Many genes have unrelated intein-coding segments inserted at different positions. For these and other reasons, inteins (or more properly, the gene segments coding for inteins) are sometimes called "selfish genetic elements", but it may be more accurate to call them parasitic. According to the gene centered view of evolution, most genes are "selfish" only insofar as to compete with other genes or alleles but usually they fulfill a function for the organisms, whereas "parasitic genetic elements", at least initially, do not make a positive contribution to the fitness of the organism.