Tuesday, 17 March 2015

Genetic Bottleneck: YECs keep using that word. I do not think they know what it means...

Special creationist misuse of the scientific literature falls into two classes; (1) quote mining, where a paper is selectively quoted in order to change the original meaning of what the scientist was actually saying, and (2) a complete misunderstanding of the paper, where the special creationist, lacking even rudimentary knowledge of the scientific basics, cites a paper as evidence for special creation when it actually proves nothing of the sort.

That there is too much genomic diversity in the human race to have emerged from just two people living six thousand years ago, or six people living around 4500 years ago is hardly controversial in mainstream scientific circles. What this means is that the flood was not anthropologically global, and humanity did not exclusively descend from two people living around six to ten thousand years ago. In other words, we do not see evidence of a razor-sharp genetic bottleneck when we look at the human genome. Any theological position that is contingent on monogenism or an anthropologically global flood has been ruled out by the facts, and no amount of appeal to a literal reading of Romans 5:12 or the creation narratives will alter those facts.

It is amusing, if not disappointing to see how special creationists attempt to deal with these facts:
Some say that a "population bottleneck" never happened in man's history. Well, this is the latest in a growing line of academic papers on the subject:
While there is a growing list of academic papers on the subject, these have been completely misunderstood by the YECS given that none of them provide evidence that the human race descended from two people living six thousand years ago. Certainly, this paper has been completely misunderstood by the person citing it, given that it provides no support for the YEC belief that 6000 years ago, the human race began from two people living in Mesopotamia:

“[a]pplying ancient DNA calibration, we date the Y-chromosomal most recent common ancestor (MRCA) in Africa at 254 (95% CI 192–307) kya and detect a cluster of major non-African founder haplogroups in a narrow time interval at 47–52 kya, consistent with a rapid initial colonization model of Eurasia and Oceania after the out-of-Africa bottleneck. In contrast to demographic reconstructions based on mtDNA, we infer a second strong bottleneck in Y-chromosome lineages dating to the last 10 ky.” [1]
An out-of-Africa bottleneck is not the same thing as a bottleneck of two people living six thousand years ago in south-west Asia.
Evolutionary creationists do not deny that population bottlenecks have occurred in human history. However, what they deny is that there has been a razor-sharp genetic bottleneck of six around 4500 years ago around the time of the flood, or two around 6000 years ago.When population geneticists talk about bottlenecks, they are referring to numbers in the thousands, which is quite small from a population point of view, but nowhere near the two people required for monogenism. The bottleneck about which mainstream scientists speak is not the bottleneck of YEC. Typical of this "growing line of academic papers" is a 2011 Science paper by Li and Durban that examined the genomes of Chinese, Korean, European, and African humans and found that:
From a peak of 13,500 at 150kyr ago, the Ne dropped by a factor of ten to1,200 between 40 and 20kyr ago, before a sharp increase, the precise magnitude of which we do not have the power to measure. We also observed a less marked bottle neck in YRI from a peak of 16,100 around 100–150kyr ago to 5,700 at 50kyr ago, recovering earlier than the out-of-Africa populations, with an increase back to 8,700 by 20kyr ago, coinciding with the Last Glacial Maximum. All populations showed increased Ne between 60 and 200kyr ago, about the time of origin of anatomically modern humans. [2]
The data show two bottlenecks. The first was around 10,000 individuals around three million years ago. The second bottleneck, for Chinese, Korean, and European genomes was around 1,200 between twenty to forty thousand years ago. For Africans, the bottleneck was somewhat less severe at 5,700 around fifty thousand years ago. Absent from this data is any evidence that within the last 3 million years our ancestry was reduced to a bottleneck under one hundred, let alone two:

Source: Nature (2011) 475:493-497
Given that such fundamental misunderstanding of the scientific literature is disturbingly common among special creationists, it is imperative that they try to understand the fundamentals of population genetics before posting nonsense on the subject, stop trying to shoehorn the data to make it fit with monogenism, and accept the population genetic data as it is. For those wanting to fill lacunae in their knowledge, an excellent overview for the layperson is this ongoing series by evolutionary geneticist Dennis Venema.


1. Karmin M et al A recent bottleneck of Y chromosome diversity coincides with a global change in culture” Genome Res. (2015)

2. Li, H. and R. Durbin.  “Inference of human population history from individual whole-genome sequences.”  Nature (2011) 475:493-497.