Human origins

I have just read a fascinating book entitled, “The seven daughters of Eve,” by Bryan Sykes. This title is deceptively simple, it might alternatively have been entitled “Human population genetics by analysis of mitochondrial DNA.” While this wouldn’t have sold so many copies it would have been more accurate. Nevertheless the book is written in a very easy flowing style and is very explanatory and comprehensible.
Bryan Sykes is a Professor at Oxford University’s Insitute of Population Genetics and has pioneered the use of mitochondrial DNA (mDNA) as a means to follow human evolution.
This has enabled him to answer important and interesting questions such as how the Polynesians populated the Pacific Islands (did they come from Asia or from the Americas), were the bones discovered in a shallow grave near Ekaterinborg, Russia, those of the Romanovs and was Anastasia one of them, did homo sapiens displace earlier forms of humans (Neanderthals) or did they interbreed with them, and can one trace the lineages of Europeans, and by extension all the world’s populations, back to specific individuals.
First, in order to answer these questions we must understand what is mitochondrial DNA. Each cell of our body has within it many organelles, most significant of which are the mitochondria. These are the bodies responsible for respiration, the conversion of dissolved oxygen supplied by the blood into biochemical energy (ATP). Without mitochondria life itself would be almost impossible. These structures are not inherited via the usual mechanism of DNA recombination from sperm and ova that takes place in the fertilized egg. On the contrary they are inherited only from the mother in the cytoplasm that accompanies the egg.
Almost everybody knows that DNA is “deoxyribonucleic acid” and is the genetic substance, but the salient point about DNA is that it is found in the cell nucleus and it divides whenever a cell divides and then is reproduced to give two daughter cells, or it is carried by the sperm to the ovum where their respective DNAs combine. But, years ago a strange discovery was made, namely that mitochondria contain DNA of their own. This is a small relatively obscure packet that is responsible only for the reproduction of the mitochondria themselves. Since it is a small circular piece of double-stranded DNA it is though that it might have derived from a microorganism that has taken up permanent symbiotic residence in our cells.
Checking this small piece of DNA is a lot easier than the cellular DNA, and since it derives only from the maternal line, one can make conclusions about heredity. If two women or a woman and a man have identical sequences in their mDNA then they have the same mother, as simple as that. Since mutations occur in DNA (the exchangeof one base for another among the four A, T, C and G) over time (by chemical and other effects) so one can “measure” the time from one person to another by the number of mutations in their DNA. Thus the mDNA of a skeleton that is dug up can be compared to a contemporary human being, and the difference in their sequences can tell how old the skeleton is.
Because of lack of space, I will briefly answer the questions posed above: 1. The mDNA results conclusively prove that Polynesians came from SE Asia (Taiwan) and not from the Americas (as Thor Heyerdahl tried to prove with his Kon-Tiki expedition). 2. The skeletons found in a shallow grave near Ekaterinbourg were in fact the Romanovs, by comparison of their mDNA with that of living relatives, and Anastasia was not one of them! 3. Homo sapiens (also known as Cro-Magnon man in Europe) gradually replaced Neanderthals and other primitive men, there is no evidence of any inter-mixing. 4. By comparisons of sequences, Sykes was able to show that there are 7 common mDNA sequences in Europe that relate to 7 clan mothers. This shows that there is an undisturbed connection between ancient (65-17,000 years ago) and modern humans.
However, the distribution of these 7 founder sequences (a similar analysis can be done with male Y chromosome DNA) shows that there is no such thing as a “pure” race in Europe. By comparing to the whole world (not a complete analysis yet) it is possible to conclude that individuals moved across continents and huge distances and left their genetic mark in far places. One deduction from the results is that farming was intoduced gradually into Europe from the Middle East, and the indiginous hunter gatherers were not replaced but adapted to farming. The power of genetics!


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