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Geographically isolated humans, any significant evolution?

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    I was curious to know about any evolution in such geographically isolated groups such as those in the South American rainforest for example.

    Considering they've been isolated for thousands of years, possibly tens of thousands (correct me if I'm wrong), and because of allopatric speciation, we are told that evolution is probable, given time. Has there been any significant changes due to genetic drifting amongst other factors between us?

    They do not look much different than us really, so what other factors do we need to consider?

    And how much time do you really need when we say "given time"?
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    I don't know off hand of major changes among people in this situation. The only one I know if is their ability to run in bare feet. Because we use shoes the underside of our feet and lower legs have become weaker, but tribes in the middle of nowhere can run for miles in bare feet without issue. Not sure if that counts.
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    (Original post by G8D)
    I doubt that they'd have churned through enough generations or been faced with enough environmental differences to have deviated any great amount.
    How many generations are needed? They have been isolated for thousands possibly tens of thousands no?

    And how extreme do the environmental differences need to be? We're talking about an environment near the equator, compared to those dry environments in Africa and then the cold and harsh environment up north.

    And due to the barriers of the oceans for such a long time, allopatric speciation should have taken place and they should now be a completely new species?

    The gene pools should be different between us due to genetic drifting with such a long period of time, so surely they should now be a new species?

    EDIT: Also, if we are to take the finches as an example, within such a close environment at the islands, I'm pretty sure environmental factors between humans is much larger.

    (Original post by Bilco)
    I don't know off hand of major changes among people in this situation. The only one I know if is their ability to run in bare feet. Because we use shoes the underside of our feet and lower legs have become weaker, but tribes in the middle of nowhere can run for miles in bare feet without issue. Not sure if that counts.
    That's an interesting variation.

    However, I'm talking about allopatric speciation, with that amount of time, shouldn't they now be a new species?
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    (Original post by TheGrinningSkull)
    with that amount of time, shouldn't they now be a new species?
    Why don't you have unprotected sex with one of the tribal daughters and see? If you produce fertile offspring, you're not a different species.

    I hope you like hairy women. :unsure:
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    (Original post by TheGrinningSkull)
    However, I'm talking about allopatric speciation, with that amount of time, shouldn't they now be a new species?

    No. New species would occur after millions of years, and they've only been a separate tribe living in the Amazon for as long as humans have been truly sentient, so like, a couple of thousand years at the most.
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    (Original post by Electronica)
    Why don't you have unprotected sex with one of the tribal daughters and see? If you produce fertile offspring, you're not a different species.

    I hope you like hairy women. :unsure:
    I wasn hoping someone on tsr would take the challenge
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    (Original post by wanderlust.xx)
    No. New species would occur after millions of years, and they've only been a separate tribe living in the Amazon for as long as humans have been truly sentient, so like, a couple of thousand years at the most.
    How do you know that millions of years is required?

    This link may be of interest: http://www.nature.com/news/2009/0911...2009.1089.html

    The link also mentions reproductive isolation as the species concerned is not really geographically isolated. So how is it that a new species (possibly), could arise so quickly?

    Also, with such small tribes, genetic drift would be more probable.
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    (Original post by TheGrinningSkull)
    I wasn hoping someone on tsr would take the challenge
    Challenge accepted.
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    "It has not been demonstrated that any human breeding population is sufficiently divergent to be taxonomically recognized by the standards of modern molecular systematics" (Keita et al., 2004).

    "[...], human evolution has been and is characterized by many locally differentiated populations coexisting at any given time, but with sufficient genetic contact to make all of humanity a single lineage sharing a common evolutionary fate" (Templeton, 1998).

    "Our results show that when individuals are sampled homogeneously from around the globe, the pattern seen is one of gradients of allele frequencies that extend over the entire world, rather than discrete clusters" (Serre & Pääbo, 2004).

    No.
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    (Original post by TheGrinningSkull)
    How many generations are needed? They have been isolated for thousands possibly tens of thousands no?

    And how extreme do the environmental differences need to be? We're talking about an environment near the equator, compared to those dry environments in Africa and then the cold and harsh environment up north.

    And due to the barriers of the oceans for such a long time, allopatric speciation should have taken place and they should now be a completely new species?
    I think you also have to take into account that humans are originally an African species - it's not the isolated groups in that sort of area you'd expect to evolve much because they're facing the same environmental pressures they have for millions of years previously, but the humans who left that area and spread around the rest of the world. And the thing is, we've largely beaten out environmental factors with technology - instead of evolving to face colder climates, we wear clothes, for example.

    Also, generally speaking, we've had more genetic contact with each other around the world than other species can boast, again largely because of technology (even going back over a thousand years, small numbers of european explorers - vikings, - reached the Americas, for example). A brain that isn't too big or too small, opposable thumbs and being a group animal (working together to hunt and so on) are a highly useful combination which between them allow us to adapt to all sorts of environments and challenges without physically changing very much. Obviously there's been some change - skin colour being the most obvious - but no real significant changes.
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    (Original post by TheGrinningSkull)
    However, I'm talking about allopatric speciation, with that amount of time, shouldn't they now be a new species?
    If you are talking on a level of speciation it's highly unlikely something like that would occur for a species like ours over that period of time. Bare in mind although groups are isolated the conditions they face are not much different than everywhere else less than 1000 years ago. An instant in evolutionary time. Given enough time and assuming technological advancement, sure. At this point it wouldn't be, imo, expected.
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    (Original post by Bilco)
    If you are talking on a level of speciation it's highly unlikely something like that would occur for a species like ours over that period of time. Bare in mind although groups are isolated the conditions they face are not much different than everywhere else less than 1000 years ago. An instant in evolutionary time. Given enough time and assuming technological advancement, sure. At this point it wouldn't be, imo, expected.
    Although, it's been more than 1000 years, possibly tens of thousands for south American tribes say.
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    (Original post by Concept186)
    I think you also have to take into account that humans are originally an African species - it's not the isolated groups in that sort of area you'd expect to evolve much because they're facing the same environmental pressures they have for millions of years previously, but the humans who left that area and spread around the rest of the world. And the thing is, we've largely beaten out environmental factors with technology - instead of evolving to face colder climates, we wear clothes, for example.

    Also, generally speaking, we've had more genetic contact with each other around the world than other species can boast, again largely because of technology (even going back over a thousand years, small numbers of european explorers - vikings, - reached the Americas, for example). A brain that isn't too big or too small, opposable thumbs and being a group animal (working together to hunt and so on) are a highly useful combination which between them allow us to adapt to all sorts of environments and challenges without physically changing very much. Obviously there's been some change - skin colour being the most obvious - but no real significant changes.
    Hmm, some good points, although for those that have reached the Americas, it would've been north America mostly, and areas in the Amazon rainforest would've been undiscovered and those many tribes would have been completely isolated for more than thousands of years. Would these tribes have had genetic contact with explorers not so relatively long ago?
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    (Original post by whyumadtho)
    "It has not been demonstrated that any human breeding population is sufficiently divergent to be taxonomically recognized by the standards of modern molecular systematics" (Keita et al., 2004).

    "[...], human evolution has been and is characterized by many locally differentiated populations coexisting at any given time, but with sufficient genetic contact to make all of humanity a single lineage sharing a common evolutionary fate" (Templeton, 1998).

    "Our results show that when individuals are sampled homogeneously from around the globe, the pattern seen is one of gradients of allele frequencies that extend over the entire world, rather than discrete clusters" (Serre & Pääbo, 2004).

    No.
    How sufficient is sufficient genetic contact? Surely tribes isolated for many 1000s of years, and due to cultural differences, possibly even reproductive isolation taking placee in line with geographical isolation, genetic contact would've been minimal if not non-existent?

    Regarding individuals sampled, did these samples include isolated groups?
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    Geographical isolation often isn't enough for speciation to occur, especially when you're only talking in terms of thousands of year. For them to have become a new species they would have needed to have really strong selection pressures or a big sweep of genetic drift to push their population towards becoming a different species :/ Humans are notoriously unaffected by selection pressures on phenotypes, as we use tools etc to combat physical disadvantages.
    Even without genetic input from the outside, the small populations are probably just recycling the same gene pool, and in fact a lack of variation is probably keeping them from becoming a new species.

    You probably would see some phenotypic advantages amongst their members though, like you do in people who live at high altitudes having a higher affinity to oxygen, and some tribes in polynesia have strengthened eye muscles as their life style involves fishing underwater. These difference have probably been selected for in the same time frame as the one you're considering for these tribes.
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    (Original post by TheGrinningSkull)
    Although, it's been more than 1000 years, possibly tens of thousands for south American tribes say.
    Yes and you are talking about a process which takes millions and millions of years. When you account for technology and climate it would take even longer if it would happen at all. We are also a species where evolution is slower than say a fly.
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    (Original post by Cariie)
    Geographical isolation often isn't enough for speciation to occur, especially when you're only talking in terms of thousands of year. For them to have become a new species they would have needed to have really strong selection pressures or a big sweep of genetic drift to push their population towards becoming a different species :/ Humans are notoriously unaffected by selection pressures on phenotypes, as we use tools etc to combat physical disadvantages.
    Even without genetic input from the outside, the small populations are probably just recycling the same gene pool, and in fact a lack of variation is probably keeping them from becoming a new species.

    You probably would see some phenotypic advantages amongst their members though, like you do in people who live at high altitudes having a higher affinity to oxygen, and some tribes in polynesia have strengthened eye muscles as their life style involves fishing underwater. These difference have probably been selected for in the same time frame as the one you're considering for these tribes.
    How is that so, when we are told that geographical isolation is the most important in evolution?.

    With a small gene pool recycling itself for so many thousands of years, how have they even managed to survive for so long?
    I would've thought that mutations were more likely to occur.

    Also, possibly looking at it from the other perspective, if lack of variation is stopping them from evolving, have we, then, evolved relative to the isolated groups?
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    (Original post by TheGrinningSkull)
    Hmm, some good points, although for those that have reached the Americas, it would've been north America mostly, and areas in the Amazon rainforest would've been undiscovered and those many tribes would have been completely isolated for more than thousands of years. Would these tribes have had genetic contact with explorers not so relatively long ago?
    True about the South Americas to an extent - evidence of humans in South America goes back about 12,000 years ish, which I think is also about when land access between the old and new worlds stopped.

    Thing is, if you want significant enough genetic change over that short a timescale - remembering that some species, like the Coelacanth, have remained unchanged in their niches for hundreds of millions of years - then you're looking for significant evolutionary pressures that existing human traits couldn't have dealt with - and I'd dispute whether South America presents anything that humans at the time couldn't already have dealt with. Human populations in south america were large enough that genetic drift on it's own is unlikely to have any real impact - there were multiple, sizeable pre-columbian civilisations. We're certainly not talking about truly isolated small groups - most of what you'd refer to as "uncontacted tribes" are descended from peoples who were part of one civilization or another until said civilization collapsed sometime in relatively recent history, and then people largely forget about them - look at Incan sites for example, inhabited until ~1500 AD then some were completely forgotten for 400 years.

    Tl;dr, South American lack of speciation can easily be explained by the same ways as European lack of speciation - large scale civilisations meaning that the population was large enough to avert genetic drift, and advanced enough with tools, farming etc to negate any real selection pressures. The only difference is, you seem to have forgotten about those civilizations because the most recent collapsed 500 years ago.

    (Original post by TheGrinningSkull)
    How sufficient is sufficient genetic contact? Surely tribes isolated for many 1000s of years, and due to cultural differences, possibly even reproductive isolation taking placee in line with geographical isolation, genetic contact would've been minimal if not non-existent?
    The thing is, there aren't really instances of groups of humans that were both isolated from the rest for evolutionary significant periods of time and existed in small enough groups for genetic drift to do anything, nor have there been significant selection pressures that humans can't already deal with thanks to tool usage and suchlike. As I said, your "uncontacted tribes" have, pretty much exclusively speaking, only been as isolated as they are for less than a thousand years.
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    (Original post by Bilco)
    Yes and you are talking about a process which takes millions and millions of years. When you account for technology and climate it would take even longer if it would happen at all. We are also a species where evolution is slower than say a fly.
    Hmm, that's a good point I guess, guess we'll have to wait and see
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    (Original post by TheGrinningSkull)
    How is that so, when we are told that geographical isolation is the most important in evolution?.
    You're confusing the importance of isolation with its ability to act as a mechanism. Geographical isolation doesn't cause variation itself, it's just important in allowing variation caused by the actual mechanisms to gain prominence in a gene pool. If those mechanisms can't generate sufficient variation for the numerous reasons mentioned by people above, then isolation is irrelevant.

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