Genetics determine phenotypes. Simple as that. Various groups of human populations will have varying sorts of phenotypes, depending on the original conditions

Genetics determine phenotypes. Simple as that. Various groups of human populations will have varying sorts of phenotypes, depending on the original conditions of their population. The 'long Japanese colon' may be related to the fact that Japanese are also better at digesting seaweed than other populations: http://www.wired.com/2010/04/sushi-guts/ http://www.wired.com/2010/04/sushi-guts/