Professor Jerry Coyne can’t seem to leave the Adam and Eve question alone. In a recent post, Professor Coyne criticizes Bryan College in Dayton, Tennessee, for requiring its teaching professors to sign an updated “statement of belief” which, for the first time, explicitly affirms the existence of an historical Adam and Eve. Since Bryan College describes itself as “a nondenominational evangelical Christian college named after William Jennings Bryan: statesman, orator, and renowned prosecuting attorney in the famous Scopes Evolution Trial,” this requirement should hardly occasion surprise. What would be surprising is if the college didn’t require its professors to believe in a literal Adam and Eve.
In a related post published late last year, Coyne explains in detail why he is convinced that science has ruled out the existence of Adam and Eve:
The facts first. Sheehan et al., building on an earlier paper by Li and Durbin (references below), calculated that the minimum population size associated with the worldwide expansion of humans out of Africa about 60,000 years ago was 2,250 individuals, while the population that remained in Africa was no smaller than about 10,000 individuals. For population geneticists, this is the “effective population size,” invariably smaller than the census size, so these are minimum estimates, and ones derived from conservative assumptions. The population sizes are estimated by back-calculating (based on reasonable estimates of mutation rates and other parameters) how small an ancestral population could be and still give rise to the observed high level of genetic variation in our species.
Note: 2,500 is larger than two.
This means, of course, that Adam and Eve couldn’t have been the literal ancestors of all humanity.
Evidently math is not Professor Coyne’s forte.
Note: 2,500 isn’t the same as 2,250.
Note: 2,250 + 10,000 = 12,250.
The math lesson is over.
Coyne goes on to say that even these figures are under-estimates: they represent “the ‘effective population size,’ invariably smaller than the census size.”
I invite readers to have a look at the following article by Luke J. Harmon and Stanton Braude, of Princeton University:
Conservation of Small Populations: Effective Population Sizes, Inbreeding,
and the 50/500 Rule
I shall quote a brief extract:
There is no such thing as “the effective size” of a population. Different effective population sizes help us to estimate the impact of different forces. The effective size you estimate will depend on the scientific question you are trying to address (Box 12.1). Estimating the appropriate effective population size is crucial in biology; in most (but not all) cases, effective population size will be smaller than the actual number of organisms in the population. Think for a moment about why
this is so. A conservative rule of thumb used by some biologists is
that N_e [the effective population size – VJT] is usually about one-fifth of the total population size (Mace and Lande, 1991). Using such a rough estimate is risky because N_e can be larger than the census size of the population, depending on the history of the population and the particular N_e under consideration.
It’s rather embarrassing when a biology professor makes mistakes in his own field, isn’t it?
UPDATE: A final suggestion for Professor Coyne. Coyne claims that the effective population sizes he cites are “based on reasonable estimates of mutation rates.” Coyne is assuming here that the mutations are natural and undirected. If Coyne wants to refute the Adam and Eve hypothesis as entertained by believers in intelligently guided evolution, then the question he really should be asking himself is: what would the effective population size need to be, if the mutations that gave rise to the human line were artificial and directed?