Richard Dawkins' (1976) selfish DNA hypothesis (that the only purpose of DNA is to perpetuate itself) is clearly reflected in the case of repetitive DNA, especially retrotransposons. These ubiquitous, self-replicating DNA elements do not seem to do anything but invade the host's genome (Orgel and Crick 1980; Doolittle and Sapienza 1980). Mutations caused by the activity of retrotransposons may eventually be evolutionarily advantageous, but are more likely to be deleterious for the host organism and thus eliminated from the population (Charlesworth et al. 1994). However, insertions of those elements that do not alter any functional region of the genome may be perpetuated in the population
