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

Wolf-Ekkehard Lönnig
Photo: Galápagos finch, by kuhnmi, via Flickr.

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.

From a Princeton University press release, “Gene behind ‘evolution in action’ in Darwin’s finches identified”1:

“It was an exceptionally strong natural-selection event,” said Peter Grant, adding that because Daphne Major is in an entirely natural state the occurrence was completely unaffected by humans. [Emphasis added.]

An “exceptionally strong natural-selection event” was not expected by Darwin or the neo-Darwinians. Rather, the following, as I have written in my book The Evolution of the Long-Necked Giraffe:

Darwin imagined the origin of species (and, in fact, of all life forms) by selection of “infinitesimally small changes”, “infinitesimally slight variations” and “slow degrees” and hence imagined “steps not greater than those separating fine varieties”, ”insensibly fine steps” and “insensibly fine gradations”, “for natural selection can act only by taking advantage of slight successive variations; she can never take a leap, but must advance by the shortest and slowest steps” or “the transition [between species] could, according to my theory, be effected only by numberless small gradations” (emphasis added). Virtually the same answer is presented by neo-Darwinism today.  

From, “Galápagos Finch-Beak Size Locus Identified by Resequencing,”2 via GenomeWeb:

The smaller beak-associated haplotype dominated amongst medium ground finches that survived the drought, turning up in some 61 percent of 37 surviving birds. But it is less common in a set of 34 medium ground finches that perished in the period of lower food availability, turning up in just one-third of those birds. [Emphasis added.]

As for this “exceptionally strong natural-selection event,” this is by no means an all-or-nothing selection (as the impression is sometimes given). Rather, the alleles are retained. 

Life “Takes a Leap”

So, this “evolution” does not proceed by “infinitesimally small changes,” “infinitesimally slight variations” and “slow degrees” and “steps not greater than those separating fine varieties,” “insensibly fine steps” and “insensibly fine gradations,” but (to rephrase Darwin) it “takes a leap, instead of advancing by the shortest and slowest steps.”

From an Uppsala University press release, “Evolution in action detected in Darwin’s finches”3:

Variation in beak morphology among these species is determined by the action of many gene variants but two genes with particularly important effects have now been identified, HMGA2 that affects beak size and ALX1 that controls beak shape. HMGA2*L and HMGA2*S promote the development of large and small beaks, respectively, while ALX1*P and ALX1*B are associated with the development of pointed and blunt beaks, respectively. [Emphasis added.]

From a report in the Christian Science Monitor, “Darwin’s finches are pecking their way through evolution”4:

But that [selection] doesn’t mean that the HMGA2 variation for larger beaks in the medium ground finches has gone extinct, [Leif] Andersson says. There are still individuals with that version of the gene and larger beaks

And, as natural selection dictates, different ecological pressures may lead to a resurgence of that variant, too. “As long as both variants are present in the medium ground finch, they may to respond to what is available, so to speak,” Andersson says. It will depend on which birds can forage for food and reproduce most effectively. [Emphasis added.]

“Sisyphean Evolution”

The morphological/anatomical effects of the alleles on beak formation are thus briefly yet clearly outlined. For (other) pleiotropic effects please see the original papers. 

This “Sisyphean evolution of Darwin’s finches,” which can — for the reasons given above — be extrapolated to all the so-called genera and species of these birds, is definitely not an example of “a particularly compelling example of speciation,” of “evolution in action,” of “an iconic model for studies of speciation and adaptive evolution” (Lamichhaney et al. in Nature 201526).

Next, “Galápagos Finches — Some Contradictions Solved.”

Notes

  1. https://www.princeton.edu/news/2016/04/21/gene-behind-evolution-action-darwins-finches-identified
  2. https://www.genomeweb.com/sequencing-technology/galapagos-finch-beak-size-locus-identified-resequencing#.Xi7qCCMxn-g 24 https://www.uu.se/en/news-media/press-releases/press-release/?id=3208&typ=pm
  3. https://www.csmonitor.com/Science/2016/0422/Darwin-s-finches-are-pecking-their-way-through-evolution
  4. https://pubmed.ncbi.nlm.nih.gov/25686609/