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May 21, 2010
Deep Ancestry
Deep Ancestry Inside the Genographic Project, by Spencer Wells, copyright 2006, publisher National Geographic Society, 247 pages.
Our genes, our DNA, contain information about our ancestry, about our differences from others and our relatedness to them. If enough of this information from many, many individuals in geographically dispersed areas is analyzed together we can learn a great deal about the development and migrations of our species.
Spencer Wells is both a solid scientist and a great promoter, a guy who could sell swamp land in Florida. He is using his skills to generate wide recognition and enthusiasm for the Genographic Project and the National Geographic Society.
The genographic project essentially involves taking chromosome samples (by swabbing the inside of the cheek) from thousands of people all over the world, then comparing and analyzing. The particular chromosomes which are analyzed are the mitochondria, which are passed on only from mother to children, and the Y which is passed on only from father to sons. These two types of chromosomes are not mixed and matched with chromosomes from both parents which happens at conception with all the other chromosomes. Because of that, they are passed on intact and any changes observed between the chromosomes of two people are due to mutations occurring infrequently over a number of generations.
These mutations can tell us roughly how many generations ago two individuals shared the same ancestor. Also, by looking at larger populations and where the mutations are most prevalent, we can make well-informed guesses of the region of the world where that ancestor lived. I don't want to say a lot more. For an explanation of the science, read the book.
The book gives some intriguing hints about our past, and what follows is my guessing: Modern humans developed roughly 100,000 to 200,000 years ago in Africa. They were doing okay until a catastrophe occurred, the eruption of the Toba volcano in Sumatra around 73,000 years ago, +/- 4000 years. Toba was so big it had a massive effect on life on earth, even in Africa. Humans died off so only perhaps a couple thousand survived. It turned out the survivors were smarter than average, ready to make the most of their environment when a better climate returned.
65,000 years ago humans were hunter-gatherers. They had two "economic systems" for getting food. One was on the savannah, hunting on the grasslands. The other was collecting seafood on the ocean shore. 60,000 years ago, give or take, the seafood gatherers followed the shoreline from the horn of Africa across Arabia, India, etc. all the way to Australia. People have been in Australia a long time, 50,000 years give or take.
The grassland hunters stayed in Africa until climate change made the Sahara grassy, then some of them moved north and east, out of Africa across Sinai. This was about 40,000 years ago. They occupied all the grassland available, which took them well into central Asia perhaps as far as Mongolia. There were also grasslands in Europe and they moved west. The story of how long they stayed in central Asia before moving into China and Europe is not covered in the book. Climate may have forced them to stay in central Asia for thousands of years, but to retreat to higher ground to find sufficient water. In due course they spread out from central Asia, peopling Europe and mixing with descendants of the seafood gatherers as they moved east and south throughout Asia.
This book was written only two years into the project. Now in 2010 there is a lot more data available. I hope the author publishes more results of the genographic project soon.
Posted by rob at May 21, 2010 07:54 AM
Comments
Posted by: Anonymous at May 21, 2010 07:54 AM