One point that has always boggled my n00b understanding of this field is what unit of measure geneticists are using when they speak of humans and chimps being 99% the same genetically, but then also say that modern humans have 2-4% DNA in common with Neandersovans?
Clearly those two statements are each using a radically different metric, which never seems to be explained! (/old man yells at the clouds)
A further noob question I can't figure in my mind is exactly how humans have decent amounts of neanderthal and denisovan DNA intermixed but zero mtDNA introgression? What are the scenarios in which that happens? Is it only males of these other human groups intermixing? Is it mothers staying with their children in their own groups and thus the mtDNA from neanderthal/denisovan mothers disappeared with their groups/cultures?
Great summary article this one Razib. I have some keen multi-regionalist friends and a couple of things that always come up in conversations that I think I have answers to but curious on your take.
1. Some research suggests that some mtDNA can sometimes come from the male line. To me that would add some variation and if anything make the date to a common female ancestor look deeper in time than it really is? The small amount of potential added variation would not greatly alter the story though even if possible.
2. What about the possibility that extra variation was inherited from European migration back into Africa? To my mind that would then require all those Europeans to have left no genetic trace back in Europe if is to look like unique variation in African populations. They then posit the plague as something that would have then depleted European variation. To me this would require much more than the plague to have European mtDNA variation so reduced relative to African variation.
IANaG (I am not a geneticist, or even a biologist), so take this FWIW. What I got out of reading David Reich's book is that our current technology cannot see differences in the mtDNA going back more than 160,000 years (to the origin of H sapiens sapiens as a distinct species). I.e., at that distance they all look the same. I do not know whether the issue is our limited techniques or that there is not enough codons from which to extract the information.
One point that has always boggled my n00b understanding of this field is what unit of measure geneticists are using when they speak of humans and chimps being 99% the same genetically, but then also say that modern humans have 2-4% DNA in common with Neandersovans?
Clearly those two statements are each using a radically different metric, which never seems to be explained! (/old man yells at the clouds)
Can anybody enlighten me please?
What is a 2000-year-old mtDNA molecule like? Is it still a circle? Is it still inside of a mitochondrion?
A further noob question I can't figure in my mind is exactly how humans have decent amounts of neanderthal and denisovan DNA intermixed but zero mtDNA introgression? What are the scenarios in which that happens? Is it only males of these other human groups intermixing? Is it mothers staying with their children in their own groups and thus the mtDNA from neanderthal/denisovan mothers disappeared with their groups/cultures?
Great summary article this one Razib. I have some keen multi-regionalist friends and a couple of things that always come up in conversations that I think I have answers to but curious on your take.
1. Some research suggests that some mtDNA can sometimes come from the male line. To me that would add some variation and if anything make the date to a common female ancestor look deeper in time than it really is? The small amount of potential added variation would not greatly alter the story though even if possible.
2. What about the possibility that extra variation was inherited from European migration back into Africa? To my mind that would then require all those Europeans to have left no genetic trace back in Europe if is to look like unique variation in African populations. They then posit the plague as something that would have then depleted European variation. To me this would require much more than the plague to have European mtDNA variation so reduced relative to African variation.
IANaG (I am not a geneticist, or even a biologist), so take this FWIW. What I got out of reading David Reich's book is that our current technology cannot see differences in the mtDNA going back more than 160,000 years (to the origin of H sapiens sapiens as a distinct species). I.e., at that distance they all look the same. I do not know whether the issue is our limited techniques or that there is not enough codons from which to extract the information.