“Darwin’s Finches”: Galápagos Islands as an Evolutionary Model
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 have offered some notes on the question of whether macroevolution is happening on the Galápagos Islands. Please find the full series here.
Taking the facts and arguments presented together, it appears to be clear that no macroevolution is happening in “Darwin’s finches” on the Galápagos Islands.
The following is the English translation of some especially relevant and up-to-date points from a discussion1 with Professor Dr. Reinhard W. Kaplan 1991. He was the director of the Institute of Microbiology (Lehrstuhl für Mikrobiologie) at the Johann Wolfgang von Goethe Universität, Frankfurt am Main2. He did not continue the discussion.
“Evolution on an isolated island like the Galápagos, …”
The “evolution” on the Galápagos Islands is one of the best examples against the model favored by Prof. K. Because starting from the “isolated island,” the new founder populations should grow rapidly, continuously add beneficial hereditary changes, quickly displace their original populations and thereby become large populations themselves. It is now just one of the more recent significant biological discoveries that island populations do not meet the criteria (which are decisive for the question of the correctness of neo-Darwinism) for displacement of the original populations and expansion into large populations. In this context I refer to the excellent monograph by J. A. Drake et al. (1989), Biological Invasions (Wiley, Chichester, New York).
Would it really occur to anyone that the Galápagos finches might conquer mainland South America, displace populations there, and, if transferred to southern Europe and Africa, spread in the same way as, e.g., the European house sparrows in North America?
It is exactly the other way around: the island populations must be protected from invasion by widespread continental species! Braun reports (1989, p. 86) empirically derived rules for this question, for example: “Isolated environments with a low diversity of native species tend to be differentially susceptible to invasion.” “…species that are successful invaders tend to be native to continents and to extensive, non-isolated habitats within continents” (p. 92). “The fact that there are almost no good examples of successful invaders of continents that have come from small islands and other depauperate faunas … suggests that biotic resistance from diverse native species can be effective in repelling invaders” (p. 96) (emphasis added, here as in quotations throughout this post).
Macdonald et al. 1989, p. 234: “Although only a small percentage of the world’s land and freshwater avifauna occurs on oceanic islands ‘93% of the 93 species and 83 subspecies of birds that have become extinct since 1600 AD have been island forms’ (King, 1985).”
Honegger (1981, p. 235) lists two amphibians and 28 reptile taxa known to have become extinct since 1600 AD. The reptiles were all island forms and introduced species are implicated in the extinction of at least eight of them and one of the two amphibians.
Loope et al. 1989, p. 272: “The rigor of natural selection in such an evolving insular system may be relaxed by a large number of bottle necks (founder events) many groups have undergone in island hopping. … in many instances (the island forms) may not be so well adapted as the ‘general purpose genotypes’ of invasive introduced species.”
Pimm 1989, p. 355: “Species with larger ranges were more likely to be successful than species with smaller ranges. … Many introductions will succeed only if their numbers can increase quickly, beyond the small population size where extinction is likely.” The same author on p. 352: “The chance of extinction rapidly increases as population sizes decrease. Even in a perfectly constant environment, small populations face risk of extinction from demographic accidents — the chance fluctuations of deaths and births, and consequent changes of numbers and sex ratios….Another risk of becoming extinct is a low rate of population growth.”
The latter observations are particularly informative for the question of the evolution of species in small populations in 100,000 to 10,000,000 years (see Prof. K. above). The postulated macroevolution is unlikely for demographic and genetic reasons and can therefore not be accepted as a general rule for the origin of species.
Other authors have come to similar conclusions. Wills (1990, p. 398) discusses the problem in connection with “mitochondrial Eva” and an average population size of 5,000 women: “Such small sizes would have to be maintained for thousands of years with an attendant risk of extinction.” And he makes the following comparison: “The risk posed to the survival of the population in [this] … case is equivalent to the risk of crossing the Niagara Falls on a tightrope.”
Rabb and Lacy 1990, p. 612, on the topic of endangered-species biology:
Genetic homogeneity can imperil a species, but such inbreeding occurs as a consequence of population decline and fragmentation. It is just one of several interacting factors that come into play when a population becomes so small that its fate is determined more by randomness than by fitness. … Once populations are reduced and isolated, deleterious genetic and demographic factors ensue that serve to weaken further the survival of the species. The smaller populations also become progressively more vulnerable to environmental catastrophes. Even with amelioration of environmental circumstances, for example, provision of security in protected areas or zoological parks a species may go too far down the so-called “extinction vortex” of multiple causes to be recoverable.
Small populations over large numbers of generations with many recessive mutations are therefore an extremely unfavorable starting point for explaining the sudden appearance of Cambrian and other life forms and the fact that the temporal maxima of the construction plans and higher systematic categories occur before the lower ones!
With populations of approximately 10,000 individuals (see above: 5,000 women) and 1 million generations, 10 billion individuals would have been necessary for speciation. Was there really no chance of fossilization? The geologists Bennison and Wright, following the work of Shaw, calculate an average of 1 fossil per 1 million individuals! Even Galápagos finches have been found in fossil form! (See Grant 1984). And what about foraminifera, corals, brachiopods, cephalopods, etc., which are so well documented?
“… Galápagos, where Darwin received inspiration for his theory.”
According to several historians of science, this is a myth. Darwin was only made aware of the differences in, e.g., Mimus species by ornithologist John Gould after his return to England. “In retrospect, he [Darwin] was astonished at what he saw there” (Berry 1984, p. 1).
The following from Sull0way’s paper (1982, pp. 57-58) on “The Beagle Collections of Darwin’s Finches (Geospizinae)”3 and my subsequent comment are an addition made September 23, 2020 (the footnotes are Sulliway’s):
The celebrated ornithologist John Gould, who was closely associated with the Zoological Society, lost no time in examining and naming the unusual finches that Darwin had brought back from the Galápagos Islands. At the very next meeting of the society (10 January), Gould described these birds as twelve new species, which he placed in one genus and two closely allied subgenera (Geospiza, Cactornis, and Camarhynchus). Moreover, he astutely realized the basic peculiarity of these finches, namely, that ‘the bill appears to form only a secondary character.’ Soon afterwards Gould recognized Certhidea olivacea, the Warbler Finch, as a thirteenth species of the group, belonging to yet another genus16.
Darwin, who was at this time residing in Cambridge, did not learn of the details of Gould’s analysis until he moved to London in early March of 1837 in order to have closer contact with the specialists working on his collections. Gould’s findings, communicated to Darwin during a meeting with the eminent ornithologist, provided Darwin with a number of surprises17. While in the Galápagos, Darwin had been rather unclear about the precise relationship among the various finchlike species he had encountered there. In particular, he had misidentified several finch species as the forms that they, through extensive evolutionary radiation, now appear to mimic. For example, he had considered the Cactus Finch, Cactornis scandens, to be a member of the Icteridae (the family of the orioles and blackbirds); and he had classified the Warbler Finch, Certhidea olivacea, as a ‘wren’, or warbler. It appears, moreover, that Darwin initially distinguished as separate species of finches only 6 of the eventual 13 forms that Gould named in early 1837. Hence Darwin’s finches only really became Darwin’s finches after Gould rectified many of Darwin’s earlier field misclassifications, and thereby clarified the unity and complexity of the group18. More important still for Darwin’s evolutionary thinking, Gould (1837d) declared that 3 of the 4 island forms of Galápagos mockingbird brought to England by Darwin were distinct species, a possibility that Darwin had already asserted ‘would undermine the stability of Species’. For the Galápagos as a whole, Gould pronounced 25 of the 26 land birds as new and distinct forms found nowhere else in the world. Darwin was frankly stunned, not only by the realization that three separate species of mockingbirds indeed inhabited the different islands of the Galápagos, but also by the fact that most of these Galápagos species, even though new, were closely related to those found on the American continent19. His conversion to the theory of evolution, which took place shortly after his meeting with Gould in March of 1837, was a direct consequence of these two conclusions.
This “conversion” constitutes, in fact, an astonishing confusion and misunderstanding of the morphological species concept (cf. here) by Darwin as well as Sulloway.
“This branching out (typogenesis) usually happens relatively quickly, as the pace of evolution is usually high during adjustment to new niches (ways of life).”
Typogenesis did not take place in the Galápagos! Even the formation of species in the finches is still doubtful: “Intersterility is not known in Darwin’s finches. Intrageneric hybrids among ground finches are certainly both viable and fertile … and probably the same is true for intergeneric hybrids between tree finches and warbler finches” (Grant 1986, p. 353). “… [S]ix species of Geospizina (finches) in the Galápagos Islands show a genetic distance from 0.004 to 0.065” (Nei 1987, p. 245). In humans, the differences are between 0.01 and 0.03. The small genetic distances of islanders are in clear contrast to the morphological differences that we also find in domestic animals. (These are further proofs that morphological and genetic distances need not be coupled with each other.)
With domestic animals one normally refrains from establishing new systematic species and genera, — in nature, however, one creates numerous morphospecies and morphogenera, regardless of the genetic situation, which are often used uncritically as evidence of evolution.
In their study, Loop et al. (1989, pp. 271-272) pointed to the general trend of little genetic distance between morphologically and ecologically strongly diverging (but closely related) island “species.” In the Hawaiian Tetramolopium (Asteraceae), for example, Lowry and Crawford examined 19 populations of 7 “species”: “The ‘mean genetic identity for pairwise comparison…is 0.95, a very high value normally obtained for conspecific plant populations.'”
The flightless Galápagos cormorants clearly illustrate the degeneration of structures, a process that seems to occur rather quickly in small populations through inbreeding involving homozygous occurrence of numerous recessive alleles (already accumulated in previous larger populations).
What we detect here is not typogenesis, but typolysis! This also explains the low resistance of island populations to invaders and the high rate of extinction.
The comparison with domestic animals illustrates the situation in several aspects. In both groups we find:
- Little genetic distance, but great morphological variability within the species (with dogs, e.g., one could set up a new family with several genera and over 400 “species,” something similar with the many races of pigeons, or of chickens, or horses, etc.).4
- Formation of numerous ecotypes.
- Small populations and inbreeding as the starting point for “speciation.”
- Numerous recessive genes compared to the wild type.
- Genetic drift. Originally stricter selection conditions (for differential survival) are no longer applicable, but later there is also selection for certain phenotypes and ecotypes.
- Low resistance compared to widespread wild populations.
- Frequent degeneration and breakdown of structures; physiological compensation options.
- No formation of new primary species.
Conclusion: No explanation of the paleontological findings (among others)!
“If a niche has been occupied for a long time by a species that fully utilizes it, rich in individuals, progressive hereditary variants are rare for a long time, and evolution seems to stagnate (typostasis). If adverse environmental changes are not absorbed (buffered) by hereditary variants resistant to them, the population will die out.”
Since the species with a large number of individuals, due to the recurrent mutations that occur regularly, must have a significantly greater allelic potential than a small population, it is questionable why the former may have unfavorable environmental conditions to which they cannot not adapt, while the individual poor population with low genetic potential (see above) should be capable of rapid evolution! As a rule, the widespread species with its much greater genetic potential should be able to adapt to the new conditions in many places at the same time through allele substitution and thus should have better chances of survival than the small population with its few possibilities in the same situation — which, as we have seen — is, in fact, the case.
“According to the theory, the pace of evolution can vary from (geologically) fast to slow, depending on the circumstances.”
Since the term “evolution” implies the origin of all forms of life, it should be noted here that Prof. K.’s theory cannot explain the origin of the primary species or the higher systematic categories and Baupläne. According to the available findings, it is the pace of degeneration that can vary rapidly to slowly, depending on the circumstances geologically.
For a full presentation of this series including supplements, please see my Internet Library here.
- See W.-E. Lönnig (2014): Unser Haushund — Eine Spitzmaus im Wolfspelz?http://www.weloennig.de/Hunderassen.Bilder.Word97.pdf