Theology, philosophy, math, science, and random other things

Evidence for a historical Adam and Eve

I previously posted a new interpretation of the Genesis creation story, which I believe to be absolutely groundbreaking. It's backed up by a good amount of scientific research, and the consensus of multiple other thinkers. That post was aimed more at Christians, in detailing how we should interpret the Bible in light of all the new evidence. This post will be aimed more generally, at anyone who has questions about the historical existence of Adam and Eve. How should you react to the new evidence? How should you update your beliefs?

Here is my claim: the scientific contents of my interpretation is a major piece of evidence for the veracity of the biblical account of Adam and Eve, and for Christianity as a whole. In other words, I’m not settling for mere “compatibility” with the known sciences; what we have here is actual, strong, positive evidence, and you need to adjust their beliefs accordingly.

The problem with such a claim is that people generally don't have a nuanced view of evidence. This often leads to poor discussions, because without nuance, every claim of “evidence” gets conflated with “truth”, and since we can’t allow that, every field - indeed, every person - develops their own siloed and tribalistic notion of what counts as “real evidence”. This is why the most frequent counter-claim to evidence is to simply shout “that’s not evidence!", for failure to meet some esoteric, ad-hoc definition that only exists in the mind of the shouter.

We can avoid this mess, and restore nuance, by adopting the Bayesian definition of evidence. This post, then, will largely be a Bayesian argument, providing new evidence for the historical existence of the biblical Adam and Eve. As such, some degree of familiarity with Bayesian thinking will be required. If you're not well versed in this area, I urge you to read the following posts as a starting point:

Now, to begin, what are the scientific contents of my new interpretation? Here's a partial summary:

  • A 2004 paper in Nature, titled "Modelling the recent common ancestry of all living humans", showed that the most common recent ancestor of all humans alive today would have lived only a couple thousand years ago.
  • Joshua Swamidass, in his book "the Genealogical Adam and Eve", showed that this number doesn't change much even if we change "all humans alive today" to "all humans alive at the time of Jesus".
  • Furthermore, such estimates are incredibly robust: even aside from the MOST recent common ancestor, virtually anyone living just a little bit beforehand can be the ancestor to the required population. This also means that the actual genes from any one such ancestor or couple would be effectively undetectable, due to dilution in the larger population.
  • Numerous possible objections to such universal ancestry - like the supposed isolation of the population of the Americas or the Andaman islands - have been satisfactorily resolved. Humanity really is descended from a couple from just a few thousand years ago. Furthermore, such a couple doesn't even need to be all that special; there are innumerable such couples, who are ancestors to us all.
  • The obvious implication here is that the biblical Adam and Eve was just such a couple. This, incidentally, completely removes the issue of "incompatibility" between the Genesis creation account and evolution, with minimal restrictions on how we interpret Genesis.

This, then, introduces the first way in which the above set of facts serves as evidence for a biblical Adam and Eve: by removing a previously strong piece of evidence against them. Before I developed my interpretation, I would have said that the theory of evolution is a very strong argument against the historical existence of Adam and Eve. This now needs to be retracted, and this retraction will, of course, have the effect of a strong piece of evidence FOR Adam and Eve.

The second way in which these facts serve as evidence is through a straightforward application of Bayes' rule: Some fact E is evidence for a hypothesis H, if H explains E better than its rivals. In our case,

  • H is the historical existence of the biblical Adam and Eve.
  • ~H is its rival: the non-existence of the biblical Adam and Eve, which says that they were merely fairy tales or allegorical figures.
  • E is the set of facts I mentioned above. In particular, I will be focusing on one subset - the shocking recency of the common ancestor, who only lived several thousand years ago.

And it turns out that the existence of Adam and Eve (H) does a FAR better job of explaining the above facts (E) - in particular, the shocking recency of the common ancestor - compared to the rival hypothesis (~H). That is to to say, P(E|H) >> P(E|~H).

Let's look at each of those probabilities. How well does Adam and Eve (H) explain the recency of the common ancestor? Consider a poor, pious grandma who's ignorant of science and just wants to believe the Bible. For her, this recency is not at all surprising. It's completely expected. “Of course humans have a common ancestor in the last several thousands years”, she would say, even after handicapping herself by not including any science. In terms of probabilities, that translates to P(E|H) ~ 1.

But what if you're a fully trained evolutionary biologist, who thought that Adam and Eve were just a fairy tale (~H)? How would you have reacted? Well, we don’t have to wonder: we have a useful iconic figure in Richard Dawkins, who wrote in “The Ancestor’s Tale” that “I find these calculated dates astonishingly recent”, when he learned of the recency of the common ancestor (E). That is, P(E|~H) << 1.

Nor is Dawkins alone in that assessment. The Wikipedia article on MRCA says:
"…Joseph T. Chang, Douglas Rohde and Steve Olson calculated that the MRCA lived remarkably recently…"

And these authors, in the very paper in Nature that form the immediate basis for E, says:
"...the genealogies of all living humans overlap in remarkable ways in the recent past . In particular, the MRCA of all present-day humans lived just a few thousand years ago..."

Joseph Chang says in his 1999 paper that:
"...all of present-day humanity may have a common ancestor who lived as little as 100 000 years ago , a time that seems to many to be surprisingly recent". Note that he's talking about the Mitochondrial Eve here, and even a date of 100 000 years is considered surprisingly recent!

And in the same paper:
“…if the logarithmic time to CAs seems patently implausible, then…”. Here he’s talking about an estimate of ~500 years.

While we can quantify this further, the adjectives here are quite sufficient. The recency of the common ancestor (E) is "astonishing", "remarkable", "surprisingly recent", almost "patently implausible". These strong and unanimous reactions leave no doubt that P(E|~H) << 1. Doubly so, given that these quotes come from an iconic atheist and evolutionary biologist (Dawkins), the authors who made the very discovery that we're talking about (Chang, Rohde, Olson), and well-respected organizations (Wikipedia, Nature).

The rest of the argument is merely a matter of assembling the probabilities according to Bayes' rule. P(E|H) ~ 1, and P(E|~H) << 1. Therefore the Bayes factor of E toward H is >> 1. That is, E is a strong piece of evidence for H. The recency of the common ancestor is a "remarkable", "astonishing", and "surprising" amount of evidence for the historical existence of the Biblical Adam and Eve.

At this point, it's important to remember the nuance behind the Bayesian definition of evidence. Evidence is probabilistic. It is not confirmation. It is not proof. You can have strong or weak evidence for or against a likely or a ridiculous hypothesis, and you take all that into consideration to come to your conclusion. In fact, I gave an example of this earlier, when I said that before I developed my interpretation, I considered evolution to be a strong piece of evidence against Adam and Eve, and against Christianity as a whole. But even back then, I was a Christian and did not have any real doubts about the fundamentals of the faith.

So you don't have to necessarily affirm that the Biblical Adam and Eve existed. You may have thought that the hypothesis was far too unlikely to begin with, so that it can’t be confirmed even with an “astonishing” amount of evidence. You may choose to disregard the scientific consensus that says that P(E|~H) << 1. You may have never thought that evolution was an issue for Adam and Eve, or you might have secretly, somehow believed in a recent common ancestor independently. Fair enough. Bayesian thinking allows for some degree of subjectivity.

But for a huge portion of people who are interested in this topic - those who are willing to listen to scientists, and are engaged in the "science and religion" conversations - the above evidence is strong. You need to adjust your beliefs accordingly.

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