Genetic study reveals hidden chapter in human evolution
Genetic study reveals hidden chapter in human evolution
Modern humans descended from not one, but at least 2 ancestral populations that drifted apart and later reconnected, long before modern humans spread across
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Can some please let me understand how they are finding these miraculous genetic/DNA material long past their normal degradation times and how they are so sure that it belongs to humans or their ancestors? As far as I know DNA has 521 years half-life. So every 521 years you'll be losin 50% of the viable DNA without doing anything. So, by this math there shouldn't be any viable DNA in anything past couple thousand years but somehow we are keep finding miraculous DNA all over the place that goes back millions of years. When I read about these findings I see that they are talking about couple base pairs and best ones are talking about 120 base pairs. Considering human genome has over 3 billion base pairs how are these scientists are so sure about their findind?
They compared the entire genomes of 26 different modern human populations, and modeled their history to account for the patterns in the modern genomes.
For example, suppose a particular gene has two distinct groups within the modern genomes, with each group showing similar mutations within the group that are different from the mutations in the other group. You can infer that the two groups represent a split into two populations that later recombined, and you can infer the time of the split and the relative population sizes of the two groups from the number of mutations in each group.
Do that for the entire genome and you can make finer-grained inferences, like determining which genes experienced positive or negative selection pressure.
Thank you for your answer. Correct me if I'm wrong but this sounds like they are doing a lot of guess work in that. I'm really trying to wrap my head around it but basing your findings over 26 modern human populations and going back doesn't sound like solid way to go since you're looking for something you have and interpreting it based on that modern data while it can be something else and/or you're biased (like assuming that you have human DNA from dozen or more base pairs).
Also finding certain mutations sounds good but considering the rarity, the age of these findings, natural degradation and base pair counts in their findings makes it very iffy to believe it's exactly what they say it's. How can you be so lucky to find such discerning markers all the time and this consistently? It sounds improbable to me. I might be missing something in-between and I'm trying to find it but so far couldn't. If you or anyone else knows please let me know. Thanks in advance.
According to the paper, they tested ten different split-and-merge scenarios and this one was the most likely. But they give some important caveats, including:
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They assume that the smaller group had a more-or-less constant population size—if it fluctuated significantly, some of their other predictions on the dating of the split and merge might be off.
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They can’t rule out more complicated scenarios, like three or more splits and merges (but they can rule out the simpler scenario of no splits).
They do say that they tested their model on a number of other species (including chimps, bats, and dolphins), and got results consistent with those species’ known evolutionary histories.
So, basically they are working estimations, guesswork and their assumptions. I want to see the evidence that says yes this is what it's without any biased(all that estimations, guesswork and assumptions) information in it. This is my gripe with these DNA research. We share 98% or more of our DNA with a lot of other living beings yet these guys are like look here we found ATCG here and it must be human because we got this from human remains. While the human book is 3 billion letters long. What they found is open to all kind of interpretation and discussion but somehow nobody discuss these issues in this field.
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