Pleiotropic Effect, The

On the left can be seen normal development in a domestic chicken, and on the right, the harmful effects caused by a pleiotropic gene mutation. Close inspection shows that a mutation in a single gene can damage several organs at the same time. Even if we were to admit that mutations did have a positive effect, the pleiotropic effect would eliminate this advantage by damaging several different organs at once.

One of the proofs that mutations inflict only harm on living things is the coding of the genetic code. In developed animals, almost all the known genes contain more than one piece of information about that organism. For example, a single gene may control both height and eye color.

The effects of genes on development are often surprisingly diverse. In the house mouse, nearly every coat-colour gene has some effect on body size. Out of seventeen X-ray-induced eye colour mutations in the fruit fly Drosophila melanogaster, fourteen affected the shape of the sex organs of the female, a characteristic that one would have thought was quite unrelated to eye colour. Almost every gene that has been studied in higher organisms has been found to effect more than one organ system, a multiple effect which is known as pleiotropy. As Mayr argues in Population, Species and Evolution: "It is doubtful whether any genes that are not pleiotropic exist in higher organisms."186

Due to this characteristic in living things' genes, any defect occurring in any gene in the DNA as a result of a chance mutation will affect more than one organ. Thus the mutation will have more than one destructive effect. Even if one of these effects is hypothesized to be beneficial, as the result of an extremely rare coincidence, the other effects' inevitable damage will cancel out any advantage. (See Mutation: An Imaginary Mechanism.)

Therefore, it is impossible for living things to have undergone evolution, because no mechanism exists that can cause them to evolve.

186. Ibid, p. 149.