The original question was:
I have recently returned from a tour of the Galapagos Islands where they showed proof that one finch had evolved just recently on the big Daphne island. How do you explain this?
Answer by Diane Eager
Since the mid 1970s Princeton University biologists Peter and Rosemary Grant have studied the finches on the island of Daphne Major, and have published two detailed studies of changes in beaks of three finch species that now inhabit the island. The first study covered changes in beak shape and size in the Cactus Finch Geospiza scandens and the Medium Ground Finch Geospiza fortis. The Cactus Finch has a pointed beak and feeds on cactus fruits and pollen. The ground finch has a blunt beak and feeds on seeds. Scientists have long known that the beaks of finches from the same species show variation and are not identical in size or shape. Cactus Finches which have thicker blunter beaks than others of the same species can also feed on seeds when there is no fruit or pollen.
The change that is usually offered as evidence ‘new evolution’ is that the ground finches’ beaks have become smaller and more pointed, while the cactus finch beaks have became blunter, so what has been happening? In 1983 excessively wet weather led to vines and other plants smothering the cacti so there was less cactus pollen and fewer fruits for Cactus Finches, especially those with more pointed beaks. Those with blunter beaks could still eat seeds, so they survived. The loss of cactus food was particularly hard on the female Cactus Finches because males drove them off the cacti. This lead to many females dying which resulted in an imbalance of the sexes, so cactus finch males mated with ground finch females. This hybridisation made for some mixing of genes for beak shape in subsequent generations which explains the continued trend to blunter beaks in cactus finches, and more pointed beaks in the ground finches – each group had inherited genes from the other species. Reference: Science, vol. 296, p707, 26 April 2002.
A second study looked at changes in the Medium Ground Finch Beak from 1973 to 2006. In the late 1970s there was an increase in average beak size, followed by a gradual downward trend back to the 1973 average. The beaks then remained much the same size until a sudden decrease in 2005 – 2006. So again we must ask what has happened?
The Medium Ground Finch mostly eats small seeds, but some birds which have a larger than average beak can eat the large seeds from a plant named Tribulus cistoides (Tc). In 1977 there was a severe drought so there were fewer seeds of all sizes, but birds with larger beaks could eat from plants producing either large or small seeds, so they survived and bred. The next few generations had on average larger beaks. However, in 1982 the Large Ground Finch Geospiza magnirostris moved onto the island. These birds are larger than the Medium Ground Finch, and have a large blunt beak that enable them to eat large seeds. Therefore, they did well on Daphne Major by eating large Tc seeds. But since the drought had ended the smaller beaked medium ground finches had plenty of their preferred smaller food, and did not need to eat large Tc seeds. However, in 2003 there was another drought, but this time Medium Ground Finches could not eat the large Tc seeds because Large Ground Finches had eaten them all. However, any birds with small than average beaks were able to survive on small seeds so the average beak size decreased. (Reference: Science vol 313, p224, 14 July 2006)
Have the birds evolved?
The finches of Daphne Island finches have actually inherited all variations for beak size under discussion and have not produced new and novel previously unknown genes, then they have not evolved. It is important to repeat that all the characteristics being offered as proof of evolution existed before the time of the study, including variations in beak size and shape. It is true that birds with the beak size that could not cope with the harsher environment in times of drought and increased competition have died out, leaving those that could eat available food to survive. Survival of the fittest and natural selection have certainly occurred, and have eliminated the unfit from among existing living things. but these processes have not, and cannot, produce any new living things.
The fact that fertile offspring were produced from the cross breeding from different species indicates the differing finches aren’t very different from one another, and are really one kind. Further evidence that the Galapagos finches are really all one kind comes from research into how the bird’s beaks grow during embryonic development. It has been discovered that the length and thickness of the finch beak is determined by the relative amounts of two biochemicals named CaM and Bmp4. All the finches produce both these chemicals but when a bird makes high levels of CaM and low Bmp4, it results in a long thin beak like a cactus finch, while low amounts of CaM and high Bmp4 results in the short stout beak of the large ground finch. Variations in amounts of these two chemicals are enough to explain all the different beak shapes of all the Galapagos Island finches, not only the birds on Daphne Major. (Reference: Nature, vol. 442, p563, 3 August 2006)
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