User blog comment:Ralok/Humans (appearence)/@comment-730941-20100429121848

I think the books explain the aliens' lack of diversity by saying that humans are the most recent species to unite globally; and the other major species (drell, turians, asari, salarians) all look so similar because they've been one society for thousands of years (and genetic diversity was reduced).

It says that humans are starting to follow suit, which is why we have David Anderson (born in London with a mixture of African, Central European and Native American heritage) as a typical example of a human.

Nice guide to humans by the way. If I didn't know what I was then it's a good start :D