All that has happened is the 'heightening' of certain features already in the parents. In addition, whilst polyploidy has been of great value to humans in the production of better plants and cereals, cases of polyploidy in animals is confined mainly to a few worms, insects etc. It has played no significant part in the evolution of the animal kingdom. We have now to ask whether such jumps could occur in no more than a few thousand generations through the operation of 'orthodox' biological processes. There are two possibilities, polyploidy and tandem gene duplication, which we shall begin this chapter by considering.
Polyploidy consists of a duplication of the entire genome.
But for animals with distinct sexes a polyploidal individual without a polyploidal mate is doomed to sterility. Occasionally the enzymes that copy DNA may copy twice over a length of DNA containing a particular gene. If this happens during the production of a sperm or ovum, an individual with two copies of the gene side by side, in tandem, may come to be born, the two copies being contained not only in the sex cells of the new individual but in all its body cells. If, moreover, it happens that the gene in question produces a protein which the species could well benefit from having more of, the new individual with a double dose of the protein will have an advantage over other single-gene individuals and so the double gene will tend to spread itself by natural selection. Even if the double gene conveys no particular advantage it may still spread by random effects, provided it conveys no disadvantage either, especially if the breeding group to which the individual belongs is small.