Faith writes:
I hope Taq or another geneticist will explain this. What I'd like explained among other things is how they get the 100,000 years by looking at DNA. Also what a DNA barcode is..
The DNA barcode they are talking about is a stretch of DNA from the mitochondrial genome (mtDNA). Mitochondria carry their own genomes that are separate from the genome in the cell nucleus, and it is passed down through maternal lineages because you inherit the mitochondria from the egg but not sperm.
The basic approach is to see how many differences there are between several mitochondrial genomes and then determine how long ago the common ancestor of those genomes lived by using the mutation rate and generation time. As it turns out, the most recent common ancestor (MRCA) for a lot of the species they looked at lived about 100,000 to 200,000 years. If they had looked at other genes in the autosomal genome (the DNA in the cell nucleus) I suspect they would have found a wide range of MRCAs for those genes.
Population genetics is my bag, but from what I think I do understand this isn't too much of a surprise. Even in a population of constant size you will get mitochondrial lineages that come to dominate a population over time. This is because not all mothers have daughters. Just by random luck you will get some mtDNA lineages that spread and become dominant and others that disappear. This is often called lineage sorting.
As the authors of the paper discuss, the simplest explanation is a population bottleneck for most species over the last 100,000 to 200,000 years, but they also state that there are other mechanisms, like lineage sorting, that could have produced the same observations.
https://phe.rockefeller.edu/...ckle-Thaler-Final-reduced.pdf
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