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We often associate Africa as the geographical location of the origin of humans. Why cannot there exist multiple geographic locations of origin (given same environmental conditions)?

The same argument exists for other species as well. So what is the basis of the common ancestor (from single geographical location) theory?

Please give me references so that I can read more on this subject.

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    $\begingroup$ Partly depends on the resolution at which you look (both spatially and temporally) but the further you zoom in the harder it becomes to define where one species becomes two because its a gradual process which takes place over time and space. It's relatively easy to show that humans originate from Africa, harder to show that humans originate from east Africa ~400,000 years ago, and harder to show that humans originated 378,058 years ago in northern Kenya. One part of the problem is pinpointing when homo erectus (?) became homo sapiens which depends on the definition of a species... $\endgroup$ – rg255 May 26 '15 at 7:30
  • $\begingroup$ @rg255 Why cannot there be multiple sources of origin say for at Australia and Africa? $\endgroup$ – dexterdev May 26 '15 at 8:06
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    $\begingroup$ There is no reason why it cannot be. Just that the likelihood (of two exactly similar events happening at the same time) is less. $\endgroup$ – WYSIWYG May 26 '15 at 8:16
  • $\begingroup$ To me, it is unclear what you are asking. Are you asking if two different taxa can give rise to the same species at two different locations (i.e. A -> C and B -> C, if they all would all co-occur you would have A, B & C)? If so, how do you view the relationship between A & B - can they be sister taxa? $\endgroup$ – fileunderwater May 26 '15 at 10:08
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    $\begingroup$ Why is this question voted for closure because it is unclear? It sounds OK. Also because of the hypothesis that Neanderthal and hominids may have successfully interbred. Both were deemed unrelated. Although it's not my expertise and although i cannot answer this question, i feel it is a good question. Vote to leave open here. $\endgroup$ – AliceD♦ May 26 '15 at 11:20
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This is a very fundamental, and in my opinion, interesting question. You might not find many sources that directly cover this question because it is hard to test. If speciation did happen in two separate locations and the resulting species were so similar that they could breed with one another and not the original species, how would we be able to tell if the species originated in separate locations and that the new species didn't just travel to the new location? Below I'll try and explain why it's safe to assume they probably didn't have different locations for speciation.

Thought Experiment

Here is what happened in hypothetical land. Species X exists in happy land. Individuals of X then move to water land. Some more individuals from X move from happy land to H2O land (very similar to water land). Species X undergoes speciation in water land to species Y and speciation of X also occur in the H2O land to species Z.

Can Z and Y be the same species with different origins where the niche conditions are the same?

As you can imagine, the longer after geographical isolation the more mutations occur and the less likely it is that the new species will be able to breed successfully with similar species.

Although the two environments may seem identical, ecology is notoriously complex and chaotic, and so in reality as far as ecology is concerned, they are very different environments. Even the slightest difference between niches will naturally select different traits that could make Z and Y sexually incompatible.

Furthermore, when dealing with the geographical origin, you must assume that there was geographical isolation between the two speciation event locations. Since there is typically no contact between Z and Y species, there is no selective pressure to remain genetically compatible and given enough time, they will become unable to breed.

Humans

There is a contentious claim that ancient humans bred with chimpanzees after both speciation events from our common ancestor to humans and chimpanzees. Broadly I think this has now been dismissed. However, it is reasonably well accepted that in a more recent "Tolkien-esque" world humans bred with Neanderthals.

But ultimately I don't think there is a single example (I am thoroughly open to being proven wrong!) in the natural world of two similar geographical isolation events driving exactly the same species to evolve and both versions of the new species are more genetically similar to one another than they are to the origin species. The odds are just too slim even if to us the conditions seem identical.

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References - Wiki article about the theory of multiregional origin for humans. The wiki article clearly states up front that this is "an alternative explanation to the more widely accepted Out of Africa model". One issue brought up in this article, is although there doesn't seem to be any unique localized single feature, there has been unique combinations of localized features found in early fossils in locations like Australia. The wiki article includes further references.

http://en.wikipedia.org/wiki/Multiregional_origin_of_modern_humans

The more accepted theory is "Out of Africa". Wiki articles:

http://en.wikipedia.org/wiki/Out_of_Africa_I

http://en.wikipedia.org/wiki/Recent_African_origin_of_modern_humans

http://en.wikipedia.org/wiki/Early_human_migrations

Another article that explains why "Out of Africa" is the more accepted theory:

http://www.actionbioscience.org/evolution/johanson.html

Note that all of this is with respect to modern humans. I don't know if there are any animals or plants where multiple source for the same species is the more accepted theory.

Hybrids (the offspring of two compatible, but different species parents) could occur if the parents where multi-regional. You can do a web search for polyploid hybrids and tree frog for examples of this, but these are hybrids, not mutations.

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  • $\begingroup$ Citing wikipedia alone is risky, as its contents are dynamic and often based on questionable sources $\endgroup$ – AliceD♦ Nov 18 '15 at 1:29
  • $\begingroup$ @AliceD - The OP asked for references. The wiki article clearly states up front that this is "an alternative explanation to the more widely accepted Out of Africa model", and the wiki article contains links to references (again, what the OP was asking for). I updated my answer to make this more clear. $\endgroup$ – rcgldr Nov 18 '15 at 5:29
  • $\begingroup$ Those references may be disputed or deleted altogether over time. Cite the primary references if they are good. $\endgroup$ – AliceD♦ Nov 18 '15 at 5:44
  • $\begingroup$ @AliceD - the wiki article was originally created July 2014, and has been continually updated since by multiple people. The references have been there during much of this time, and should have been deleted by now if that was an issue. I would assume that less accepted already means it's disputed, and the wiki article covers this. The talk page should include discussions about the article or disputed references. I'm not a proponent of this theory, and only posted the link since the OP asked for references. $\endgroup$ – rcgldr Nov 18 '15 at 6:19
  • $\begingroup$ All good. I'm just explaining my downvote. I'm not saying wiki is per definition not OK, I'm saying I am not a fan of wiki-only answers. That's all. You might get a bunch of upvotes from others. Because of your research into the wiki page I'll remove the -1 :) $\endgroup$ – AliceD♦ Nov 18 '15 at 7:48

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