One of the big revelations of the RTB-PS workshop on human origins was @AJRoberts’s speculation on “mosaic eve.” Of course, this has an interesting history in the conversation, tracing some history back to Jerry Coyne (Jerry Coyne's Adam and Eve Contest).
Starting from our first principles, we set presuppositions about human population genetics that may be tested for consistency with evidence within scientific analyses, including population genetics.
In my previous blog, I referenced a presentation by S. Joshua Swamidass that helped clarify how others have misrepresented the human population genetics data in order to rule out the possibility of a sole progenitor pair. In scientific terms, they have ruled out a population bottleneck (of two) prior to roughly 500 kya. Another paper (published the same day as Swamidass’s presentation) by Ola Hössjer and Ann Gauger draws parallel conclusions to Swamidass based on different analyses.1
Swamidass’s analyses are based on calculations for the most recent date that four differing alleles could give rise to the extant human population. This date is indicated as TMR4A (time to most recent 4 alleles), in contrast to TMRCA (time to most recent common ancestor, which constrains diversity to only one allele). TMR4A indicates a timepoint, any time before which Adam and Eve might have existed and is a valid starting point for modeling population diversity from a presupposition that Adam and Eve were either a genealogical common ancestor to all extant humanity or a de novo created couple at the base of the human population, as Hössjer and Gauger point out. However, TMR4A is not an uncontested starting point for such population modeling from strict evolutionary perspectives.
Yet as Swamidass, Hössjer, Gauger, and others have suggested, it is reasonable to hypothesize that a de novo created couple need not be homozygous or clonal with respect to their genetic sequences. Since each reproductive pair potentially provides four alleles to the gene pool, it’s no stretch to hypothesize TMR4A for a founding couple. This is an especially reasonable hypothesis if a Creator intended them to establish a diverse human population.
One might argue that surely four alleles isn’t enough diversity for a population just getting started in regard to future survival or adaptive capacity. Wouldn’t such limited genetic diversity leave the future of the human race in a precarious position at its onset, even if the founding pair reproduced prolifically (say 20–30 offspring)? Perhaps this is why some people are more comfortable with the claim that the human population never dipped below thousands. From a different perspective, in regard to a creation model, limiting the cleverness and foresight of a Creator to an initial diversity of just four alleles in a founding couple doesn’t take into account the Creator’s creativity.
Certainly, if God intended an entire human population to arise from a de novo pair, and if no other source of human genetic diversity is allowed (because ours is a sole-progenitor pair model)2, then it is extremely reasonable to hypothesize that God created the first pair to provide and produce the desired diversity.3 If we concede that God could create with purposeful intent to populate all humanity from a founding pair, then TMR4A is reasonable, but perhaps not sufficiently diverse.