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I understand that the meaning of species as it stems from Linnaeus is unlikely to be useful in the DNA age Actually it is more useful than ever. Genetically t

I understand that the meaning of species as it stems from Linnaeus is unlikely to be useful in the DNA age Actually it is more useful than ever. Genetically there is no line in the sand between one species and all others. That's how everything evolves. Only practically do you have a chance to draw a line in the sand between two groups of animals. And keep in mind it is possible for A + B to have fertile offspring, and B + C too, but not A + C. Freaky, but that's biology for you. That's why a practical kludge like "fertile with itself, but not with others" is the best definition to use.

lifeisstillgood 14y ago
I see, everything smoothes out. But that makes my question more relevant the article, and the scientists behind it seem to be saying there is a line to draw, between Denisovia and Humans and Neanderthal. And they can draw that line with mtDNA * how can we distinguish between three species 41000 years ago * what are the metrics in DNA used (% of gene sequences different?) * if we are saying that xmillion yrs ago there was a common ancestor and they diverged into three species who evovled down till 40k yrs ago, then how can we call them different species if we were still interbreeding 40k ago? If we were interbreeding then we were same species, so again what is the DNA based reason for saying seperate species? One last thing - if the A+B scenarios imply that say humans bred with Neanderthal and their offspring had to breed with denisovians whose offspring then could bring DNA back to human line, (while human/denisovians could never produce fertile offspring) then I still see the same issue if we interbreed we are same species, so what is the DNA based rationale for saying no we weren't if we were not interbreeding ... It makes more sense but presumably the mutations in different trees got shared after common ancestor ? Edit: tokenadult kindly re-edited and I did not spot it I time but makes the point that DNA definition of different species in Pre history is weak at best, and relies on other Indixators of breeding success. I shall assume that the "DNA shows a different species" to be poor science journalism rather than poor science and bookmark this for further Reading later apologies for any iPhone based typos. Edit again: Just checking: If we find two skeletons 250k yrs old, definitetly Neanderthal and human, sequence their genomes. Then find two skeletons at 150k one has acquired a random mtDNA mutation and then find the same mutation on both at 50k years ago - then can we estimate the odds of that being mutally independnt mutations? And is that what this branch of science is trying to do? (I remember Leakey being quoted as saying we have only found enough ancient skeleton bones to fit in the back of his car, so the above convenient pairs of skeletons are understandably hypothetical) pps HN and iPhones do not get on so if this editlooksawful I am justleaving it - thank you for the comments - always nice to have questions treated seriously - and thanks to tokenadult again for living upto your handle
- fghh45sdfhr3 14y ago
  the article, and the scientists behind it seem to be saying there is a line to draw, between Denisovia and Humans and Neanderthal. There is a line because you can differentiate between almost any two groups of people using DNA. Ashkenazim Jews versus other Jews for example. That obviously does not make them different species, it just means you can separate the two groups with enough math, like principal component analysis. That's why the quoted scientist in the article says: "It was the first time a new group of distinct humans was discovered" A new group of humans. what are the metrics in DNA used That information is hopefully in their paper. Usually it's some fairly straightforward statistics. how can we call them different species if we were still interbreeding 40k ago? I think we call them different species because the status quo used to be that we never interbred with them. We couldn't find any Neanderthal mtDNA in humans, despite the strong archeology evidence that we had contact with them. As DNA technology kept improving, we were able to recover more DNA from ancient samples, and looked at the Y chromosome, and surprise you might have enough Neanderthal DNA to count as full grand, grand father! So I think at this point, we can't call them a separate species any more. But inertia being what it is, we keep doing it. Also it makes for more eye catching article headlines. while human/denisovians could never produce fertile offsprin That was just my example about how we define species. According to the article: "...but the evidence also suggests that Denisovans and humans interbred." can we estimate the odds of that being mutally independnt mutation Yeah, that's kind of what they are doing. It is heavily based on statistical estimation and that's why when then guess the age of a sample it is between A LOT of years. They know their error margin is large.
  - lifeisstillgood 14y ago
    Thank you, some reading to do, starting with the actual paper. Cheers

lifeisstillgood 14y ago

I see, everything smoothes out. But that makes my question more relevant the article, and the scientists behind it seem to be saying there is a line to draw, between Denisovia and Humans and Neanderthal. And they can draw that line with mtDNA * how can we distinguish between three species 41000 years ago * what are the metrics in DNA used (% of gene sequences different?) * if we are saying that xmillion yrs ago there was a common ancestor and they diverged into three species who evovled down till 40k yrs ago, then how can we call them different species if we were still interbreeding 40k ago? If we were interbreeding then we were same species, so again what is the DNA based reason for saying seperate species? One last thing - if the A+B scenarios imply that say humans bred with Neanderthal and their offspring had to breed with denisovians whose offspring then could bring DNA back to human line, (while human/denisovians could never produce fertile offspring) then I still see the same issue if we interbreed we are same species, so what is the DNA based rationale for saying no we weren't if we were not interbreeding ... It makes more sense but presumably the mutations in different trees got shared after common ancestor ? Edit: tokenadult kindly re-edited and I did not spot it I time but makes the point that DNA definition of different species in Pre history is weak at best, and relies on other Indixators of breeding success. I shall assume that the "DNA shows a different species" to be poor science journalism rather than poor science and bookmark this for further Reading later apologies for any iPhone based typos. Edit again: Just checking: If we find two skeletons 250k yrs old, definitetly Neanderthal and human, sequence their genomes. Then find two skeletons at 150k one has acquired a random mtDNA mutation and then find the same mutation on both at 50k years ago - then can we estimate the odds of that being mutally independnt mutations? And is that what this branch of science is trying to do? (I remember Leakey being quoted as saying we have only found enough ancient skeleton bones to fit in the back of his car, so the above convenient pairs of skeletons are understandably hypothetical) pps HN and iPhones do not get on so if this editlooksawful I am justleaving it - thank you for the comments - always nice to have questions treated seriously - and thanks to tokenadult again for living upto your handle

fghh45sdfhr3 14y ago
the article, and the scientists behind it seem to be saying there is a line to draw, between Denisovia and Humans and Neanderthal. There is a line because you can differentiate between almost any two groups of people using DNA. Ashkenazim Jews versus other Jews for example. That obviously does not make them different species, it just means you can separate the two groups with enough math, like principal component analysis. That's why the quoted scientist in the article says: "It was the first time a new group of distinct humans was discovered" A new group of humans. what are the metrics in DNA used That information is hopefully in their paper. Usually it's some fairly straightforward statistics. how can we call them different species if we were still interbreeding 40k ago? I think we call them different species because the status quo used to be that we never interbred with them. We couldn't find any Neanderthal mtDNA in humans, despite the strong archeology evidence that we had contact with them. As DNA technology kept improving, we were able to recover more DNA from ancient samples, and looked at the Y chromosome, and surprise you might have enough Neanderthal DNA to count as full grand, grand father! So I think at this point, we can't call them a separate species any more. But inertia being what it is, we keep doing it. Also it makes for more eye catching article headlines. while human/denisovians could never produce fertile offsprin That was just my example about how we define species. According to the article: "...but the evidence also suggests that Denisovans and humans interbred." can we estimate the odds of that being mutally independnt mutation Yeah, that's kind of what they are doing. It is heavily based on statistical estimation and that's why when then guess the age of a sample it is between A LOT of years. They know their error margin is large.
- lifeisstillgood 14y ago
  Thank you, some reading to do, starting with the actual paper. Cheers