Why are we so genetically similar

[Monique]

Culture Shock May Explain Similarity Between Humans

"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."
http://sciencenow.sciencemag.org/cgi/content/full/2009/108/2?etoc

[marcus]

... 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."
http://sciencenow.sciencemag.org/cgi/content/full/2009/108/2?etoc

Correct me if I'm misunderstanding, Monique, but the scenario here seems not TOO different from the old bottleneck idea.

Bottleneck said that at one time the group of ancestors was reduced down to about 10,000 breeding adults---for whatever reason.

New scenario says essentially the same thing: the genepool was balkanized by ethnicity (antipathy to people with different language, ceremonies, tools, music, clothing, whatever). Preference for one's own culture caused a lot of inbreeding within each of many many cultural groups.

Maybe a typical size for a culture group was 10,000----just say.

And then (most or) all but one of the culture groups went extinct! Sounds like a genetic bottleneck.

==quote==
Genetic variability plunged when individuals required mates with the highest degree of cultural similarity, the team reports this week in The Proceedings of the National Academy of Sciences. Conversely, genetic diversity increased when individuals were less selective about their mates--as is the case in chimpanzees or gorillas, which mate whenever possible with individuals from other groups.

Hublin and Premo propose that if human ancestors selected mates from similar backgrounds, there would have been a lot of inbreeding within different populations, restricting the flow of new mutations to other groups. "If these guys on the other side of the river spoke a different language and had different weapons, you would not try to mate with them or they might kill you," says Hublin. Over time, most populations went extinct, allowing the genes of only a few groups to proliferate, further erasing genetic diversity.
==endquote==

Dear Monique, if I could summarize, what it sounds to me like is just another bottleneck theory but the bottleneck, instead of being caused by volcanic eruptions or climate change or something, the bottleneck is caused by the vulnerability of early humans to
xenophobia-based inbreeding.

And without some more discussion of what might have caused almost all the inbreeding culture groups to go extinct (since Polynesians stuck on islands don't go extinct automatically) I find the scenario interesting and worth considering but not fully convincing.

[TheStatutoryApe]

Isn't interbreeding between primate species somewhat common?

http://www.sociologyanthropology.ilstu.edu/downloads/anthro_theses/lass_beth.pdf
Ah... here's an interesting paper on the subject I just found. I can't read it all right now but it apparently discusses the phenomenon of interspecies breeding among primates and its effects on genetics among other things.

So this could account, perhaps to some degree, for the greater genetic variation in other primate species aside from humans.

[Potential]

Culture Shock May Explain Similarity Between Humans

"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."
http://sciencenow.sciencemag.org/cgi/content/full/2009/108/2?etoc

The less diverse genetic material of humans relative to chimps and or gorrillas could have to do with a hypothesis of humans almost becoming extinct at one time relative to the other species. How does polar bear genetic diversity compare with humans?

[mgb_phys]

The less diverse genetic material of humans relative to chimps and or gorrillas could have to do with a hypothesis of humans almost becoming extinct at one time relative to the other species.
Yes that's the bottleneck theory, it estimates that H. Sap was reduced to somewhere between 1000-10,000 pairs at some point around 50-100,000 years ago. It's worse for cheetahs - they were reduced to possibly <100 at some point.

The balkanisation theory would suggest more genetic diversity rather than less I would have thought - wouldn't you get a ring species where tribe A would marry tribe B but not C, while B would marry C but not D - until you get to Z which cannot breed with A?

Doesn't the cultural theory explain why different races look different? So Japanese have no local genetic advantage to being Japanese shaped but culturally anybody not Japanese shaped didn't get laid? That is the normal explanation why people who don't need extreme body types for the local environment (eg Eskimos or bushmen) still evolve a distinct race.

[Potential]

Interesting. Another possible way for low human genetic diversity relatively speaking, would be the hypothesis of a huge world war where most of the males, if males were the ones sent to battle, were terminated. In this case, the remaining male genetic material would be more concentrated.