Thursday, May 22, 2014

The population bottleneck

Even conservative Christians, it seems, have trouble believing that Adam and Eve were the literal ancestors of humanity.  That historicity has become increasingly problematic since the appearance of new papers in population genetics, showing that over the last few hundred thousand years, the population of Homo sapiens could not have been smaller than about 12,250 (10,000 who remained in Africa and 2,250 who migrated out of Africa to populate the rest of the globe). In other words, the human population never comprised only two people.
From what I've read, the population bottleneck is based on no fewer that five interrelated assumptions:
Specifically, she offers a critique of the claim that "there is too much genetic diversity to have passed through a bottleneck of just two individuals." Gauger lists five assumptions that undergird "the equations used to reconstruct these trees, and to calculate ancestral population sizes." These assumptions are:
  • Fixed population size.
  • No migration.
  • Random mating.
  • Constant mutation rates.
  • No selection.
To my knowledge, all five variables must line up in the right direction for the genetic argument against Gen 1-2 to go through. 
Keep in mind, too, that this presumes the uniformity of nature. Methodological naturalism. If, however, there's a "divine foot in the door," then that complicates the extrapolations. And, needless to say, Genesis doesn't view natural history as a closed-system. 


  1. Wouldn't that theory also go against Mitochondrial Eve?

  2. The argument must be geared to attack a perceived weakness that the arguer doesn't hold. Specifically:

    1) Darwinists should have no problem with new genetic information cropping up randomly.

    2) It's apparently inconsistent if scientists determine that a minimum size of more than two people are sufficient for a worldview that holds that new genetic information doesn't crop up and that the population only started with two.

    3) Darwinists who argue (2) against Creationists fail to take the arguments that Creationists make into consideration:

    a) Creation, as miraculous, can entail the increase in new genetic material as the population expanded.

    b) If no genetic material is created after the initial creation, then it can be observed that two people are sufficient to contain all possible base pair combinations. Two people contain 4 full sets of genetic material. That's enough.

    c) The argument assumes that all possible combinations exist in the human population. I believe that such has yet to be demonstrated. If an extensive lack of base pair combinations are missing from the human population, then the argument is merely academic.


  4. Those assumptions are essentially the same as Hardy-Weinberg equilibrium, which is a useful tool for showing how allele frequencies may change over successive generations, but is pretty much useless for analyzing real biological data.

    For one thing, humans can't randomly mate. "Random mating" in this context means that all individual of the population have an equal chance of mating with any other individual. Females must mate with males to produce offspring (sorry homo activists), so there's one assumption out the window.

  5. "...the population of Homo sapiens could not have been smaller than about 12,250..."

    They are telling me that I'm supposed to find a literal Adam and Eve incredulous, when they are telling me that I should believe that mostly chance-driven processes created a small city's worth of human beings all at one time? If the population was never less than 10,000, then that means all 10,000 of those evolved at approximately the same time, right? How on earth does that happen? Or am I just missing something here?

  6. If anyone is interested, here's a collection of links to Hugh Ross' ministry website Reasons to Believe on:

    Resources at RTB Relating to Human Origins