No. 34: Jul-Aug 1984
It was a surprise when DNA sequences from mitochondria in yeast cells were discovered setting up shop in the nuclear genomes (i.e., the normal genetic endowment of the cell nucleus). Now biologists find that DNA sequences in many species regularly and frequently hop from one genome to another. Genetic material from cell chloroplasts mix with that of the mitochondria and that of the normal nucleus in what seems to be a free-for-all. This genome hopping has earned DNA the adjective "promiscuous."
The significance of DNA promiscuity is to be found in the general belief that the cell's mitochondria and chloroplasts were once independent biological entities that, in the course of life's development, invaded or were captured by cells and have led a symbiotic life ever since. The mitochondria and chloroplasts perform certain important functions in the cell but were thought, until now, to retain considerable genetic independence.
(Lewin, Roger; "No Genome Barriers to Promiscuous DNA," Science, 224:970, 1984.)
Comment. The promiscuity of DNA raises speculation that other DNA-bearing entities that invade the body, especially the viruses, may transfer their DNA to the host, and conceivably vice versa. With DNA apparently much more promiscuous than believed earlier, the role of disease in the development of life takes on a new importance. In other words, all species can potentially exchange genetic information with all others. In fact, in a broad sense, sperm are infectious agents, and pregnancy a disease! DNA will stop at nothing to spread itself around.