TMRCA of all living humans
Estimating time to MRCA of all humans based on the common genealogical usage of the term 'ancestor' is much harder and less accurate compared to estimates of Patrilineal and matrilineal MRCAs. Researches must trace ancestry along both female and male parental lines, and rely on historical and archaeological records.
Depending on the survival of isolated lineages without admixture from modern migrations and taking into account long-isolated peoples, such as historical societies in central Africa, Australia and remote islands in the South Pacific, the human MRCA was generally assumed to have lived in the Upper Paleolithic period. With the advent of mathematical models and computer simulations, researchers now find that the MRCA of all humans lived remarkably recently, between 2,000 and 4,000 years ago.
Rohde, Olson and Chang (2004) constructed a mathematical model that considered the tendency of individuals to choose mates from the same group, as well as the relative geographical isolation of such groups. The mathematical model with one particular set of parameters showed that the MRCA lived about the year 300 BC and yielded an identical ancestor point (IAP) of 3,000 BC.
The same 2004 Rohde paper also presented results from a computer program based on Monte Carlo simulation designed to overcome some of the limits of the mathematical model. The program took into consideration realistic population substructure and migration patterns, allowing the researchers to simulate historical human demography. A conservative simulation yielded a mean MRCA date of 1,415 BC and a mean IA date of 5,353 BC. A less conservative simulation gave an MRCA date of AD 55 and an IA date of 2,158 BC.
An explanation of this recent MRCA date is that, while humanity's MRCA was indeed a Paleolithic individual up to early modern times, the European explorers of the 16th and 17th centuries would have fathered enough offspring so that some "mainland" ancestry by today pervades remote habitats. The possibility remains that an isolated population with no recent "mainland" admixture persists somewhere, which would immediately push back the date of humanity's MRCA by many millennia. While simulations help estimate probabilities, the question can be resolved only by genetically testing every living human individual.
The paper suggests, "No matter the languages we speak or the color of our skin, we share ancestors who planted rice on the banks of the Yangtze, who first domesticated horses on the steppes of the Ukraine, who hunted giant sloths in the forests of North and South America, and who labored to build the Great Pyramid of Khufu".
An assumption that there are no isolated populations is questionable in view of the existence of various uncontacted peoples, who are suspected to have been isolated for many millennia, including the Sentinelese who have been isolated from the western world and also from the Asian mainland.
http://en.wikipedia.org/wiki/Mrca#TMRCA_of_all_living_humans (version de décembre 2011)
Une date aussi récente est pour le moins frappante. Notre ancêtre commun a vécu à l'époque historique, il était biologiquement identique à nous, parlait une ou plusieurs langues, était intégré à un groupe social, probablement au sein d'une civilisation majeure. Nous pouvons nous en sentir très proche.