A statistical approach to MRCA

[Rohde, 2002] has run the first ever serious computer simulation of the history of the world's genealogy. He makes a serious attempt to model non-random mating. He sets up an abstract model of "continents", "countries" and "towns", which can be viewed not merely as geographic position but more abstractly as the pool from which one is more or less likely to choose a mate
- whether that pool be geographic, religious or whatever. He even simulates the historical growth of the world population - adjusting the birth and survival rate so that population growth matches the real numbers over the centuries from 1000 BC to 2000 AD. Interestingly, he found this made little difference to the MRCA date.

Given a reasonable choice of parameters, he estimates the MRCA for the world at c. 300 AD, with bounds of c. 150 BC to c. 800 AD. The lowest rate of migration (and hence lowest rate of cross-breeding) he tried was: probability of leaving the "country" 0.05 percent and probability of leaving the "continent" 0.001 percent. Even with this extreme local-breeding model he still gets an MRCA for the whole world in historical times at c. 150 BC.

Source : http://humphrysfamilytree.com/ca.math.html#computer.simulations

Before 700 AD, every single human is either ancestor of no one alive today, or ancestor of everyone alive today. [Rohde, 2002] refers to this as the "All Common Ancestors", or ACA, point. Obviously if someone in this period is a proven ancestor of someone alive today then they must be ancestor of everyone alive today. So, for example, Charlemagne, because he is a proven ancestor of some people alive today, is probably the ancestor of everyone alive today in the West. In fact, Chang's model predicts that around 80 percent of the population before the ACA point is an ancestor of everyone alive today (and 20 percent are ancestors of no one alive today).

Source : http://humphrysfamilytree.com/ca.math.html#rhode.simulations


Il est frappant d'imaginer que la plupart des individus qui ont vécu à l'époque antique, pour peu qu'ils aient assuré leur descendance aux premières générations, sont devenus des CA, des ancêtres communs à toute l'humanité, et qu'ils pourraient donc rétroactivement prétendre à juste titre être aujourd'hui une cause nécessaire (quoique évidemment non suffisante) de toute l'humanité.