A False Trichotomy
|March 14, 2011||Posted by Jonathan M under Intelligent Design|
I recently promised that I would discuss the latter half of chapter 4 of Daniel Fairbanks’ 2010 book, Relics of Eden, in which Fairbanks attempts to demonstrate common ancestry based on considerations of maternally-inherited mitochondrial and paternally-inherited Y-chromosomal DNA sequences. Or, put more accurately, Fairbanks attempts to demonstrate that humans and chimpanzees are more closely related than either is to gorillas. Fairbanks’ methodology here, however, presupposes (and does not demonstrate) that indeed there is such a hereditary relationship linking humans, chimpanzees and gorillas. If one chooses to interpret mere genetic similarities as evidence for common descent then, indeed, within the framework of that paradigm, Fairbanks’ conclusions may be allowed to stand. But given that modern Darwinians are not even close to articulating a plausible — or even viable — naturalistic mechanism which can account for such evolution from a common ancestor, are we not justified in, at the very least, reserving our judgment until such a mechanistic basis is forthcoming?
The majority of Fairbanks’ arguments for common ancestry (such as shared mobile element or intron inserts, and shared “mistakes”) can be readily accounted for in terms of a common mechanism (i.e. constraints on integration, or similar genetic instabilities or mutation “hotspots”). And there is no decisive way to distinguish common ancestry from common design with regards to unqualified appeals to “similarity”. Does it not stand to reason that a designer might use similar genes and tools to perform similar functions in different organisms?
In fact, if we are going to let all the evidence speak, then why not take into account the evidence against common ancestry? Since we’re on the topic of the Y-chromosome, what about this study published in Nature just last year, which yielded evidence that the male-specific portions of the human and chimp Y chromosome “differ radically in sequence structure and gene content,” suggesting “wholesale renovation,”? The Nature News report noted that,
The common chimp (Pan troglodytes) and human Y chromosomes are “horrendously different from each other”, says David Page of the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, who led the work. “It looks like there’s been a dramatic renovation or reinvention of the Y chromosome in the chimpanzee and human lineages.”
Fairbanks does make note that some studies suggest that chimpanzees and gorillas were more closely related, with some even suggesting the highest similarity between humans and gorillas. But he largely dismisses this as “analogous to the signal-to-noise problem in broadcast television and radio.” He notes,
Because random variation and the laws of probability govern inheritance of DNA, we expect to see some random fluctuations, like the television noise, in DNA comparisons. A single isolated study is not always representative of an overall pattern. Although most studies may support a particular pattern, a few studies here and there might seem to contradict it because of the noise. Others might oversupport the real pattern and suggest a closer relationship than what actually exists. In other words, the noise varies in both directions.
But are these dis-concordant phylogenies simply anomalous data? Are they simply “noise”? Just how many of these loci are non-congruent? I submit that the problem extends somewhat deeper than Fairbanks is willing to let on. Indeed, one paper published in the year 2000 suggested that,
60% of the loci and approximately the same proportion of phylogenetically informative sites support the human-chimpanzee clade. The remaining 40% of loci and sites support the two alternatives equally. [emphasis added]
Now, in fairness, some studies (such as this one from 2007) have obtained a somewhat smaller figure for the loci which do not support chimpanzees as being our closest genetic relatives when a larger data set was analysed. In the case of the cited 2007 paper, the authors note that “for about 23% of our data set chimpanzees are not the closest genetic relatives to humans.” 23% is no small percentage. That’s almost a quarter of the data which is non-congruent. In addition, Patterson et al. (2006) suggest a range of 18-29%.
Now, this is not to say that there is not a possible — indeed, perhaps plausible — explanation for this non-congruence (such as random sorting of allelic lineages, and the joint effect of recombination and genetic drift). But just as there may be plausible explanations for the lack of support for common ancestry with respect to the fossil record, one needs to be careful that one not think a rationalisation of non-phylogenetic-congruence constitutes evidence for Darwinian Theory. Given the sheer lack of evidence for the causal sufficiency of any given naturalistic mechanism, one ought to treat such grand propositions with a rational skepticism until one is offered some truly spectacular evidence for common ancestry. To date, no such spectacular confirmatory evidence has been forthcoming.