Recent research on our common ancestors


I have been fascinated with the research on the most recent common ancestor (MRCA) of human beings ever since I read the research of Joseph Chang et. al. that suggested that that person could have lived as recently as about 50 CE or so, around the time of Jesus. (See here, here, and here for my previous posts on this topic.)

Chang was doing a statistical, not biological, analysis using a model of interbreeding where our MRCA could be traced back through any lineage but there is another way to do the tracking and that is by following just Y-chromosome only or the mitochondrial DNA only. Since the former is transmitted only through males, you would be finding the MRCA by going back through only the male lineage to reach the individual (dubbed ‘Y-chromosome Adam’) while the latter is transmitted only by females so you would be following only the female lineage and reach ‘mitochondrial Eve’. Naturally, the dates for the MRCA would get pushed back even further than a lineage in which the sex of the ancestors was ignored.

In Richard Dawkins’s book The Ancestor’s Tale (p. 52-55), he says that this ‘Adam’ would be expected to be around 60,000 years ago while ‘Eve’ would be around 140,000 years ago. But now more recent research using the sequencing of the DNA of the entire Y-chromosome suggests that Adam lived between 120,000 and 156,000 years ago and a similar analysis says that Eve lived between 99,000 and 148,000 years ago, contradicting the earlier idea that the Eve appeared earlier than Adam. Now they could have been contemporaneous.

The paper can be seen here and here is its abstract:

The Y chromosome and the mitochondrial genome have been used to estimate when the common patrilineal and matrilineal ancestors of humans lived. We sequenced the genomes of 69 males from nine populations, including two in which we find basal branches of the Y-chromosome tree. We identify ancient phylogenetic structure within African haplogroups and resolve a long-standing ambiguity deep within the tree. Applying equivalent methodologies to the Y chromosome and the mitochondrial genome, we estimate the time to the most recent common ancestor (TMRCA) of the Y chromosome to be 120 to 156 thousand years and the mitochondrial genome TMRCA to be 99 to 148 thousand years. Our findings suggest that, contrary to previous claims, male lineages do not coalesce significantly more recently than female lineages.

Of course, it should go without saying (but sadly needs to be said anyway) that this has nothing to do with the biblical story of Adam and Eve but those were merely the catchy names scientists gave to these ancestors. The fact that they existed earlier than 6,000 years ago will dampen the enthusiasm for biblical literalists but the fact that they may have existed contemporaneously may encourage those who think that while the Genesis story is a metaphor, it did represent reality in some way.

Comments

  1. AsqJames says

    We sequenced the genomes of 69 males from nine populations

    The details are way over my head, but to a layman that seems like an awfully small dataset from which to draw conclusions about all 7 billion genomes on the planet.

    @Reginald Selkirk,

    The margins of error overlap, so (assuming these estimates are correct), the two individuals could have been alive at the same time.

  2. left0ver1under says

    I wish anthropologists, biologists and other scientists would stop using religious claptrap terms for scientific discoveries.

    In epidemiology, the term for the first patient is “Index Case” or “Patient Zero”, the single point from where epidemic spread. If there is each a single common female and single common male ancestors, then perhaps they should be named the Zero Female and Zero Male.

  3. F [is for failure to emerge] says

    50 CE? Keep iterating new versions of assumptions, and get more data. From previous installments, I can see we’ve already backed out of the middle ages. Certainly, very few populations were totally isolated for long periods of time, but it seems like we’re missing still a great whacking chunk of statistics yet to be accounted for.

    Really, it sounds like the Ghengis Khan theory of modern human descent, or something out of a R. A. Wilson novel about Brian Boru or Charlemagne.

    Not to say I find the premise unreasonable at all, but the time frame vs. geographic distribution seems a bit off to me. Theoretically, Emperor Claudius could be the MRCA, for example? I know intuition is a bad guide, and humans innately have a poor grasp of probabilities (I am certainly no exception), but I think we are overlooking some constraints here.

  4. Lassi Hippeläinen says

    50 CE? How would the Amerindians fit into it? Anything younger than the end of Ice Age when Beringia was inundated seems suspicious. And the Autralian Aboriginees…

  5. Mano Singham says

    This is a tricky issue that they address here. The point is that few peoples were truly isolated. All it requires is for at least one person from a quasi-isolated group to intermarry with people from another area to create the necessary links. The most isolated were the Tasmanian aborigines.

  6. Lassi Hippeläinen says

    So they only have a model that hasn’t even been verified against measurements. Colour me doubtful.

    I’m more ready to believe the genetic analysis, because it is based on empirical evidence. But I also note that even if “Adam” and “Eve” lived at the same time, there’s no evidence that they ever met and had children.

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