Un-rooted phylogenies, estimated from a reverse transcriptase protein alignment. |
Retroviruses are enough to induce extreme denialism in creationists because they can't be explained in terms of intelligent (sic) design, or design of any sort, but they can easily be explained by standard genetic evolutionary theory. In fact, they can only be explained by evolution.
Retroviruses are a class of related RNA viruses which, on gaining entry to a host cell, insert the DNA counterpart of their RNA into the genome, making themselves practically invisible to the normal antibody defences of the host. They can lay dormant for many years before being activated and, if they infect the germ-line cells, can be passed on to the next generation.