Evolutionary Creationism: A Christadelphian Perspective: Ron Cowie claims observed genetic diversity could come from two people

Thursday 5 March 2015

Ron Cowie claims observed genetic diversity could come from two people

Evidence from genetics has comprehensively ruled out the possibility that the entire human race could have descended exclusively from two people living six thousand years ago. Ignoring the fact that such a small population would become dangerously inbred and crash to extinction, there is simply not enough time for the genomic diversity we see in the human race to have emerged from two people living a few thousand years ago.

In a post on the Christadelphian Answers website, Ron Cowie asks “how did such genetic diversity and racial characteristics come from one family?” [1] and proceeds to answer by offering a literal reading of a few Bible verses (overlooking the fact that alternative interpretations are possible). This approach is not convincing given that an interpretation of a verse is not the same thing as the original inspired message. Furthermore, it creates a needless conflict by pitting the witness of the natural world against a human interpretation of the Bible, one that not only discredits the Bible, but causes needless crises of faith in scientifically literate believers.

Cowie’s explanation runs aground for two reasons. The first is that he ignores the main problem – insufficient time for the genomic diversity we see in the human race if we hypothesise recent universal descent from two people – and misinterprets a scientific paper on genetic variation and race. He writes:

There are few genetic differences between any two individuals, about 0.1% of the genome. Of this 0.1%, 85-90% of genetic variation can be found between individuals from the same population. The remaining 10-15% accounts for differences between populations. The genetic difference between populations or ‘races’ is small.

Cowie forgets that small is a comparative term, and fails to demonstrate that the paper provides any support for recent human descent from two people living 6000 years ago. In fact, the paper explicitly refutes Cowie's antievolutionary thesis:

Allele frequencies in populations can be compared to assess the extent to which populations differ from one another. The overall pattern of these genetic distances, summarized in a network diagram, shows several important trends. First, populations tend to cluster according to their geographic distance from one another. This is to be expected, as geographically distant populations were less likely to exchange migrants throughout human evolutionary history. Second, the African populations are more diverse, a pattern consistent with many studies that have compared in various human populations. Third, the largest genetic distance is seen between African and non-African populations. Finally, because this network is based on Alu insertion polymorphisms, it is possible to designate unambiguously the allelic state of the ancestral human population as one in which none of the insertions would be present. This allows us to 'root' the tree and shows that the root falls closest to African populations. All of these findings, which are in accord with many other studies based on different types of genetic variation assessed in different samples of humans, support an evolutionary scenario in which anatomically modern humans evolved first in Africa, accumulating genetic diversity. A small subset of the African population then left the continent, probably experienced a population bottleneck and founded anatomically modern human populations in the rest of the world. Of special importance to discussions of race, our species has a recent, common origin. (Emphasis mine) [2]

Clearly, the authors of this paper do not believe it supports special creation, and regard the evidence as supporting an evolutionary origin. It is hard to understand why Cowie would cite this paper in the first place, as it is consistent with an evolutionary origin of the human race.

Secondly, Cowie focuses on skin colour as if it alone was the only area of genetic diversity in the human genome. It is not. Genetic diversity is found in genes such as that coding for angiotensinogen, which codes for one of the proteins involved in regulating blood pressure, and CYP2D6, an enzyme of importance in drug metabolism, [3] as well as in non-coding DNA [4]. The diversity in the genome, (which is far, far more than the few genes associated with skin colour) not only rules out universal human descent from two people 6000 years ago, but also shows that human population size has been no lower than a few thousand people. As geneticist (and evangelical Christian) Dennis Venema notes:

Studies based on SNP/LD approaches have now estimated ancestral population dynamics for various human groups over time in more detail than is possible with mutation-based estimates. African groups have a higher effective population size (~7,000) than do non-African groups (~3,000) over the last 200,000 years. This approach, though based on methods and assumptions independent of previous work, nonetheless continues to support the conclusion that humans, as a species, are descended from an ancestral population of at least several thousand individuals. More importantly, the scalability of this approach reveals that there was no significant change in human population size at the time modern humans appeared in the fossil record (~200,000 years ago), or at the time of significant cultural and religious development at ~50,000 years ago.

Taken individually and collectively, population genomics studies strongly suggest that our lineage has not experienced an extreme population bottleneck in the last nine million years or more (and thus not in any hominid, nor even an australopithecine species), and that any bottlenecks our lineage did experience were a reduction only to a population of several thousand breeding individuals. As such, the hypothesis that humans are genetically derived from a single ancestral pair in the recent past has no support from a genomics perspective, and, indeed, is counter to a large body of evidence. (Emphasis mine) [5]

This is reinforced by recent research by Richard Durbin and Heng Li which shows that the European and Asian population went through a bottleneck of around 1200 people between 20-40 thousand years ago, while the African population was a little under 6000 people around 50,000 years ago. [6] This is nowhere near a bottleneck of 2 people living 6000 years ago. There is simply no evidence to support universal recent human descent from Adam and Eve, (or for that matter an anthropologically universal flood) as the genomic data rules it out.

Postscript

Cowie’s failure to address the fact that there is no sharp genetic bottleneck in the human genome as universal human descent from a recent primal pair (or an anthropologically universal flood) would demand, is disappointing. Even more worrying is that he refers those looking for more information not to a credible mainstream scientific source, but to a YEC book edited by Don Batten, a YEC agricultural scientist, and whose contributing writers David Catchpoole (plant physiology), Jonathan Sarfati (inorganic chemistry), and Carl Wieland (medical doctor), who like Batten are not experts in population genetics and are writing well outside their professional spheres of competence.

Batten in particular has been strongly criticised for making factually inaccurate statements [7] and advancing arguments which betray a profound ignorance of the scientific literature. [8] It is extremely disappointing to see Cowie rely on such unreliable, discredited sources to bolster a literal reading of the creation narratives.

References