Retroviruses (like HIV) and retrotransposons are collectively called retroelements, as both reproduce within the DNA of an organism. Retrotransposons and retroviruses both contain the gene for reverse transcriptase and both can remain dormant. However, while retroviruses are able to leave the cell and infect a new individual, retrotransposons mainly pass from parent to offspring.
Little is known about retrotransposons and how they cause damage. One retrotransposon called R2 has been in insect DNA for over 500 million years. R2 infects only one particular gene, rendering it useless. Most insects have many copies of this gene, but scientists have observed that insects with lots of R2 elements have slowed growth or die young. Other scientists are surveying a variety of different organisms, including humans, looking for retrotransposons. With this data, they may be able to construct a phylogeny for the element and deduce clues about its evolution. In Drosophila, researchers are studying a retrotransposon called the I factor and have suggested that the I factor causes damage only when too few copies of it exist. Certainly, scientists are no longer taking retrotransposons lightly.
"Retrogrettable Occurrences" The Economist, July 20, 1996