At the risk of getting sidetracked, I saw an excellent Nat Geo documentary about 6 months ago called "The Search for Adam".
https://www.youtube.com/watch?v=LS2FMS87DE8
Essentially it is all about males will pass on a DNA marker to offspring, and based on where it is, you can tell how far back it goes. Now some of the more successful chains/conquerors from thousands of years ago (Ramses the Great or Genghis Khan for instance) will be present in a large percent of people, and working backwards, they were able to identify a single marker from ~60k years back that is present in everyone today. While obviously there were many ppl back then breeding, their ancestral lines eventually died out or blended in, which perhaps gives more credence to the "many breeds" hypothesis.
https://www.youtube.com/watch?v=LS2FMS87DE8
Essentially it is all about males will pass on a DNA marker to offspring, and based on where it is, you can tell how far back it goes. Now some of the more successful chains/conquerors from thousands of years ago (Ramses the Great or Genghis Khan for instance) will be present in a large percent of people, and working backwards, they were able to identify a single marker from ~60k years back that is present in everyone today. While obviously there were many ppl back then breeding, their ancestral lines eventually died out or blended in, which perhaps gives more credence to the "many breeds" hypothesis.