With their new article for the journal BIO-Complexity, University of Stockholm mathematician Ola Hössjer and Discovery Institute biologist Ann Gauger have set the standard for considering the question of a “first couple” in light of population genetics. Obviously, the possibility that human beings can all trace our ancestry back to such a pair would have profound implications. It’s why atheists like Jerry Coyne sought to bulldoze religious believers on the subject, with much success.
As recently as 2011, Coyne could write:
[T]here’s one bedrock of Abrahamic faith that is eminently testable by science: the claim that all humans descend from a single created pair — Adam and Eve — and that these individuals were not australopithecines or apelike ancestors, but humans in the modern sense. Absent their existence, the whole story of human sin and redemption falls to pieces.
Grant Him the Point
I’m not sure it is a “bedrock of Abrahamic faith,” for me at least, but let’s grant him the point. From “Adam and Eve: the ultimate standoff between science and faith (and a contest!)”:
Unfortunately, the scientific evidence shows that Adam and Eve could not have existed, at least in the way they’re portrayed in the Bible. Genetic data show no evidence of any human bottleneck as small as two people: there are simply too many different kinds of genes around for that to be true. There may have been a couple of “bottlenecks” (reduced population sizes) in the history of our species, but the smallest one not involving recent colonization is a bottleneck of roughly 10,000-15,000 individuals that occurred between 50,000 and 100,000 years ago. That’s as small a population as our ancestors had, and — note — it’s not two individuals. [Emphasis added.]
He was dancing a jig in response to an article in Christianity Today that seemed to prepare the way for a retreat on some hefty theological issues. As Ronald N. Ostling wrote there:
So is the Adam and Eve question destined to become a groundbreaking science-and-Scripture dispute, a 21st-century equivalent of the once disturbing proof that the Earth orbits the sun? The potential is certainly there: the emerging science could be seen to challenge not only what Genesis records about the creation of humanity but the species’s unique status as bearing the “image of God,” Christian doctrine on original sin and the Fall, the genealogy of Jesus in the Gospel of Luke, and, perhaps most significantly, Paul’s teaching that links the historical Adam with redemption through Christ (Rom.5:12-19; 1 Cor.15:20-23; and his speech in Acts 17.
A Comparison with Heliocentrism
Biologist and theistic evolution proponent Dennis Venema, then of BioLogos, would later follow up with his book Adam and the Genome. He adopted the same comparison of believing in a historical founding couple with denying that our planet goes round the sun: “The sun is at the center of our solar system, humans evolved, and we evolved as a population.”
Hössjer and Gauger realized that assertions like this had not been properly tested. Their own scrupulous work on the relevant data found that Coyne and others, in bullying Christians and Jews on how “we can dismiss a physical Adam and Eve with near scientific certainty,” were in reality poorly supported by the “scientific facts” they claimed to have securely on their side. From “A Single-Couple Human Origin Is Possible”:
Using a previously published backwards simulation method and some newly developed and faster algorithms, we run our single-couple origin model of humanity and compare the results to allele frequency spectra and linkage disequilibrium statistics from current genetic data. We show that a single-couple origin of humanity as recent as 500kya is consistent with data.
Read their article. The science behind their model and how they tested it is important, but for the layman, it may need some translation. In an interview with Justin Taylor, Dr. Hössjer and Dr. Gauger oblige us:
AG: The science as we know it shows that it is mathematically possible for us to have come from just one man and one woman. That is based on population genetics, a field that keeps track of genetic diversity in populations over time.
We say it is possible, not proven, because there are many other things to deal with, like the fossil record.
OH: Yes, this is correct. It is hard to prove that a certain model of human history is the right one based on genetic data from individuals of today. The reason is that sometimes quite different models of human ancestry might fit genetic data equally well.
We showed that a model with a first unique couple gave a good fit to some African genetic data. Therefore we cannot rule out a model where humanity started from a first couple in favor of a model where we share ancestry with chimps and other species.
Despite these difficulties of inferring human history, it might be possible though in the future to favor one model over the other, when more data sets are analyzed and more complex models are fitted…
OH: Genetic data is like fingerprints. Any individual (except monozygotic twins) has a unique DNA that identifies him or her. The more related two different individuals are, the more similar their genetic data is.
Human history is like a genealogical tree that connects all individuals alive today. The first human couple forms the root of the tree, whereas individuals of the present form the tips of the tree.
It is possible to infer a tree of human ancestry (with quite a lot of uncertainty) by trying to fit various trees and investigate which of these trees that are most consistent with genetic data. The inferred tree should be able to pick up that pairs of individuals with more similar DNA are more closely related. That is, pairs of individuals with more similar DNA should have ancestral lineages that merge more quickly, so that their most recent common ancestor lived more recently.
To complicate things: A genealogical tree is not the same thing as a pedigree. A pedigree gives parental relationships, whereas a genealogical tree shows how DNA is inherited. Each individual has a unique pedigree but many different genealogical trees. The reason is that genes from different chromosomes are inherited in different ways.
AG: Think of it like solving a puzzle. You have current mutations as clues, and you know who has those mutations. If you are lucky, you also know something about whether those people are related. So you work your way backward in time so that the mutations make sense, arising in person A1, then passing to person A2 and B1, then B2, then B3 in the present.
Massive computational models do it for the whole genome and go back potentially millions of years. It’s a best-fit model, not a guaranteed “this is the way it was on Saturday, April 15, 200,001 BC” kind of thing.
Permitted, Not Disallowed
[A]lthough the dates of genetic common ancestors (which of course differ for nearly all of our genes, since they recombined in the past with other genes and “coalesced” at different times) can be tested, and it can be shown that there was no pair of contemporaneous humans that gave all of us our genetic legacy, the genealogical A&E has the convenient advantage of being untestable. [Emphasis in the original.]
Oh, really? That was just 10 days before Hössjer and Gauger released their study.
A first couple is permitted by science, not disallowed by it. Going forward, anyone writing on the subject needs to have weighed the testing work of Hössjer and Gauger presented in their article. Venema, under pressure from the “scientific facts,” ultimately conceded the point, to his credit. (See, “Discussion Over: On Adam and the Genome, Former BioLogos Fellow Backs Down.”) Not so, as far as I’m aware, Jerry Coyne.
Photo credit: pasja1000, via Pixabay.