Human Common Ancestor Lived 3500 Years Ago

Nature Science Update reported on a surprising find by Joseph Change (Yale) and Douglas Rohde (MIT).  They claim, based on computer modeling of human breeding and migration, that we are all related to the same common ancestor, not millions, but just thousands of years ago, possibly just 1500 BC in Asia, and that perhaps a couple of thousand years before that, everyone alive at that time was an ancestor of all of us living today.  The results are published in Nature Sept. 30.¹
    The finding is not entirely new; it is more a refinement of simpler models taking better account of migration and geographical isolation.  It does not mean people didn’t exist before that, but only that the current population is genealogically related.  Jotun Hein (Oxford) cautions in the same issue² that genealogical questions are “distinct from questions about the history of our genetic material,” which are estimated by different methods: “Universal common ancestry (in the pedigree sense) and genetic common ancestry thus occur on different timescales,” he says.
    If you think about it, it’s not all that surprising that in relatively few generations, a population’s family trees will overlap.  Think of inverted pyramids that overlap slightly; as they grow (going back in time), they will all eventually converge, unless the populations are completely isolated, which does not seem to be the case for any people group.  Simple models that assumed random mating converged in just 33 generations, or 800 years ago, which is clearly unrealistic.  By taking geography and history into account, Hein says, Rohde has tried to arrive at a more credible date for the MRCA (most recent common ancestor).  Even more surprising, Hein says, the models predict that before the MRCA, anyone alive would have been an ancestor of everyone alive today.  Rohde, Olsen and Chang explain:

Given the remaining uncertainties about migration rates and real-world mating patterns, the date of the MRCA [most recent common ancestor] for everyone living today cannot be identified with great precision.  Nevertheless, our results suggest that the most recent common ancestor for the world’s current population lived in the relatively recent past–perhaps within the last few thousand years.  And a few thousand years before that, although we have received genetic material in markedly different proportions from the people alive at the time, the ancestors of everyone on the Earth today were exactly the same. (Emphasis added in all quotes.)

The implication is that the entire human race today, no matter the continent, culture, skin color, language or lifestyle, is a member of one big family:

Further work is needed to determine the effect of this common ancestry on patterns of genetic variation in structured populations.  But to the extent that ancestry is considered in genealogical rather than genetic terms, our findings suggest a remarkable proposition: no matter the languages we speak or the colour 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 laboured to build the Great Pyramid of Khufu.

For another summary, see the report on EurekAlert, “Most recent common ancestor of all humans surprisingly recent.”  Few other popular science news sources are reporting the story – not New Scientist, Scientific American, National Geographic, the BBC News or MSNBC – as eagerly as they typically do with discoveries of hominid fossils alleged to be human evolutionary ancestors.

¹Douglas L. T. Rohde, Steve Olson, and Joseph T. Chang, “Modelling the recent common ancestry of all living humans,” Nature 431, 562 – 566 (30 September 2004); doi:10.1038/nature02842.
²Jotun Hein, “Human evolution: Pedigrees for all humanity,” Nature 431, 518 – 519 (30 September 2004); doi:10.1038/431518a.

Notice the model converges on a few thousand years ago, not millions.  Such a date is closer to Noah than Lucy.  Care should be exercised interpreting what this means, because it is somewhat of a counterintuitive artifact of a mathematical model that makes certain assumptions.  Another counterintuitive result, Hein claims, is that “not many generations ago (about six), members of our pedigree existed that did not contribute to us genetically.”  The authors are not claiming that humankind popped into existence a few thousand years ago, but only that everyone alive today had the same ancestors.  Can the same models be applied to guppies, tigers and oak trees?  Hein points to additional interesting questions that will require further refinement of models and the combining of pedigree and genetic ancestry information.  One question he asks is, “In the idealized models, how far back would one have to go to find a single couple who are the lone ancestors of everybody?” to which we might add, “and did their names start with A and E?”
    We can’t judge how valid is Professor Rohdes’ computer model, but it is interesting that this was not published by Answers in Genesis, but by Nature and by researchers from MIT and Yale – not institutions particularly interested in validating Biblical chronology.  It calls into question evolutionary assumptions about human pedigrees stretching back tens of thousands and hundreds of thousands of years.  It also means that all those “racial” differences between people are superficial and must be of recent origin.  Like AIG has emphasized in its Biblical creationist answer to racism, we truly are of “one blood,” just as Paul told the Greek philosophers on Mars Hill (Acts 17).