Natural Selection: A Filter
Natural selection as a principle acting in nature was known before Darwin presented his On the Origin of Species. Before Darwin natural selection was seen as a conservative force, a filter which preserved. Today natural selection is often referred to as a creative force. The reality of the theory is that mutation is the creative force in evolution with natural selection acting solely as a filter for beneficial mutations. For the special creationist mutation is a destructive force with natural selection acting as a preservative filter.
When Darwin introduced the idea of natural selection he did so by referring to the variation available in domesticated varieties of pigeon, dogs, and cattle. From his perspective he believed the variability to be infinite with artificial selection providing an enhanced view of what natural selection was capable of. Over the years artificial selection has instead shown that there are definite limits to selection whether artificial or natural.
In his book The Neck of the Giraffe Francis Hitching points out that with all of the artificial breeding selection practiced by men dogs remain dogs, wheat remains wheat, fruit flies remain fruit flies, and E. coli bacteria remain E. Coli bacteria. This is significant because each of these have shown considerable variability.
The variability in dogs has come under increasing scrutiny as Kennel Club dog breeding programs show the definite limits of variability. Specialized breeds are showing increasing signs of genetic degradation, even in the two hundred or so years since the formation of the Kennel Club, changes have occurred in the breeds that can be shown to be detrimental to the health not only of the individual animals but also of the individual breeds. Otherwise recessive genes have been highlighted in ways making deadly diseases more common in dogs.
Working dogs and mongrels do not show this degradation. As dogs are widely accepted as being descended from the Grey Wolf (to the point that they can still interbreed with wolves) it needs to be said that wolves do not show the variation seen in dogs. In the time since dogs have descended from wolves, wolves have remained wolves.
Dogs vary considerably in size, from Toy varieties that can fit in a shoe to the Great Danes and Wolfhounds that are larger than small horses. For all their size differences though they remain dogs and we appear to have reached the limits of those sizes. Size is limited by genetics, there is a big beyond which dogs can get no bigger and a small beyond which they can get no smaller. They vary widely in behaviour, there are hunting dogs that point at their prey, hunting dogs that retrieve prey, hunting dogs that chase prey, and they remain dogs that are capable of interbreeding with each other. There are varieties of colours, of lengths of hair and even hairless, of types or ears and tails, but they remain dogs.
In a TV documentary (Dogs Decoded) the work of Russian scientists with foxes was highlighted. The Russians wanted to see if they could breed dog-like foxes. As far as is known dogs and foxes cannot interbreed (there are anecdotal accounts but these have not been verified and are disputed on genetic grounds). The scientists chose the most dog-like of captive silver foxes to breed. After only three generations they had succeeded. They had bred foxes that were dog-like in behaviour and were beginning to show dog-like physical characteristics. For all this foxes in the wild do not appear to be becoming dog-like. Natural selection both with wolves and foxes limit’s the expression of this variability although it does genetically exist.
In foxes and wolves what does appear is not a slow increase in variability but a genetic homeostasis. In a National Geographic documentary on cats (The Science of Cats) scientists looking for the origin of the domesticated cat looked for the greatest genetic diversity to identify the oldest population of cats. From what we’ve been taught about Darwinism it might be supposed that the greatest genetic diversity would be found in the youngest population. What is observed, however, is that wild populations tend to preserve the greatest genetic diversity maintaining variability in the genome but preserving a static phenotype.
This is seen also in plants and is the reason why seed banks have been developed. Domesticated plants show a decreased resistance to disease and older varieties are required for crossbreeding to safeguard future use of the domesticated plants, to protect against a loss of genetic information. Rather than new information being created all the time specialized breeding reduces the amount of genetic information available.
The peppered moth is one of the icons of evolution. It has been widely taught (and still is) that the variation in colour of peppered moths during the Industrial Revolution was a prime example of evolution in action. In her book Of Moths and Men Judith Hooper indicated that not only was the experiment flawed (some would claim fraudulent) but in other areas of the world (France and the United States) there was no such variation. What is more, some of the later observations showed the opposite was happening, dark moth populations increased on white surfaces. There was no direct correlation between the colour of the moth, lichen, and the change in population frequency.
The most telling of all the arguments against peppered moths as being an icon of evolution comes from Francis Hitching, “The peppered moth, after all, stayed from beginning to end Biston betularia. ” The peppered moth stayed the peppered moth. From beginning to end both the light coloured and dark coloured interbred and still interbreed. A small change in the population has been extrapolated to indicate the possibilities of large change.
The industrial melanism that occurred in the peppered moth is what some refer to as micro-evolution. These are small changes in a population. Industrial melanism occurs in over 100 species, moths, birds, beetles and cats, yet for some reason none of those others can be represented as showing evolution. There are a variety of reasons why industrial melanism occurs, but only the peppered moth is thought to be an example of Darwinian evolution. Using industrial melanism in the peppered moth is an example of extrapolation. From a small change we suppose a much bigger change.
Michael Denton in his book, Evolution: A Theory in Crisis devotes a considerable portion of one chapter to the problems of extrapolation. From weather we cannot extrapolate climate, they are affected by different forces. From erosion we cannot extrapolate geology, the magnitude of forces involved in geology goes far beyond erosion. From a sentence we cannot extrapolate a book, an article, or even a paragraph.
The rules that govern the behaviour of a sentence are not the same as those that govern the paragraph or article. In the same way the rules that govern genes do not necessarily apply to the rules that govern creatures and populations of creatures. Extrapolation has its limits, what works on a small scale does not necessarily work on a large scale. Put another way, what works for micro-evolution will not necessarily work for macro-evolution. “…there is the depressing precedent, as the history of science testifies, that over and over again theories which were thought to be generally valid at the time proved eventually to be valid only in a restricted sphere.” This appears to be the case with Natural Selection.
- Mutant parade purebred dogs
Purebred dogs are not examples of evolution but devolution; artificial selection culled much genetic information
- Documentary - BBC - Pedigree Dogs Exposed Video by bordercollie19 - Myspace Video
An examination of the results of dog breeding practices in Britain. WARNING! Animal lovers may find this disturbing.