Saturday, August 20, 2011

Ancestors: Who's your great great great great grandpappy?

Race, ethnicity, culture, family...all important to people. But usually we think of these things completely separate from reality.

I have been reading several books that together have put some of this into perspective. Each of us are part of the whole sweep of human evolution, and we are all related in a very real, genetic way.

This man might be your ancestor:

(Ramesses II, king of Egypt, 13th century BC)

Yep, I bet lots of people today could, if only we had all the information, trace their ancestry back to this man. I would guess somewhere in the millions of people today are his descendants.

Go back far enough and we are all related. This is a fact. Or, more precisely, every little piece of our DNA ultimately derives from a common ancestor that can be traced back to some specific time and place.

This has most accurately and famously been done with our mitochondrial DNA. This DNA is something we all get from our mothers, so it is a strictly maternal descent. Men contribute nothing to it. In 1987 an amazing paper in the Journal Nature presented an analysis of modern mitochondrial DNA to show that all human beings can trace their mitochondrial DNA back to a common ancestor living in East Africa some 100-150,000 years ago. At that time some 20,000 anatomically modern humans were around.

Interestingly, studying mitochondrial DNA of modern humans indicates that African Bushmen have some of the oldest patterns of mitochondrial DNA around. The rest of us moved away and lost some of the mitochondrial diversity that was maintained in the Bushmen. It is probable that the divergence of the ancestors of the Bushmen and the ancestors of the African Pygmies may be the very first ethnic division in human history since we first started diversifying after mitochondrial Eve. Note: both names are considered derogatory, but no other good generic names are available...Bushman and "Forest People" are considered somewhat preferable because they imply a connection to the environment these people have lived in for millennia, but Bushman and Pygmies are the commonly known terms.

A similar analysis using modern Y-chromosomal DNA (traced only through the male lineage) showed that all men alive today can be traced back to a common grandpappy in East Africa some 60-90,000 years ago. Yep...Richard Simmons and Mr. T are both descendants of the same man.

Truth is, you can do the same kind of analysis with ANY piece of DNA in the just is much harder to do than with the mitochondrial or Y-chromosomal DNA. But statistical analyses have shown that all of us can trace our DNA molecular patterns back to some 86,000 common ancestors. Those roughly 86,000 people, from different places and different times (though mostly probably from Africa since that is the place of our common descent) are our shared genetic heritage.

These are great numbers and indicate how closely related we all are. But once humans started moving out of Africa, that common genetic heritage diversified. We started splitting into ethnic and cultural groups, and possibly even started evolving apart at one point. It has often been assumed that humans have been evolving slowly since modern humans (Homo sapiens) first evolved around 150,000-200,0000 years ago, plus or minus some tens of thousands of years. Interestingly, this places the mitochondrial eve near our evolutionary origin...probably some tens of thousands of years after we became anatomically modern Homo sapiens. But the humans of 150,000 years ago weren't quite what we are today. Physically they would pass. But culturally, and presumably in terms of how the brain worked, was different. Stone tools made from our earliest tool using ancestors, Homo habilis, some 2.4 million years ago up to even Homo sapiens, tended to be slow to change and tended to be similar over wide areas. This doesn't mean things stayed the same throughout that period. Far, far from it. Over nearly 2.4 million years things changed a lot, but the pace of that change was slow and regional variation was small. Then starting sometime around 50,000 years ago, well after we physically evolved, something changed. Suddenly there were many more innovations in tools and far more regional variations. Complex culture seemed to suddenly evolve. Art started to evolve, culminating in the Cro Mangon culture art of Alta Mira and Lascaux. (As an aside, one theory, though one I consider shaky so far, is that the modern Basque are fairly direct descendants of this Cro Magnon culture...there is some genetic evidence for this, but...). Some kind of goddess or fertility cult seemed to start to appear, with widespread appearance of carved female figures called Venus figures. And people started spreading out over the globe. To me it seems like we suddenly evolved imagination starting around 50,000 years ago. Was it a change in our brain structure? Was it a breakthrough in language? No one knows.

Humans of other species (Homo erectus, Neanderthals) had left Africa before then. But they didn't contribute to our modern genes as far as anyone can tell. There is still a chance that some tiny part of our genetic ancestry is from Neanderthals or Homo erectus, but so far there is not one shred of evidence to support that. And we have isolated some Neanderthal DNA to use to try and look for common DNA patterns.

Evolution is driven by two things: population size (since the larger the population the greater the genetic diversity) and distance (since larger population distribution allows greater divergence). It used to be thought that once we evolved to be Homo sapiens we largely stopped evolving. Recent data shows this isn't true. It seems that around 5000 years ago human evolution, because it had reached a critical size and large distribution over most of the globe, suddenly sped up. We can't tell if we are diverging more than ever now, or once again, perhaps due to the bridging of those large distances through modern transportation, we are evolving slowly. The techniques used can't see events closer than, say, 5000 years ago. I suspect that as empires grew, steppe nomads swept across continents, and transportation improved, genetic exchanges increased across our entire population, more or less, to counter act the speed up in human evolution. However, some pockets of people in places like Australia and New Guinea would have been largely genetically isolated for millennia up until around the 18th century. So perhaps any slow down in the pace of human evolution would only have started a few hundred years ago. This means that for our early existence, from 150,000 to 5000 years ago, population size was small enough and our global distribution narrow enough, at least early on, that we were evolving slowly. Things sped up 5000 years ago, but my guess is slowed back down once sailing ships started reaching every corner of the world.

Then we come to a level of ancestry that most of us can understand: can we trace specific ancestors. Truth is, even fairly recently, a recent as a few thousand years ago, we can all trace our ancestry back to a fairly small population. In fact, in rare cases, large chunks of the modern population can trace to specific famous people. For example, Ramesses II was Pharaoh of Egypt in the 13th century BC. He was the greatest, most powerful king of Egypt ever. And Egypt controlled a wide empire. Ramesses II drew wives and concubines from all over: the Sudan area, Egypt, the Middle East. Maybe even from Greece and Turkey. He had more than 50 recorded sons and more than 50 recorded daughters, and this probably doesn't count children sired on slaves or through affairs. His children and grandchildren filled the top ranks of the nobility, military, diplomatic corps and priesthood. Further out, many of his great great grandchildren may have settled outside Egypt as soldiers, traders, scribes, etc. Some think almost every native born Pharaoh of Egypt after Ramesses II probably could trace their ancestry SOMEHOW back to Ramesses II. I would go further. I would say a significant chunk of people living around the Mediterranean today just might have a piece of DNA that can be traced back to Ramesses II. Perhaps even those Jews who supposedly left Egypt during Ramesses II's reign may just have had some people who "knew" an son of Ramesses II.

There is one case where this kind of connection is just about proven. DNA analysis has shown that 0.5 percent of the male population in the world, or roughly 16 million people, are direct male descendants of Genghis Khan. In essence a Y chromosomal pattern (hence only traceable through the male line) was found in this percentage of the population, mainly in the vast area conquered by the Mongols (from Russia to Korea), which could be traced back to the area of Mongolia at the right time in the 13th century. SOMEONE at that time and place who had many children and grandchildren is the ancestor of 16 million modern men. The person known to fit this profile is none other than Genghis Khan. This doesn't really PROVE Genghis Khan was the ancestor of all these people, but it strongly suggests it. He had many children and grandchildren who spread through the bulk of Eurasia and were very powerful for a long period of time. They raped and married and had large families. It is virtually certain that this really does place Genghis Khan as the direct ancestor of 0.5 percent of the male population in the world.

There are almost certainly many other prolific and powerful individuals who have contributed significantly to the modern gene pool. There is no way to know if Ramesses II is one of them because it is much harder to trace back that far with as much certainty as tracing back to the 13th century. But a similar analysis COULD be done to find if a similar chunk of modern humans can trace back to someone in the area of Egypt in the 13th Century BC. But Ramesses II probably fits the profile almost as well as Genghis Khan. Many people who derive from the Sudan, Egypt, Libya and the Middle East have pieces of DNA that came from Ramesses II.

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1 comment:

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