https://phys.org/news/2018-07-genetic-parasites-natural-billions-years.html

In a new study published in EPL, researchers Jaime Iranzo and Eugene V. Koonin at the National Institutes of Health in Bethesda, Maryland, have found that horizontal gene transfer may be one of the keys to understanding the persistence and spread of genetic parasites over evolutionary timescales.

In horizontal gene transfer (HGT), genetic information is transferred to an organism by a variety of mechanisms other than the traditional parent-to-offspring process of transferring DNA. For example, an organism may receive genetic material directly from another organism—even one of a different species—or pick up genetic material from the surrounding environment. For genetic parasites, HGT offers a way to infect new hosts, providing a potential mechanism to compensate for the losses due to natural selection.