revelarts
12-06-2015, 12:37 AM
Nature Science Update (http://www.nature.com/news/2004/040927/full/040927-10.html) reported on a surprising find by Joseph Change (Yale) and Douglas Rohde (MIT). They claim, based on computer modeling of human breeding and migration, that we are all related to the same common ancestor, not millions, but just thousands of years ago, possibly just 1500 BC in Asia, and that perhaps a couple of thousand years before that, everyone alive at that time was an ancestor of all of us living today. The results are published in Nature Sept. 30.1
The finding is not entirely new; it is more a refinement of simpler models taking better account of migration and geographical isolation. It does not mean people didn’t exist before that, but only that the current population is genealogically related. Jotun Hein (Oxford) cautions in the same issue2 that genealogical questions are “distinct from questions about the history of our genetic material,” which are estimated by different methods: “Universal common ancestry (in the pedigree sense) and genetic common ancestry thus occur on different timescales,” he says.
If you think about it, it’s not all that surprising that in relatively few generations, a population’s family trees will overlap. Think of inverted pyramids that overlap slightly; as they grow (going back in time), they will all eventually converge, unless the populations are completely isolated, which does not seem to be the case for any people group. Simple models that assumed random mating converged in just 33 generations, or 800 years ago, which is clearly unrealistic. By taking geography and history into account, Hein says, Rohde has tried to arrive at a more credible date for the MRCA (most recent common ancestor). Even more surprising, Hein says, the models predict that before the MRCA, anyone alive would have been an ancestor of everyone alive today. Rohde, Olsen and Chang explain:
Given the remaining uncertainties about migration rates and real-world mating patterns, the date of the MRCA [most recent common ancestor] for everyone living today cannot be identified with great precision. Nevertheless, our results suggest that the most recent common ancestor for the world’s current population lived in the relatively recent past–perhaps within the last few thousand years. And a few thousand years before that, although we have received genetic material in markedly different proportions from the people alive at the time, the ancestors of everyone on the Earth today were exactly the same.
- See more at: http://crev.info/2004/09/human_common_ancestor_lived_3500_years_ago/#sthash.GogqwgtU.dpuf
The finding is not entirely new; it is more a refinement of simpler models taking better account of migration and geographical isolation. It does not mean people didn’t exist before that, but only that the current population is genealogically related. Jotun Hein (Oxford) cautions in the same issue2 that genealogical questions are “distinct from questions about the history of our genetic material,” which are estimated by different methods: “Universal common ancestry (in the pedigree sense) and genetic common ancestry thus occur on different timescales,” he says.
If you think about it, it’s not all that surprising that in relatively few generations, a population’s family trees will overlap. Think of inverted pyramids that overlap slightly; as they grow (going back in time), they will all eventually converge, unless the populations are completely isolated, which does not seem to be the case for any people group. Simple models that assumed random mating converged in just 33 generations, or 800 years ago, which is clearly unrealistic. By taking geography and history into account, Hein says, Rohde has tried to arrive at a more credible date for the MRCA (most recent common ancestor). Even more surprising, Hein says, the models predict that before the MRCA, anyone alive would have been an ancestor of everyone alive today. Rohde, Olsen and Chang explain:
Given the remaining uncertainties about migration rates and real-world mating patterns, the date of the MRCA [most recent common ancestor] for everyone living today cannot be identified with great precision. Nevertheless, our results suggest that the most recent common ancestor for the world’s current population lived in the relatively recent past–perhaps within the last few thousand years. And a few thousand years before that, although we have received genetic material in markedly different proportions from the people alive at the time, the ancestors of everyone on the Earth today were exactly the same.
- See more at: http://crev.info/2004/09/human_common_ancestor_lived_3500_years_ago/#sthash.GogqwgtU.dpuf