The theory of selfish DNA was born as a throwaway remark in the book "The Selfish Gene" by Richard Dawkins, when he pondered why there is so much surplus DNA in the genomes of some animals and plants.

Perhaps, he suggested, our genomes are riddled with digital parasites, sequences of code that proliferate at our expense and aren't there to help "us"—that is, the organism as a whole—at all.

This...