We have all heard about Genghis Khan emperor conquered a vast territory and and established a huge empire. He had a reputation for genocide and also for his prolific fathering. Today the great khan has a total of 16 million Y chromosome descendants or 0.5% of all males globally. The size of the monument of the good Khan pictured above does indeed reflect his genetic contribution to the human gene pool.
This was the conclusion of a study described in the National Geographic. This is an extraordinary progeny. But these 16 million men carrying Genghis Khan’s Y chromosome does not even begin to describe demographics of his genetic heritage.
In fact the 16 million men who share Genghis Khan’s Y chromosome are only a tiny percentage of all the descendants of Genghis Khan. Simple arithmetic makes this clear.
I will assume the reader is male. If in fact you the reader is female then consider yourself a honorary male for the purposes of this thought experiment.
How many biological parents do you have? Two is the usual answer. I will use the notation 2^x. Two parents would be 2^1. Yourself are generation 0. There is just one of you or 2^0.
How parents have your Y chromosome? One of two, 1 in two or 1/2^1 at the -1 generation.
How many grandparents do you have? Four or 2^2. How many of your grandparents have your Y chromosome? One of four, or 1/2^2 at the -2 generation.
How many great grandparents do you have? Eight or 2^3. How many of your great grandparents have your Y chromosome? One of eight, or 1/2^3 at the -3 generation.
How many great great grandparents do you have? Sixteen or 2^4. How many of your great great grandparents have your Y chromosome? One of sixteen , or 1/2^4 at the -4 generation.
If we go back to the -10 generation we have 2^10 ancestors or 1,024 at that level. How many of these ancestors have your Y chromosome? 1/2^10. One of 1,024. Another way to look at this is to ask of all a man’s descendants at +10 generations into the future will have his Y chromosome? The is 1/2^10. About 1 in a thousand of his descendants at the +10 generation will have his Y chromosome.
The next question to ask how many generations have passed since Genghis Khan? It is not possible to know this. If 20 generations have passed then the total number of descendants including both Y chromosome descendants and non Y chromosome descendants alike will be 16 million multiplied by 10^20 or about one million. That is 16 trillion descendants at the +20 generation level. If 30 generations have passed then the total number increases to 16 quadrillion. 16,000,000 X 2^30 (1 billion).
These are impossible numbers and obviously many descendants of Genghis Khan have married many other descendants of Genghis Khan. These would not likely include Europeans or Africans. Large areas of Asia however would be descendants pretty well down to the last one. The 16 million Y chromosome descendants does not tell the whole story of the Khan’s legacy.
At this point the ancestor paradox becomes obvious. That is the number of ancestors increases exponentially with each generation back so that your number of ancestors exceeds the world’s population with fewer than 30 generations into the past. 2^30 is approximately 1 billion. The world’s population only exceeded 1 billion people in 1804. For someone like myself with English, Scottish, Cornish and Irish ancestry this really means I am descended from every reproducing person alive in Britain at the time of Edward I and probably most of Europe as well. This would include Edward I himself down to the lowest peasant. One and only one of these will be my Y chromosome ancestor.
Asian males living in the time of Genghis Khan would on average have hundreds of millions of descendants living today or perhaps billions but would have only between 10 to 20 Y chromosome descendants today.
The behaviour of Genghis Khan very anomalous indeed. The alpha male of all alpha males ever. “Kill all the men and rape all the women” certainly describes him. He killed about 10% of the world’s population at the time including half of the population of China. This is deeply biological behaviour turned up to ten. Maximising his genetic advantage. No animal in the wild would garner such an advantage on such a scale but humans can capitalise on simple technology to greatly magnify their natural mating advantages or perhaps even supplants natural disadvantages. In this way slightly dimorphic homo sapiens can exert a polygamous advantage like that of male elephant seals.
Social constructs can not alone explain this sort of behaviour. It is the genes of Genghis Khan which benefit from this behaviour and it is the genes which drives this behaviour. The Mongol Empire was an alpha male’s way of propagating his genes or more precisely the alpha male’s genes’ way of propagating themselves.
In Genghis Khan we see analogues of animal behaviour. This we can expect because homo sapiens are animals. Apes actually. We have have inherited our behaviour from evolutionary ancestors. We did not lose our biological inheritance at the neck up. A lion pride is a well known example of a polygamous species. Humans are not as polygamous as lions but in the record of the the great khan we do see an example which exceeds the norm for human males. With basic technology human alpha males have vastly exceeded what would be expected by the degree of dimorphism in humans.
A male lion pride owner has the job of propagating himself and protecting such progeny with his life if necessary. If his mating rights are overthrown by a younger stronger male lion the first job at hand is the killing or chasing away the old lion followed by killing his progeny in a very bloody affair. This is Genghis Khan, Jacob, David, Solomon and the sultans and emperors of various empires through history with their harems and frequently bloody successions. For the human alpha the animal behaviour is shielded probably even from the alpha male himself behind a lot nationalistic, moral ennobling or religious spin doctoring.
Examples like Genghis Khan illustrate the importance of biology in human biology and that is at odds with the social construct model of human behaviour. A Genghis Khan can not be socially constructed. A Genghis Khan is energised from deeper levels. The cerebral cortex does not create him as much as filter deeper instincts with some culture and a good justifying story for the expression of those instincts culturally shaped though they may be. We will realise darker angels of our nature in unexpected ways if we continue to deny the importance of the biological.