The Ancestor's Tale

I recently finished Richard Dawkins’ The Ancestor's Tale. It is a readable opus on evolution back to the beginning of life. It looks at history backward; each species came from a certain past but there was no inevitability that any species would survive. Evolution is a story of who has survived and there were many possible ways the world could have been. The advantage of looking backward is that we can avoid the temptation to attribute to our ancestors any drive to progress or other teleological mechanism which suggests our destiny.

All apes share an geneological ancestor (concestor) who lived about 18 million years ago (18,000,000). All known life forms can be traced to a single ancestor (concestor) who lived more than 3 billion years ago (3,000,000,000). The continents were still joined together 150 million years ago. Human agriculture began about 10,000 years ago and human civilization (the Sumerians) about 7,000 years ago. I write the actual numbers because it is so hard for us to conceive geological time in its vastness. Tasmanian aboriginals, a form of homo sapien, were isolated from Australia about 13,000 years ago on the island of Tasmania, when land bridges were flooded by rising sea levels. This was the most recent isolation that lasted to modern times. They were discovered in about 1800 A.D., and exterminated by 1876 by agricultural settlers who viewed them as vermin.

What is the most recent common ancestor (MRCA) of all surviving humans today? It is quite clear that if we go sufficiently far back, everybody’s ancestors are shared. This makes geneology seem to me to be a bit parochial, although I have gotten sucked into the process at various times. Unfortunately, most of our family tree will remain unknown, so we need to estimate this by use of mathematics.

Assuming that population size is kept constant and mating is random, the surprising answer is only 12.3 generations ago. Assuming four generations per century, this is less than four centuries ago. It is even less if people reproduce younger than 25, which they probably did.

You can trace male genetic evolution through the Y chromosome and female genetic evolution through mitochondrial DNA. Once the last Tasmanian died, the most recent common ancestor of all of us alive today instantly jumped forward 10,000 years. By traveling up the tree father to father, the common male to all of us (Adam) dates back about 60,000 years while doing so mother-to-mother the common female (Eve) dates back 140,000 years. How can this be?

And here is another stunner: for particular genes, you are more closely related to some chimpanzees than to some humans.

Much of human knowledge defies “common sense,” or “conventional wisdom.” And I think these facts show that many of our moral or political stereotypes are based on very unscientific thinking. How can one claim a large division between races? Between religions? Between national identities? Between ourselves and other living creatures? It seems like you need to rely on some sort of creationism that marks humans or some kind of humans as a separate kind of thing. This is belied by DNA research and the fossil record. We share 98% of our DNA with chimpanzees. Get over it! You aren't that special.

That is just from the first 40 pages. Things get stranger and more interesting the further back you go.