Genetic Atlas of Human Mixing Events Traces Ancestry

Nicholas Wade published an article in The New York Times on February 13, 2014 about geneticists creating a genetic atlas of human mixing events in order to trace ancestry. Many events have led to a complex mixing of populations all over the world. Geneticists are trying a new statistical approach that would identify major mixing events over the last 4000 years. This would also help assist historians. For example, geneticists have found that people of the Southern Mediterranean and the Middle East have origins in Africa due to genomes inserted between A.D. 650 and 1900. This was caused by the Arab slave trade. European DNA mixed into the Kalash population between 990 and 210 B.C. partially because of the Indian invasion in 326 B.C. by Alexander the Great. An article was published in the journal titled, Science, on the genetic atlas of human mixing. Simon Myers, Garrett Hellenthal, Daniel Falush, and their team sampled genomes from around the world. They determined that there are about 95 distinguished populations. People of different populations have genomes with unique mutations. Based on the differences in a person's DNA sequence in their genome, scientists can tell what race or population their ancestry is. Dr. Myers developed a statistical technique that identifies the chromosomal segments that hint at when the mixing event took place. This is possible by measuring the length of the chromosome segments of a specific ancestry in a population. In successive generations, the length becomes smaller because DNA is traded between the parents' genomes when making an egg or sperm. Dr. Myers and his team have posted more records of the degree of admixture in each populations on their website.

Left: With each generation, the DNA segments get smaller.
Right: Circles show DNA sources from European and Asian parent populations. The black dot represents the Kalash people of Pakistan. 

The genetic atlas of human mixing events is only reliable if the populations vary greatly. This system is not accurate enough to distinguish between similar populations. I am always skeptical of anything that dates back that far in history. I would like to see the evidence determining what the DNA of certain populations looked like so many years ago. I tend not to believe things that I cannot physically see so this is something that I would have to research more before I believe Dr. Myers.