Mitochondrial Eve

You thought we carried genes from both our parents, right? That’s only partially true. As most of us know, we have 23 pairs of chromosomes that are indeed the mix of genes from both our parents. Apart from that, as Siddhartha Mukherjee explains in his masterpiece, The Gene, there’s also the mitochondria within which each cell that has its own set of genes that has nothing in common with the rest of our genes! Further, the genes of the mitochondria come only from the mother.

Now consider the full implication of this. Or if you can’t, let Mukherjee explain it for you. The genes in your mitochondria are identical to those in your mother, who in turn got them from her mother and so on… it’s only women all the way up the mitochondrial chain. Or to put it differently, a male is a dead end as far as the transmission of the mitochondria gene set is concerned.

Now comes the best part: A world-wide survey (across races and countries) of the human mitochondrial DNA in 1987 yielded a surprising result:
“All mitochondrial DNAs stem from one woman.”
Yes, you heard that right: every single living human can trace their mitochondrial DNA back to a single woman. As Mukherjee writes:
“In human genetics, she is known by a beautiful name – Mitochondrial Eve.”

This sounds unbelievable, but it’s true. But it’s also very easy to misunderstand. It does not mean that all humans can trace their origin back to a single woman. Remember, this only means that all living humans today have the same genes in our mitochondria. But why is that different from saying that we share a “common mother”?

The pic below explains the point:
-         Squares indicate males, a dead end for the transmission of the genes of the mitochondria.
-     Circles indicate females, who can potentially transmit the genes of the mitochondria. But obviously, some daughters may die before having children.
-     The colors indicate different women at the “origin”, each with her own set of genes of the mitochondria. Note the many colors, indicating many “mothers” at the origin.
-      Over time, as Mukherjee says, it’s just maths:
      “If the founding population of a species is small enough, and if enough time has passed, the number of surviving maternal lineages will keep shrinking… until only a few are left… For modern humans, that number has reached one.”


And that’s why that one woman isn’t called Eve, but Mitochondrial Eve.

Comments

  1. Ramiah KumarOctober 30, 2016 at 11:36 AM

    You have re-elaborated the argument presented by Siddhartha Mukherjee. His book is good and I liked his sense of humor in particular! Only when you and I discussed I understood that science has traced our common ancestor along the mothers' line, the Mitochondrial Eve. I had wrongly assumed that she was the common ancestor, somewhat like the Eve of the Bible, but traced along scientific methods ignoring the Bible of course!

    This Mitochondria is a bugbear for me. What I understand is that it is something of a benign parasite residing within our cells. They say the parallel is something of the chlorophyll as cell in the Plant Kingdom, which is a benign parasite that was instrumental in building the great kingdom itself.

    Even after stripping all the technical jargon, I am still at sea, as far as biology goes! Physics and maths, along with Vedanta with your permission, are my cups of tea not other subjects - particularly biology. That apart, I am happy to know that there are dead ends and knowledge barriers in biology too. We can't know everything, for sure. I hope one day a Heisenberg (physics) cum Godel (maths) will appear in biology too, and formally establish something along the lines, "knowledge has to have its foundation on uncertainties (in physics) and the need for limitlessness of axioms plus the finality that always proof may not exist (maths)".

    Even without someone declaring that kind of thing, I already feel convinced that is the case, now that I am reading "The Vital Question - why is Life the Way it is" by Nick Lane, who discusses unsettled and unresolved challenges that scientists face. I hope Nick means "why is life the way it is, i.e. like maths and physics with un-knowability as part and parcel of it at core level?!" :-)

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