Thursday, December 19, 2013

Revised evolutionary tree

Our knowledge of the human evolutionary tree has greatly improved, as DNA from fossils is decoded.   The New York Times reports that a complete Neanderthal genome was extracted from a 130,000 year old fossil toe.  That, along with other recent finds, gives this picture (picture and caption from Nature, via the NY Times):

A new study of ancient DNA indicates that modern humans branched off from ancestors of Neanderthals and Denisovans around 600,000 years ago. Later, interbreeding moved DNA between the branches. The percentages show how much DNA in a genome arrived through interbreeding. For example, people in Oceana have 3 to 6 percent Denisovan DNA.

Also, we might find out what distinguishes us, genetically speaking:
By comparing their high-quality ancient genomes to human genomes, Dr. Paabo and his colleagues are drawing up a list of mutations that are unique to our own lineage. “I would say it is a definitive list,” said Dr. Paabo. 

Dr. Paabo is intrigued by some mutations that affect genes involved in the development of the brain. But he sees the list as only a starting point for research. 

“What lies ahead is to understand which of these is important,” said Dr. Paabo. “That’s totally up in the air.”
Or, it might turn out that the story of the last few hundred thousand years of our evolution was cultural evolution, not genetic evolution.
The authors of the new study also compared the Neanderthal genome to modern human DNA to better understand what makes our own lineage unique. They have come up with a list of mutations that evolved in modern humans after their ancestors branched off from Neanderthals some 600,000 years ago.
The list of modern human things is quite short,” said John Hawks, a paleoanthropologist at the University of Wisconsin who was not involved in the study.
 Either this "list of modern human things" turns out to be to include some determinative things, or else, it is just mutations accumulated over time, not crucial to anything.  With luck, we will know soon enough.