Galápagos Finches — A Paradigm of the Limits of Natural Selection?
Posted: 2020-11-20 02:33:00    (see more from evolutionnews.org)
Photo: Geospiza fortis, by putneymark via Wikimedia Commons (cropped).

Author’s note: Are Darwin’s finches “a particularly compelling example of speciation” as well as “evolution in action”? In a series of posts, I offer some notes on the question of whether macroevolution is happening on the Galápagos Islands. Please find the full series here.

So, may the Galápagos finches even be called a paradigm of the limits of natural selection? My answer: The “Darwin” finches — those “iconic birds whose facial variations have become a classic example of Charles Darwin’s theory of natural selection” (Nala Rogers in Nature 2016)1 — can indeed be seen as a prime example of the limits of natural selection, or “Sisyphean evolution” according to McKay and Zink. They are not, per the National Academy of Sciences, a “particularly convincing example for speciation.” 

Also Beyond Natural Selection

In this context I will mention that there is another phenomenon, at the DNA level, where natural selection fails almost completely as an explanation. The authors Lamichhaney et al. report (2015, p. 371): “Stringent variant calling revealed approximately 45 million variable sites [SNPs] within or between populations” (emphasis added).2 What are SNPs, or single-nucleotide polymorphism?

A single-nucleotide polymorphism (SNP; /snɪp/; plural /snɪps/) is a substitution of a single nucleotide at a specific position in the genome, that is present in a sufficiently large fraction of the population (e.g. 1% or more).

For example, at a specific base position in the human genome, the C nucleotide may appear in most individuals, but in a minority of individuals, the position is occupied by an A. This means that there is a SNP at this specific position, and the two possible nucleotide variations — C or A — are said to be the alleles for this specific position.3

Dog Breeds and Darwin Finches

In my book on the relevance of dog breeds for the theory of macroevolution, I noted the following about the SNPs: 

Regarding the “approximately 45 million variable sites [SNPs] within or between populations” in the Galápagos finches alone, the following can be said about the selection question.

The synthetic theory of evolution (= neo-Darwinism), which dogmatically postulated that all biological changes be controlled and directed by natural selection (including, of course, the molecular genetic level), has been clearly refuted by two important molecular points: (1) The number of SNPs (single-nucleotide polymorphisms) with approximately 45 million in the Galápagos finches exceed anything that could be imagined even up to a few years ago in terms of variation. For there is no natural selection, however strict, that could even come close to controlling this totally unexpected, overwhelmingly enormous amount of variation. (2) The same applies to the CNPs, which may number in the thousands, but for which I do not yet have an exact number. 

Some additional points are here (2017, p. 1): 

We find that two of the most pronounced genomic islands contain the ALX1 and HMGA2 loci, which are associated with variation in beak shape and size, respectively, suggesting that they are involved in ecological adaptation.

And note here in Science (2016, p. 470): 

Genotypes associated with large beak size were at a strong selective disadvantage in medium ground finches (selection coefficient s = 0.59).

Well, “a strong selective disadvantage” may be at odds with the idea of slow and smooth evolution as generally postulated by the synthetic theory — as I have repeatedly emphasized. Other revealing points are noted by Nala Rogers

By analysing DNA from medium ground finches that lived around the time of the drought, the researchers found that the large-beak HMGA2 variant was more common in birds that starved to death, while the small-beak variant was more common in birds that survived. This genetic shift is likely responsible for some of the reduction in beak size, the researchers say. [Emphasis added.]

Next, “Galápagos Finches — An Exceptionally Strong Natural-Selection Event?”

Notes

  1. https://www.nature.com/news/evolution-of-darwin-s-finches-tracked-at-genetic-level-1.19795
  2. Sangeet Lamichhaney, Jonas Berglund, Markus Sällman Almén, Khurram Maqbool, Manfred Grabherr, Alvaro Martinez-Barrio, Marta Promerová, Carl-Johan Rubin, Chao Wang, Neda Zamani, B. Rosemary Grant, Peter R. Grant, Matthew T. Webster & Leif Andersson (2015): Evolution of Darwin’s finches and their beaks revealed by genome sequencing. Nature518:371-375. In this paper I could not find the differentiation between the numbers of SNPs und CNVs (the possibly thousands of CNVs may have been included there).
  3. https://en.wikipedia.org/wiki/Single-nucleotide_polymorphism; see also https://de.wikipedia.org/wiki/Einzelnukleotid-Polymorphismus