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[Gauge]

What evidence convinced YOU that all life traces back to a common ancestor?

[jimwalton]

I heard a lecture by a Christian geneticist, Dr. Stephen Schaffner (PhD from Yale in particle physics, now on staff with the Broad Institute of Harvard University and MIT), claiming that genetics do not confirm that all people originated from two people. I sent him an email for explanation, and he said, "As humans, humans, we all have lots of common ancestors, because if you go back far enough, anyone who's an ancestor to anyone is also an ancestor to everyone. One particular ancestor, the male who is ancestral to everyone by strictly male descent, is nicknamed Y-chromosome Adam, while the equivalent woman who is ancestral by strictly female descent is known as mitochondrial Eve. We descend from all of the other common ancestors by mixed male and female descent. For any given chunk of the genome, genetic diversity in the current human population is the result of mutations that have occurred since the last common ancestor for that chunk. If you know how often mutations occur, you can estimate how long ago the common ancestor lived. For almost the whole genome (which represents something like 150,000 independent chunks), this approach gives estimates on the order of a million years, give or take a few hundred thousand. For the Y-chromosome, which is inherited in the purely male line, the age of the most recent common ancestor is expected to be roughly one-quarter as old, and that’s what we find—something like a couple of hundred thousand years ago."