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.

 

[ben8494]

If the bottleneck happened again say in the next 20 years and only people from Norway were alive after such a disaster would there be any advantages to everyone being similar. I understand that if everyone way very genetically similar the entire human race could die from a single deadly virus but would it not also decrease the human race's susceptibility to specif ic disease??

 

[moodalert]

Dare I say that we're not genetically alike at all. Statistically most humans are but there's a distinct percentage that differs in a profoundly major way.

 

[ben8494]

Dare I say that we're not genetically alike at all. Statistically most humans are but there's a distinct percentage that differs in a profoundly major way.

Moodalert, do you have any data to support this statement? So who exactly differs so profoundly from the mean?

 

[plus]

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

Why do you think that genetics is contributing to the differing body shapes of the two tribes and not food/ lifestyle differences?

 

[ben8494]

Why do you think that genetics is contributing to the differing body shapes of the two tribes and not food/ lifestyle differences?

Genetics are the only constant in this because if you take a Masi warrior child and put them in the artic with the same diet and lifestyle of an Inuit. The Inuit will still be better suited to the artic due to their tiny genetic differences this is how we can conclude that genetics is the contributing hactor and not environmental factors.

 

[Antiphon]

Humans are nearly identical across the globe. I believe it's because there are zero strong selections going on.

The modern diversity of dog species has been accomplished in less than two hundred years by very strong and diverse selective breeding. Since dogs reproduce at least 7 times faster than humans, an aggressive selective breeding program in humans with similar results to that of dogs would take perhaps 900 years.

But since nobody is doing it, we'll never see it happen.

 

[tjfloyd]

Yea, we are very genetically similar.. in fact, according to a documentary on the National Geographic channel, we are 99.9% genetically similar.. however, that 99.9% is the genetic information that makes us human.. what gives us a heart and brain and two legs and a symmetrical body. Now, the other 0.1% is what gives us individuality: hair color, eye color, personality, cognitive capacity, craniofacial structure, height... you get the idea.. Although 99.9% sounds like all humans are just alike, that 0.1% still contains millions of billions of different genetic combinations..

 

[ajweibel]

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.

Genetics has shown an ability to indicate geographical location of a person's ancestry. Yet, I am unaware of any study which shows there are actual human races. I can understand saying human race, meaning mankind. Yes, I understand people are different and look different. But, that does not make a race.