People are Pretty Much Alike: Researchers Have New Idea for Why

"Culture Shock May Explain Similarity Between Humans"
ScienceNOW Daily News (January 8, 2009)

"Although humans come in many shapes and sizes, from the compact Inuit of the Arctic to the willowy Masai warriors of Africa, any two people are a lot more alike genetically than any pair of chimpanzees or gorillas. The reason may be our advanced culture, according to a new study. Our ancestors' different tools, eating habits, and even body decorations limited their mate choices to individuals of a similar culture, the work suggests, reducing the spread of new mutations across many groups. Because only a few of these ancient groups survived, humans are much less genetically diverse than other primates, even though there are many more of us on the planet.

"Ever since researchers discovered in the 1970s that humans lacked the genetic variation expected of our population size...."

This idea seems to make sense - and is less unlikely than some others that explain why people are so much alike.