimmer lighting. The correlation is very specific — in the Oxford study, which included 55 skulls, each skull could be matched to the latitude of the country where the owner lived by its size alone.
More facts about brain size:
It makes sense that the species that consciously uses the least of its brain in relation to its size
would consider itself the smartest. Kimberley W., montreal 2011