This is topic I wonder in forum Books, Films, Food and Culture at Hatrack River Forum.


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Posted by King of Men (Member # 6684) on :
 
if there exists any part of the human species that has been isolated long enough for genetic drift to make them nonfertile with a different part? For example, are tribesmen in the Amazon still able to have children with, say, Icelanders? Or Hausa? Has anyone checked?

/random wonderings
 
Posted by katharina (Member # 827) on :
 
Wouldn't completely non-fertile mean they were no longer the same species?

Having said that, I wonder if it is easier to get pregnant from a man who is from a similar background than from someone who is from a very different one.

My feeling, with no research behind it, is that no, there has not been that kind of drift - it would mean there was a new species of human beings created.
 
Posted by MattP (Member # 10495) on :
 
That's an interesting question. I suspect not, but that's not based on any data.
 
Posted by Mucus (Member # 9735) on :
 
Maybe someone with knowledge of dogs (not me) could have some insight. It would seem that they have been intentionally bred to exaggerate genetic drift, so it would be interesting to see if any dogs are infertile with others.
 
Posted by King of Men (Member # 6684) on :
 
I'm fairly convinced you'd have considerable difficulty breeding a Great Dane to a chihuahua. Now, perhaps it could be done by artificial insemination, I wouldn't know. But I do think that if humans disappeared tomorrow, then these two breeds would for all practical purposes be separate species - even if they were technically interfertile, they are never voluntarily going to breed, right?

This does raise an experiment we can do. I don't think any humans have been isolated for longer than we've been breeding dogs, and human generations are longer anyway. If very different breeds are still interfertile, even if by artificial insemination, then it's a good bet that all humans are too. Not a sure bet, genetics is probabilistic, but a good one. And at least with humans there's not much question of mechanical difficulties as in the chihuahua/Great Dane example. We're quite inventive sorts; I'm sure even pygmies and Masai would find a way, if they wanted to.

I remember reading somewhere that humans are more fertile with people who are related to them, but not too closely related. The ideal, IIRC, was somewhere around a second or third cousin. Take that with a grain of salt, though, my memory is fallible.

I think all humans are closely enough related that such a group would be a subspecies, or something, rather than a new species. Not a biologist, though. Besides, these categories are a bit loose, anyway.
 
Posted by scholarette (Member # 11540) on :
 
KoM- I was going to post that I remembered a study saying 2nd cousins had higher fertility. So, my memory lines up with yours.
 
Posted by Noemon (Member # 1115) on :
 
We are a shockingly uniform species, genetically; there are differences among populations, of course, but I believe I've read that there is far more genetic diversity among, say, chimpanzees than there is among humans. This is attributed to our species having a near brush with extinction in the distant past, with all of us being descended from the relatively small group of survivors. My work just started blocking all but the main page of the BBC news site, so I can't follow the link to be sure, but I'm pretty sure that this article (found by googling "human genetic diversity extinction") discusses the subject.

Here is a link to the Wikipedia page on the Toba catastrophe theory, which puts forth the idea that the Toba caldera's eruption 70 to 75 thousand years ago is the catastrophe responsible for reducing humanity to between 2,000 and 20,000 people, creating the lack of biodiversity we see today.

In any case, this lack of diversity exists species-wide.

[Edit--actually, it looks like I should have read the Toba page before posting it; my memory of the theory appears to have been hazier than I thought.]
 
Posted by Noemon (Member # 1115) on :
 
I found an old New Scientist article, Apocalypse Then, that discusses the lack of diversity. From the article:

quote:
Chimps and gorillas had roughly equal levels of diversity. But against this genetic background, humans stood out like a sore thumb. Woodruff sums it up succinctly: "There's more diversity in one social group of 55 chimps than in the entire human population."

What this suggests is that in the 6 million years or more since we split from chimps, our lineage has, at some stage, walked an evolutionary tightrope....

It is not possible to say exactly what the bottleneck would have looked like. Chris Wills, another member of the team, points out that the genetic effect will be the same with a severe bottleneck that lasts only a generation, and a less severe one that lasts many generations. "Our lineage may have been reduced by disease, chance and intergroup fighting to perhaps 20 bands of fewer than 50 individuals each, in Africa, somewhere between 500 000 and 800 000 years ago," says Woodruff. "But it is equally possible that our forebears were decimated by an epidemic and our population suddenly collapsed to a couple of bands, robbing us of our historical genetic diversity."


 
Posted by pooka (Member # 5003) on :
 
I think a scientist who studied the yanomamo of the amazon jungle was given a wife by them. He didn't think it through and left her behind when he came home, and she was treated atrociously in his absences, so he brought her back the next time and I think they had a baby. I don't think you get much more isolated than the yanomamo. The indigenous Australians also didn't seem to have any problems conceiving by Europeans.

P.S. wiki's article on pygmies is quite interesting in this regard.
 
Posted by King of Men (Member # 6684) on :
 
Ah so. You're right, as far as isolation goes, the yanomamo are pretty much it. Of course, fertility is not binary. Having established that children are still possible, it would be interesting to know if interfertility is reduced. Of course this doesn't much matter for humans, with our strategy of a few high-quality (in most cases) children. If a given couple needs to have sex 20 times instead of 5 in order to conceive, who will be complaining? A similar loss of fertility would be deadly for rats, though.
 
Posted by Starsnuffer (Member # 8116) on :
 
Even if distant populations of humans could not interbreed they would probably not be considered a different species because some intermediate of the two extremes (say a Scandinavian and an African isolated tribes) could each breed with some intermediate type of human, a Mediterranean person, perhaps. This might qualify as a subspecies, but I'm not sure.
I know this same situation IS true with some salamander species in south america, the southern variety can't mate with the northern variety, but they can both mate with the middle-of-the-continent variety, and so are part of the same species.
 
Posted by Sterling (Member # 8096) on :
 
quote:
Originally posted by King of Men:
I'm fairly convinced you'd have considerable difficulty breeding a Great Dane to a chihuahua. Now, perhaps it could be done by artificial insemination, I wouldn't know. But I do think that if humans disappeared tomorrow, then these two breeds would for all practical purposes be separate species - even if they were technically interfertile, they are never voluntarily going to breed, right?

Not without Red Bull, anyway. If the commercials are to be believed.

I feel I don't know enough about the specifics of interspecies fertility (what makes x work, y fail, z produce offspring that are themselves infertile, like mules) to speculate very usefully; I suppose the companion question would be would it be possible to engineer a species that was recongizably human and could breed with itself, yet not with the "mother" species.
 
Posted by 0Megabyte (Member # 8624) on :
 
Going back to the whole lack of genetic diversity thing...

wouldn't that be just the sort of thing that would occur if, say, the survivors of Galactica and the RTF managed to find Earth? (after being further reduced by the Cylons, of course!)
 
Posted by fugu13 (Member # 2859) on :
 
Talk about parallel threads, I recently posted elsewhere something that it is important to keep in mind:

Species is a human construct. It does not directly reflect some biological reality. It is a way of organizing how we think about and providing useful terminology for certain classes of similarities and differences between populations.

Now, many biological differences are subsumed into the idea of a species; for some random pair of species, they're clearly biologically very different. Looking at the edge cases, though, reveals lots of fuzziness, for a wide variety of reasons. At some point, individuals are members of separate species because we say they are, not because there's an objective formula that can be applied to their biological properties to determine if they're in the same species.
 
Posted by scholarette (Member # 11540) on :
 
I work with microbes (so, viruses and bacteria) and frankly, the whole concept of species is very diffiuclt for me. Defining things based on breeding compatibility when you have asexual reproduction just doesn't work. [Smile]
 
Posted by King of Men (Member # 6684) on :
 
quote:
Originally posted by Sterling:
[QUOTE]Originally posted by King of Men:
I suppose the companion question would be would it be possible to engineer a species that was recongizably human and could breed with itself, yet not with the "mother" species.

I think you could do that quite easily simply by rearranging the same genes on a different number of chromosomes.
 
Posted by Reshpeckobiggle (Member # 8947) on :
 
It's like watching Flatlanders with Ph.Ds having a discussion.

[/trolling]
 
Posted by King of Men (Member # 6684) on :
 
Well, I just proposed an experiment. Since you apparently think the said experiment would not produce the results I expect, why don't you go off and rearrange your own genes onto 20 chromosomes? Come back in twenty years and tell me if you have any children.
 
Posted by Sterling (Member # 8096) on :
 
quote:
Originally posted by King of Men:
I think you could do that quite easily simply by rearranging the same genes on a different number of chromosomes.

I'm honestly not sure. I note, for example (according to Wikipedia), that donkeys have 62 chromosomes, and horses 64.

I do suspect that if such a pair could breed, the results of such an abridged genetic code wouldn't be pretty, if it could survive at all.
 
Posted by King of Men (Member # 6684) on :
 
Well, that presumably tells us that two of the horse chromosomes can be made to match one of the donkey chromosomes. That would be because the order of the genes is the same, just with an extra chromosome break. If you seriously rearranged the genes within the chromosomes, nothing would match and breeding would no longer work. In fact, you might not even need to change the actual number. That's just insurance.
 
Posted by camus (Member # 8052) on :
 
Heh, I just read this article during lunch about early humans' brush with extinction, and then I come here and find this thread.

From the article:

"Human beings may have had a brush with extinction 70,000 years ago, an extensive genetic study suggests.

The human population at that time was reduced to small isolated groups in Africa, apparently because of drought, according to an analysis released Thursday.
...
Eastern Africa experienced a series of severe droughts between 135,000 and 90,000 years ago and the researchers said this climatological shift may have contributed to the population changes, dividing into small, isolated groups which developed independently.

Paleontologist Meave Leakey, a Genographic adviser, commented: "Who would have thought that as recently as 70,000 years ago, extremes of climate had reduced our population to such small numbers that we were on the very edge of extinction." "



Sounds to me like this might be just mere speculation that these droughts were the cause of the near extinction, but it is a new idea I hadn't heard of before.
 
Posted by Qaz (Member # 10298) on :
 
Occasionally I read an article about human genetic differences, and it always emphasizes how close we all are. If there's a group somewhere that's been isolated so long they'd have had time to become genetically incompatible...they'd have to be pretty isolated. New Guinea's highlands wouldn't do it, nor the Sahara, nor the Amazon. I just don't think it's possible. People interbreed, and migrate, too much.
 


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