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 PrintableVersion Darwin's finchesDr. Nancy Darrall sees a big mistake for Darwin in this anniversary yearIn virtually every biology textbook, Darwin’s finches are quoted as a key proof of the theory of evolution. For example: ‘It was, however, the diversity of adaptive structures shown by the 13 species of finches found within the archipelago which had the greatest influence on Darwin’s thinking on the mechanism of the origin of species’ (Biological Science 1&2, Taylor Green & Stout, 1997, Cambridge University Press). However, they are not mentioned in Darwin’s book The Origin of Species, nor is there any discussion in his diary kept during the voyage of HMS Beagle. David Lack’s book Darwin’s Finches popularised the myth that the finches were instrumental in shaping Darwin’s thinking. Frank Sulloway, writing in the Journal of the History of Biology and a letter to Nature in the 1980s, exploded this myth. Ignoring his mentorDarwin was impressed by the variation within species of plants and animals. He was particularly interested in the enormous variation in domesticated animals such as pigeons, but he also noted the variation in the natural plants and animals he saw on his voyage. However, in his writings, he ignored the earlier work of Linnaeus, a Christian and a biologist, who after considerable study of plant and animal life concluded that the originally created kinds were probably at the level of the genus not species. He also ignored the work of his mentor, Professor of Botany at Cambridge, J.S. Henslow, whose work demonstrated variation within created kinds. Instead, Darwin took the variation he saw as evidence of evolution and disproof of the creation account. He assumed that the variation was the result of changes which could eventually lead to the development of new species. If Darwin had made careful observations of the Galapagos finches, what would he have seen? David Lack showed that the beak size and shape are clearly linked to the preferred food of the various species of finches in the islands. The small ground finches take the smaller softer seeds and the large ground finch can break open and extract the soft kernel from bigger, harder seeds. The depth of the beak plays a big part in this difference and it varies from around 7mm in the smallest of the finches to 24mm in the biggest. Not separateThere are ground finches, tree finches, cactus finches, warbler finches and woodpecker finches: 14 to 15 species in total. One very interesting thing about the beak size is that there is a continuous variation in size from the smallest to the largest species. As well as looking at the variation in appearance and the breeding habits of the birds, we can look at differences in DNA. All the finches have very similar DNA patterns, but there are some small differences which form a number of recognisable patterns. The same patterns crop up across all the six ground finches. This shows that the species are not completely separate breeding groups. Genes are passing between the species as they cross breed with each other, so giving the continuous variation in size. Oscillations of sizePeter and Rosemary Grant used one island, Daphne Major, in the Galapagos as a research laboratory over the 30-year period of their work from the 1970s. In a drought year, up to 80% of the birds can die; those best able to find food survive. In some droughts, those with larger bodies and beaks survive, in other droughts those with smaller bodies and beaks survive. Each drought acts as a sieve; only a few remain, but all are still finches. In the wetter years, beak sizes return to earlier values as those with intermediate size beaks do better and raise more chicks. So, we see oscillation in size back and forth reflecting oscillation in rainfall from year to year. Even the recent trend towards smaller beak size remains within the original range and can be explained by interbreeding between the species of finches. One kindCreation biologists today view all the Galapagos finches as one originally created kind. In Genesis 1 we read that plants and animals were ‘created…. according to their kinds’. That does not preclude variation within kinds. Fascinating as it would be to know about the originally created kinds, this can never be, because of the worldwide flood in the time of Noah. Plants recolonising after the flood must have survived among mud and rocks and animals without mature grasslands and woodlands in which to live. Variation within the originally created plants and animals would enable these colonisers to survive and succeed in the face of a variety of hostile environments. The Galapagos finches provide the creation biologist with a microcosm of the post-flood world. There are a variety of habitats on the islands and finches have exploited these successfully by partial separation of the original flock into the 14-15 species, each with a characteristic range of beak and body sizes. Fluctuating marketThe Grants made the same error of extrapolation as Darwin. They have taken the difference in body and bill size between wet and drought years and have predicted that after 200 years a new species of finch will appear. What they omitted was their own observations that sizes oscillate and usually return to earlier values. Jonathan Wells comments that this is ‘like a stock promoter who claims a stock might double in value in 20 years because it increased 5% in 1998 but doesn’t mention that it decreased 5% in 1999… As Berkeley law professor and Darwin critic Phillip Johnson wrote in The Wall Street Journal in 1999: “When our leading scientists have to resort to the sort of distortion that would land a stock promoter in jail, you know they are in trouble”’. Sources of information for this article and further reading: D. Tyler, Darwin’s Mentors Origins (Journal of the Biblical Creation Society), in press 2008 © Evangelicals Now - March 2009 |
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