Sunday, May 07, 2006

'Darwin's finches' revert to type

Darwin's finches show how man harms evolution, The Independent, 4 May 2006, Steve Connor ...

[Graphic: "medium ground finch," University of Miami.

See also "'Darwin's finches' revert to type," Aljazeera, which headline I have used (instead of the nonsensical "Darwin's finches show how man harms evolution," - how can man harm a natural process, let alone a mindless, purposeless one?) , and "Humans may be causing evolution to reverse," Independent Online, which is the same article. Also, some may be interested in a story at page 3 of today's Sydney Morning Herald, 'Darwin's evolutionary theory is a tottering nonsense, built on too many suppositions', which Google hit as a news search on "Darwin's finches" but doesn't seem to have anything directly about them in it.]

They were the birds that were said to have inspired Charles Darwin to formulate his theory of evolution more than 10 years after his famous visit to the Galapagos Islands. Darwin's finches iconically depicted how biological diversity and natural selection lead to the origin of new species - but now scientists have detected signs of evolution "in reverse". Biologists have found that one of Darwin's finches living in the remote Pacific archipelago has begun to revert to an earlier form because of interference caused by a growing human population. Humans are causing evolution to slip into reverse for one of the finch species that lives on the islands. Scientists have found that the finch is losing the distinguishing trait that was causing it to split into two different species - its beak. The medium ground finch [Geospiza fortis] is normally found in two distinct forms - one with a larger beak the other with a smaller one - but when humans come to live alongside the finch, this "bimodal" beak size tends to disappear. The scientists believe that the arrival of people on the islands may be causing evolution to run in reverse by causing the two extreme versions of the ground finch to revert to individuals with intermediate beak sizes. In effect, people appear to be unwittingly eliminating the evolutionary disadvantage of having a beak that is half-way in size between the two extremes, according to a study published in the Proceedings of the Royal Society B. As yet the researchers do not understand why people are having this effect but the implications are that the influx of tourists and migrants to the Galapagos is helping to eradicate a source of biological diversity that has made the islands famous. Professor Andrew Hendry of McGill University in Montreal, who led the study, said: "We need to make more effort to enable those species that are in the process of diversifying to continue to diversify and thereby generate new species. It is appropriate to describe it as evolution in reverse. It's an evolutionary split within a species that is being reversed and we think human activity is responsible," he said. ... [Sounds like another best evidence of Darwinism in action is unravelling? If Darwin's finches were true species (and not just varieties within a species), then they would not be able to "revert to an earlier form ." Irrespective of Dollo's law, which states that "Evolution is irreversible" (however, see `tagline' quotes for qualifications):

"In despair of ever finding an important pattern to evolution, some biologists assert that the only generalization that can be safely made is that which has been christened `Dollo's Law': Evolution is irreversible. The palaeontological record supports this generalization and no one seriously believes that the law will ever be violated. But is the idea so profound that it deserves a name? Evolution is a part of history. No part of history ever repeats itself. The irreversibility of evolution is no more and no less mysterious than the irreversibility of history in general." (Hardin, G., "Nature and Man's Fate," Rinehart: New York NY, 1959, p.92)

in this case if there is "evolution `in reverse'" (which is meaningless for a process that can go forward, backwards, and sideways, yet still be called "evolution"!), then that is good evidence that there never was any "evolution" to "reverse"!

Indeed, even the experts on Darwin's finches, Peter and Rosemary Grant, admit that instead of 14 species of finch there may be only 6 and even that with "additional study might necessitate yet further reduction" (conceivably down to 1?!):

"Writing in Science in 1992, the Grants noted that the superior fitness of hybrids among populations of Darwin's finches `calls into question their designation as species.' [Grant, P.R. & Grant, B.R, "Hybridization of Bird Species," Science, Vol. 256, 1992, pp.193-197] The following year, Peter Grant acknowledged that if species were strictly defined by inability to interbreed then `we would recognize only two species of Darwin's finch on Daphne,' instead of the usual four [Grant, P.R., "Hybridization of Darwin's finches on Isla Daphne Major, Galapagos," Philosophical Transactions of the Royal Society of London B, Vol. 340, 1993, pp.127-139]. `The three populations of ground finches on Genovesa would similarly be reduced to one species,' Grant continued. `At the extreme, six species would be recognized in place of the current 14, and additional study might necessitate yet further reduction." (Wells, J., "Icons of Evolution: Science or Myth?: Why Much of What We Teach About Evolution is Wrong," Regnery: Washington DC, 2000, pp.172, 312n)

As David Berlinski notes, "After three decades spent observing Darwin's finches in the Galapagos, P.R. and B.R. Grant were in the end able to state only that `further continuous long-term studies are needed'," which he also notes " is the conclusion invariably established by evolutionary field studies, and it is the only conclusion established with a high degree of reliability":

"But field studies have proved notoriously inconclusive when it comes to natural selection. After three decades spent observing Darwin's finches in the Galapagos, P.R. and B.R. Grant were in the end able to state only that `further continuous long-term studies are needed.' [Grant, P.R. & Grant, B.R., "Unpredictable evolution in a 30-year study of Darwin's finches," Science, Vol. 296, April 26; 2002, pp.707-711] It is the conclusion invariably established by evolutionary field studies, and it is the only conclusion established with a high degree of reliability." (Berlinski, D., "On the Origins of the Mind," Commentary, Vol. 118, No. 4, November 2004)!

I have added the above article and quotes to my "Problems of Evolution" book outline, PE "Natural selection ... Problems with best evidence ... Darwin's finches."

Stephen E. Jones, BSc (Biol).
"Problems of Evolution"

"In practice, however, evolution of the whole population in all of its traits is seldom reversed. The reason is simple. The heredity of most species of organisms is based not on a single locus but on thousands or tens of thousands of loci, many of which are represented in the population by more than just one or two alleles. Try to imagine most or all of this huge assemblage of allele systems being allowed to undergo various complicated changes in relative frequency, then reversing themselves and returning, all in concert, back to the starting point. Such an event is extremely unlikely. Even without the aid of this particular argument from genetics, biologists long ago recognized that evolution very seldom if ever reverses itself to any significant extent. This generalization is called DOLLO'S LAW, after Louis Dollo, a Belgian paleontologist who first derived it from his studies of fossils. Actually, Dollo's Law is not a true law in the sense of physics and chemistry, but rather a strong inference based on empirical evidence from the fossil record combined with some persuasive theoretical deductions from population genetics. Even so, it has some far-reaching implications. A well-known application of the law is that once a major anatomical structure has been lost or transformed into another structure, it can never be regained in its original form. The hind legs of seals, for example, which evolved into flippers as part of a marine adaptation in the remote past, can never return (Wilson, E.O., et al., "Life on Earth," [1973], Sinauer Associates: Sunderland MA, 1975, reprint, p.772. Emphasis original).

"Reversals are likewise common in evolution. The fossil record of elephants, for example, shows that the general trend toward greater size was reversed in several lines that evolved dwarf species, and reversals in the structure of the teeth accompanied the change in body size in each instance (Maglio 1972). Quite often a complex character may degenerate and return to its original state; thus winglessness in insects can be either a primitive condition as in silverfish (Thysanura) or a derived condition as in lice, fleas, and the many wingless species in almost every insect order that has evolved from winged ancestors. To be sure, there is a degree of irreversibility in evolution, as expressed by DOLLO'S LAW, which states that complex structures, once lost, are unlikely to be regained in their original form. However, the structure of the eye in snakes is different enough from thatof other vertebrates to suggest that it evolved to a new complex state from a reduced condition in a burrowing ancestor (Porter 1972). Of the several molars possessed by primitive Carnivora, the cats (Felidae) retain only the first, but in the lynx the second molar has reappeared (Kurten 1963). Thus some lost structures may indeed be regained." (Futuyma D.J., "Evolutionary Biology," [1979], Sinauer Associates: Sunderland MA, Second Edition, 1986, pp.297-298. Emphasis original)

"Louis Dollo, the great Belgian paleontologist who died in 1931, established a much misunderstood principle "the irreversibility of evolution" (also known as Dollo's law). Some ill-informed scientists think that Dollo advocated a mysterious directing force, driving evolution forward, never permitting a backward peek. And they rank him among the non-Darwinians who feel that natural selection cannot be the cause of nature's order. In fact, Dollo was a Darwinian interested in the subject of convergent evolution-the repeated development of similar adaptations in different lineages. Elementary probability theory, he argued, virtually guarantees that convergence can never yield anything close to perfect resemblance. Organisms cannot erase their past. Two lineages may develop remarkable, superficial similarities as adaptations to a common mode of life. But organisms contain so many complex and independent parts that the chance of all evolving twice toward exactly the same result is effectively nil. Evolution is irreversible; signs of ancestry are always preserved; convergence, however impressive, is always superficial.." (Gould, S.J., "Double Trouble," in "The Panda's Thumb: More Reflections in Natural History," [1980], Penguin: London, 1990, reprint, p.35)

'Dollo's Law' states that evolution is irreversible. ... There is no reason why general trends in evolution shouldn't be reversed. If there is a trend towards large antlers for a while in evolution, there can easily be a subsequent trend towards smaller antlers again. Dollo's Law is really just a statement about the statistical improbability of following exactly the same evolutionary trajectory twice (or, indeed, any particular trajectory), in either direction. A single mutational step can easily be reversed. But for larger numbers of mutational steps, even in the case of the biomorphs with their nine little genes, the mathematical space of all possible trajectories is so vast that the chance of two trajectories ever arriving at the same point becomes vanishingly small. This is even more true of real animals with their vastly larger numbers of genes. There is nothing mysterious or mystical about Dollo's Law, nor is it something that we go out and 'test' in nature. It follows simply from the elementary laws of probability." (Dawkins, R., "The Blind Watchmaker," [1986], Penguin: London, 1991, reprint, p.94)

"Thus, for example, Dollo's law of reversibility (see Gould, 1970b) only restates the general principles of mathematical probability for the specific case of temporal changes based on large numbers of relatively independent components. And Williston's law of reduction and specialization in modular segments may only record a structural constraint in random systems, thus following the same principles as my previous argument about the expanding right tail of complexity for life's totality. Suppose that, in overall frequency within the arthropod clade, modular species (with large numbers of similar segments) and tagmatized [fusion of segments] species (with fewer fused and specialized groupings of former segments) always enjoy equal status in the sense that 50 percent of habitats favor one design, and 50 percent the other. (I am, of course, only presenting an abstract `thought experiment,' not an operational possibility for research. Niches don't exist independent of species.) But suppose also that, for structural reasons, modular designs can evolve toward tagmatization, but tagmatized species cannot revert to their original modularity-an entirely reasonable assumption under Dollo's law (founded upon the basic statements of probability theory) and generalities of biological development. Then, even though tagmatization enjoys no general selective advantage over modularity, a powerful trend to tagmatization must pervade the clade's history, ultimately running to completion when the last modular species dies or transforms." (Gould, S.J., "The Structure of Evolutionary Theory," Belknap: Cambridge MA, 2002, Fifth printing, pp.901-902)

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