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Early humans may have bred with other species – twice

14 points by fun2have 16y ago

pg 16y ago
Both of these events happened outside of Africa. Are they saying that the descendants of these interbreedings propagated back into Africa afterward? Or are they saying not everyone has this in their DNA?
- deleted 16y ago
  [deleted]
- pchristensen 16y ago
  Probably the latter: "As humans began fanning out from Africa, between 50 and 100,000 years ago, these markers changed. A team ... found evidence that some of the markers looked far too old to have come from humans."
- bh42 16y ago
  From: http://www.nature.com/news/2010/100420/full/news.2010.194.html http://www.nature.com/news/2010/100420/full/news.2010.194.ht... ...the interbreeding happened about 60,000 years ago in the eastern Mediterranean and, more recently, about 45,000 years ago in eastern Asia. Those two events happened after the first H. sapiens had migrated out of Africa, says Long. His group didn't find evidence of interbreeding in the genomes of the modern African people included in the study. I find this very surprising. We know that there was a genetic bottle neck when we left Africa. This is why today people from two different African ethnic groups can be MORE different then any two people from ANYWHERE in the rest of the world. An Inuit and an South American Indian are genetically more similar then a Touareg and a Lemba. How could a separate species like the Neanderthals, who spent 200 thousand years in isolation in ice age Europe, contribute so little genetic diversity?
  - btilly 16y ago
    How could a separate species like the Neanderthals, who spent 200 thousand years in isolation in ice age Europe, contribute so little genetic diversity? A single successful interbreeding incident would contribute some odd genes to the local gene pool, but wouldn't contribute much genetic diversity once it spread out through the local gene pool. Remember that the data suggests exactly 2 individuals dropped into human populations that were locally in the tens of thousands, and globally in the multiple hundreds of thousands. It would contribute some odd genes to the pool of genetic diversity, but wouldn't move the bar very much. For those who think that species barriers are some sort of absolute barrier to what is hypothesized here, it is worth considering the case of donkeys, horses and mules. Donkeys and horses are estimated to have diverged a couple of million years ago, but routinely can breed. The result are mules, of which over time we've bred tens of millions.. Mules are almost invariably infertile. However according to http://en.wikipedia.org/wiki/Mule#Fertility http://en.wikipedia.org/wiki/Mule#Fertility there have been more than 60 documented cases of female mules successfully bred by stallions. The foals would be mostly horse, and the result of that is an animal that is 3/4 horse which therefore is likely to be able to breed with other horses. It is not unreasonably by comparison that there could be a constant level of interbreeding between us and Neanderthals, with many infertile offspring, and by chance on 2 occasions fertile offspring who have descendants today. (The overall number of crossbreeds would be lower than the number of mules, but their odds of fertility would be much higher than for mules.)
    - netcan 16y ago
      This would also suggest a reasonable chance that some hybrids bred back into the Neanderthal populations instead of ours.
      - btilly 16y ago
        Odds are high that those hybrids are now evolutionarily irrelevant.
    - bh42 16y ago
      Remember that the data suggests exactly 2 individuals dropped into human populations that were locally in the tens of thousands I did not notice that, but it seems that's just what we have detected so far. If it can happen twice, isn't it very likely it would happen quite a few times? As to species barriers, by definition a species is what is reproductively isolated. Biology is not nearly as clean as say math, and so reproductive isolation is quite blurry. Some times A + B works and B + C works but A and C are reproductively isolated. Often, A + B makes, C and C + (C or A or B) makes D, but D is infertile. Or E is infertile. And while A + B makes C and even D and E, the fact that the lines eventually terminate means A and B are reproductively isolated. The foals would be mostly horse, and the result of that is an animal that is 3/4 horse which therefore is likely to be able to breed with other horses. Not so. It is true that once in a million a fertile mule is born, but that mule's offspring are not fertile, or its grandchildren are not fertile. Mules have been bred throughout history, but I know of no line of mostly donkey or horse hybrids with a fertile mule parent, or gand, or grand-grand-grand parent, or any mule linage. and by chance on 2 occasions fertile offspring But that in no way guarantees THEIR offspring with either Humans or Neanderthals (or other hybrids) would be fertile or that their grandchildren would be. And if they were, then by definition us and Neanderthals are the same species. And in that case I still don't understand how there could be so little genetic difference contributed. For sweet zombie jesus' sake, we can identify the descendants of a Central Asian male who lived around the time of Genghis Khan over most of Eurasia. And successful interbreeding with a population who lived apart for 200 THOUSAND freaking years leaves only a few stray genes?
Anon84 16y ago
Other events were already known, like the "Lapedo child" in Portugal: http://en.wikipedia.org/wiki/Lapedo_child http://en.wikipedia.org/wiki/Lapedo_child
- bh42 16y ago
  I find the current state of that wikipedia page questionable. Refutes is a very strong term. Humans and Neanderthals look very similar and children have different proportions AND the differences between individuals are great thus the inference you can make from just ONE sample does not warrant terms like "refutes".
DrSprout 16y ago
>If humans bred only with other humans, all these markers would create a neat phylogenetic tree, showing that human genetic diversity can be traced to a single population that existed in Africa in the last 100,000 years. I'm not a statistician, but from what I've studied of genetics, that seems like an unwarranted leap. Phylogenetic trees, at the end of the day, are guesswork (though they probably reflect reality pretty closely.) If you have a neat phylogenetic tree, you've probably been massaging your data.
bh42 16y ago
More details here: http://www.nature.com/news/2010/100420/full/news.2010.194.html http://www.nature.com/news/2010/100420/full/news.2010.194.ht... The ancient mitochondrial DNA came from a piece of finger bone, which the groups haven't identified by species. It could be Neanderthal, a new Homo species or some other archaic form — like H. erectus, who spread to Oceania by 1.8 million years ago. . But the age of the bone has been questioned by researchers, who say the cave's sediments may have been reworked, making the bone's layer older. Could the bone turn out to be much older?

14 points by fun2have 16y ago

pg 16y ago

Both of these events happened outside of Africa. Are they saying that the descendants of these interbreedings propagated back into Africa afterward? Or are they saying not everyone has this in their DNA?

deleted 16y ago
[deleted]
pchristensen 16y ago
Probably the latter: "As humans began fanning out from Africa, between 50 and 100,000 years ago, these markers changed. A team ... found evidence that some of the markers looked far too old to have come from humans."
bh42 16y ago
From: http://www.nature.com/news/2010/100420/full/news.2010.194.html http://www.nature.com/news/2010/100420/full/news.2010.194.ht... ...the interbreeding happened about 60,000 years ago in the eastern Mediterranean and, more recently, about 45,000 years ago in eastern Asia. Those two events happened after the first H. sapiens had migrated out of Africa, says Long. His group didn't find evidence of interbreeding in the genomes of the modern African people included in the study. I find this very surprising. We know that there was a genetic bottle neck when we left Africa. This is why today people from two different African ethnic groups can be MORE different then any two people from ANYWHERE in the rest of the world. An Inuit and an South American Indian are genetically more similar then a Touareg and a Lemba. How could a separate species like the Neanderthals, who spent 200 thousand years in isolation in ice age Europe, contribute so little genetic diversity?
- btilly 16y ago
  How could a separate species like the Neanderthals, who spent 200 thousand years in isolation in ice age Europe, contribute so little genetic diversity? A single successful interbreeding incident would contribute some odd genes to the local gene pool, but wouldn't contribute much genetic diversity once it spread out through the local gene pool. Remember that the data suggests exactly 2 individuals dropped into human populations that were locally in the tens of thousands, and globally in the multiple hundreds of thousands. It would contribute some odd genes to the pool of genetic diversity, but wouldn't move the bar very much. For those who think that species barriers are some sort of absolute barrier to what is hypothesized here, it is worth considering the case of donkeys, horses and mules. Donkeys and horses are estimated to have diverged a couple of million years ago, but routinely can breed. The result are mules, of which over time we've bred tens of millions.. Mules are almost invariably infertile. However according to http://en.wikipedia.org/wiki/Mule#Fertility http://en.wikipedia.org/wiki/Mule#Fertility there have been more than 60 documented cases of female mules successfully bred by stallions. The foals would be mostly horse, and the result of that is an animal that is 3/4 horse which therefore is likely to be able to breed with other horses. It is not unreasonably by comparison that there could be a constant level of interbreeding between us and Neanderthals, with many infertile offspring, and by chance on 2 occasions fertile offspring who have descendants today. (The overall number of crossbreeds would be lower than the number of mules, but their odds of fertility would be much higher than for mules.)
  - netcan 16y ago
    This would also suggest a reasonable chance that some hybrids bred back into the Neanderthal populations instead of ours.
    - btilly 16y ago
      Odds are high that those hybrids are now evolutionarily irrelevant.
  - bh42 16y ago
    Remember that the data suggests exactly 2 individuals dropped into human populations that were locally in the tens of thousands I did not notice that, but it seems that's just what we have detected so far. If it can happen twice, isn't it very likely it would happen quite a few times? As to species barriers, by definition a species is what is reproductively isolated. Biology is not nearly as clean as say math, and so reproductive isolation is quite blurry. Some times A + B works and B + C works but A and C are reproductively isolated. Often, A + B makes, C and C + (C or A or B) makes D, but D is infertile. Or E is infertile. And while A + B makes C and even D and E, the fact that the lines eventually terminate means A and B are reproductively isolated. The foals would be mostly horse, and the result of that is an animal that is 3/4 horse which therefore is likely to be able to breed with other horses. Not so. It is true that once in a million a fertile mule is born, but that mule's offspring are not fertile, or its grandchildren are not fertile. Mules have been bred throughout history, but I know of no line of mostly donkey or horse hybrids with a fertile mule parent, or gand, or grand-grand-grand parent, or any mule linage. and by chance on 2 occasions fertile offspring But that in no way guarantees THEIR offspring with either Humans or Neanderthals (or other hybrids) would be fertile or that their grandchildren would be. And if they were, then by definition us and Neanderthals are the same species. And in that case I still don't understand how there could be so little genetic difference contributed. For sweet zombie jesus' sake, we can identify the descendants of a Central Asian male who lived around the time of Genghis Khan over most of Eurasia. And successful interbreeding with a population who lived apart for 200 THOUSAND freaking years leaves only a few stray genes?

Anon84 16y ago

Other events were already known, like the "Lapedo child" in Portugal: http://en.wikipedia.org/wiki/Lapedo_child http://en.wikipedia.org/wiki/Lapedo_child

bh42 16y ago
I find the current state of that wikipedia page questionable. Refutes is a very strong term. Humans and Neanderthals look very similar and children have different proportions AND the differences between individuals are great thus the inference you can make from just ONE sample does not warrant terms like "refutes".

DrSprout 16y ago

>If humans bred only with other humans, all these markers would create a neat phylogenetic tree, showing that human genetic diversity can be traced to a single population that existed in Africa in the last 100,000 years. I'm not a statistician, but from what I've studied of genetics, that seems like an unwarranted leap. Phylogenetic trees, at the end of the day, are guesswork (though they probably reflect reality pretty closely.) If you have a neat phylogenetic tree, you've probably been massaging your data.

bh42 16y ago

More details here: http://www.nature.com/news/2010/100420/full/news.2010.194.html http://www.nature.com/news/2010/100420/full/news.2010.194.ht... The ancient mitochondrial DNA came from a piece of finger bone, which the groups haven't identified by species. It could be Neanderthal, a new Homo species or some other archaic form — like H. erectus, who spread to Oceania by 1.8 million years ago. . But the age of the bone has been questioned by researchers, who say the cave's sediments may have been reworked, making the bone's layer older. Could the bone turn out to be much older?