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I recently heard about the evolution of the London Underground mosquitoes, and how they have changed genetically enough that they almost can no longer reproduce with above ground mosquitos. Since this change in the mosquitos occurred over a relatively short time frame, how many years/generations would it take for a similar process to happen with humans?

The thought experiment that comes to mind is this. Assuming we sent a colony of humans to a distant planet and didn't have any physical contact with them for x number of years, how many years would it take for the colony of humans to branch off enough genetically to be no longer be able to reproduce with Earth humans? This is assuming the planet is habitable but different enough to change the course of human evolution.

In other words, what would be an expected minimum number of years it would take for this colony's descendants to be removed from Earth humans to one day again be reunited and not be able to produce offspring between the now different species?

In other words, what would be an expected minimum number of years the would need to pass before they are reunited and are no longer enough of the same species to produce offspring together?

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closed as primarily opinion-based by anongoodnurse, WYSIWYG, One Face, The Last Word, fileunderwater Jan 13 '15 at 10:40

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Welcome to Biology SE! Very interesting question! Although I am not an evolutionist, and I may be wrong here, but I think this question will likely yield only speculative answers. Perhaps it could be rationalized by stating the question as "how long did it take our earthly homo forebears to evolve into species that were genetically incompatible with their predecessors?" $\endgroup$ – AliceD Jan 12 '15 at 23:45
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    $\begingroup$ Chris, good point! I realize it is very theoretical, and I assume that the past evolution of our species would be a good indicator of how long this process would take. I suppose the difference here is that it would be an instant separation of the species, rather than a slow migration like our past homo forebears. And there also would be no cross-breading during this time, like it has been expected to have happened with various homo species of the past (slowing down the branching of evolution). $\endgroup$ – timgcarlson Jan 12 '15 at 23:55
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    $\begingroup$ If Australian Aborigines are any indication, it would take a long time. They arrived in Australia on the order of 50,000 years ago and were still genetically compatible with other humans when settlers arrived within the last 500 years. Prior to exploration in the last few centuries travel to and from Australia would have been pretty negligible. $\endgroup$ – user137 Jan 13 '15 at 0:21
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    $\begingroup$ @ChrisStronks about closing questions on questionable grounds. Chris and I had discussed this on chat that this is same as cleaning the lab fridge. Lots of junk is cleared but sometimes a somewhat important stuff is also gone. That is one tradeoff. We can have meta discussion on deciding whether to reopen those questions or not (as such those questions are not that common). It took quite some effort to clean up the site. $\endgroup$ – WYSIWYG Jan 13 '15 at 12:44
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    $\begingroup$ I don't get the votes to reopen, since it hasn't even been edited after it was closed (besides a retag). At least give the original poster a chance to respond to the suggestions/criticism and maybe clarify before voting to reopen. What's the hurry? $\endgroup$ – fileunderwater Jan 13 '15 at 13:42
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That's an interesting model, because mosquitoes are vectors for serious illnesses, so are pretty well studied. One team of scientists are working on genetically altering mosquitoes in Africa to make them unable to transmit the parasite that causes malaria. As the mosquitoes breed, it spreads through the population. In an interview, the lead researcher stated:

In the lab, we saw the mutation spread to more than half the population of mosquitoes we had living in cages. This happened in a time span of 12 to 16 generations of mosquitoes (each generation being between 18 to 30 days in the wild). So it's quite efficient.

12 to 16 generations for one mutation to spread to half of a contained population. In human generations, 16 = 320 years, and that doesn't take into account fertility rates, miscarriages, etc. (Not a problem for mosquitoes, I presume).

How many mutations would it take to make two humans incapable of reproducing without endangering their own health or fertility? Excluding all of the harmful mutations that might just result in disease or decreased fertility? And add to that that the males need to change as well as the females? No one knows.

Imagine a cystic-fibrosis type mutation (one gene) that increased the viscosity of cervical mucus such that normal sperm could not fertilize the egg. There would need to be another mutation in males that would make sperm stronger, or secrete an enzyme that breaks down mucus, or something to that effect. However, look at Cystic Fibrosis. People used to die before adulthood. Most men with CF are sterile. Women with CF, living longer now because of better care and treatment, are getting pregnant, but many have a decreased lifespan post-pregnancy, and almost all the babies are premature. You can't predict "when" a series of beneficial mutations so dramatic as to change a being so dramatically. The answer might be never.

Try to give me a single or a few mutations that would prevent the ability of people from one population and another to mate. Say one mutation led to a smaller pelvis. Most women with that mutation would die in childbirth before a mutation arose to make smaller babies (which would most likely be a deleterious mutation as well).

I am not a geneticist (which is really the person who should be answering this question) but I think the odds of this scenario ever occurring are very low. I just can't imagine mutations making reproduction impossible between two populations being beneficial and selected in one population rather than harmful. Keep in mind that different humans from populations that were isolated for many thousands of years have no problem reproducing.

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  • $\begingroup$ just out of curiosity - why answer and vote to close? $\endgroup$ – AliceD Jan 13 '15 at 11:11
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    $\begingroup$ @ChrisStronks - ethical standards. :D $\endgroup$ – anongoodnurse Jan 13 '15 at 18:42

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