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Who was the human Mew?

If you’re getting back into Pokémon Go thanks to the new game announcements, you’re probably hot on the trail of the Mythical Pokémon known as Mew. The game’s new Special Research feature lets you track down the powerful (and powerfully pink) Pokémon. Along the way, you learn that Mew shares DNA with all known Pokémon; after all, it’s believed to be the “ancestor of all Pokémon.” But this idea of a common ancestor for the wide variety of Pokémon species isn’t just something that Nintendo, Game Freak, or Niantic came up with. It’s actually an important idea in evolutionary biology and genetics called the most recent common ancestor (MRCA).

 

Every one of us descends from the human Mew

As the name suggests, an MRCA is a biological ancestor that multiple organisms or species have in common. We can sometimes find evidence of MRCAs in the DNA of their descendants, and we can use that evidence to estimate how long ago those MRCAs lived. For recent MRCAs, doing this analysis can even help identify them. This kind of analysis enables features like the “Genius Results” in National Geographic’s Geno 2.0. At some point in the last 120,000 years, each of us has a MRCA with a historical figure like Queen Victoria or Genghis Khan; where we differ is when that MRCA lived. (We can only assume that this kind of analysis is how in-universe researchers like Professor Willow determined that Mew is the MRCA for the over 800 unique Pokémon!)
Human beings, as a species, have a general MRCA—our human Mew, if you will. Regardless of where in the world our recent ancestors came from, every one of us descends from the human Mew. But, because of genetic recombination in our autosomal DNA, some of us might not have inherited any DNA from them. So trying to study this MRCA is—like using a Water Gun on a Bulbasaur—not very effective. Some mathematical models estimate that this MRCA could have lived as recently as a few thousand years ago,1 but we can’t narrow this window much further by looking at our DNA.
Luckily, there are two other important human MRCAs that we can study. These are our matrilineal and patrilineal MRCAs, or our MRCAs exclusively on our maternal or paternal line. They’re commonly referred to as mitochondrial Eve (or mt-MRCA) and Y-chromosomal Adam (or Y-MRCA).

Mitochondrial Eve is the female that all humans alive today are descended from on their mother’s side. We trace human matrilineal ancestry through the DNA in our mitochondria. These “powerhouses” of our cells have a small part of our DNA that is separate from the rest of our genome. For various reasons, each of us only has mitochondrial DNA from our biological mother. Fortunately for genetic research, this phenomenon allows us to trace back anyone’s direct maternal line of descent. In doing so, scientists have discovered that these lines converge on mt-MRCA approximately 100,000 to 200,000 years ago.3–5 (Different studies have found different ranges, though they tend to fall in this window.)
Y-chromosomal Adam is the male version of mitochondrial Eve: This MRCA is the male that all humans alive today are descended from on their father’s side. But unlike with mitochondria, the Y chromosome is both inherited and passed on only by males. That direct father-to-son biological inheritance allows us to trace human patrilineal ancestry through the Y chromosome. Researchers have traced this ancestry back to estimate that Y-MRCA lived approximately 250,000 to 350,000 years ago.6–8
At a glance, it may seem odd that the estimated timeframe for Y-MRCA differs so much from that of mt-MRCA. But that difference points to a key fact about these two MRCAs: They need not have lived at the same time. Humans inherit mitochondrial DNA and Y chromosomes independently from one another, so the overall matrilineal and patrilineal lines are independent from each other as well.
Where those lines converge may also change as time goes on. That change will, in part, happen because our knowledge about our human MRCAs will improve over time. New breakthroughs and discoveries are always improving both how we study genetics and what we know about the distant past.
But our MRCAs may also change because we continue to evolve as a species. As we do, some mitochondrial or Y-chromosomal lineages may not survive. If a particularly old lineage doesn’t survive, a different ancestor may become our mt-MRCA or Y-MRCA. The current MRCAs would still be common ancestors for all humans, but they wouldn’t be the “most recent” anymore.
The same thing can happen for our general human MRCA as well, though it will be more difficult to know when. That’s unlikely to happen to the Pokémon MRCA Mew, since the only evolution happening with Pokémon nowadays is from weaker to stronger versions. So when you finally get to encounter it in Pokémon Go or the Pokémon Yellow reboots, the Pokédex will still recognize it as the MRCA.

 

1Rohde, Douglas L. T., et al. “Modelling the Recent Common Ancestry of All Living Humans.” Nature, no. 43, Sept. 2004, http://steveolson.com/uploads/2009/04/nature-common-ancestors2.pdf.
2“The Unmasking of Mitochondrial Eve.” Science, no. 238, 4823, Oct. 1987.
3Cann, Rebecca L., et al. “Mitochondrial DNA and Human Evolution.” Nature, no. 325, Jan. 1987, https://www.nature.com/articles/325031a0.
4Fu, Qiaomei et al. “A Revised Timescale for Human Evolution Based on Ancient Mitochondrial Genomes.” Current Biology, no. 23, 7, Mar. 2013, https://www.cell.com/current-biology/fulltext/S0960-9822(13)00215-7.
5Poznik, G. David, et al. “Sequencing Y Chromosomes Resolves Discrepancy in Time to Common Ancestor of Males Versus Females.” Science, American Association for the Advancement of Science, 2 Aug. 2013, science.sciencemag.org/content/341/6145/562.
6Mendez, Fernando L., et al. “An African American Paternal Lineage Adds an Extremely Ancient Root to the Human Y Chromosome Phylogenetic Tree.” The American Journal of Human Genetics, no. 92, 4, Apr. 2013, p. 637, https://www.sciencedirect.com/science/article/pii/S0002929713000736.
7Karmin, Monika et al. “A Recent Bottleneck of Y Chromosome Diversity Coincides with a Global Change in Culture.” Genome Research 25.4 (2015): 459–466. PMC. Web. 15 June 2018.
8Mendez, Fernando L., et al. “The Divergence of Neandertal and Modern Human Y Chromosomes.” The American Journal of Human Genetics, no. 98, 4, Apr. 2016, p. 728–734, https://www.cell.com/ajhg/fulltext/S0002-9297(16)30033-7.
9Glansdorff, Nicolas, Ying Xu, and Bernard Labedan. “The Last Universal Common Ancestor: Emergence, Constitution and Genetic Legacy of an Elusive Forerunner.” Biology Direct 3 (2008): 29. PMC. Web. 15 June 2018.
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Categories: DNA Stories