Retroviruses, a family of viruses that includes HIV, may be almost half a billion years old, possibly older. New genetic analyses of certain retroviruses date their birth several hundred million years earlier than previously believed.

Publishing their findings in Nature Communications, researchers looked to fossils to conduct genetic analyses of endogenous retroviruses, which are retroviruses that incorporate their genetic material into the genome of a living thing; this genetic code is then  passed on to offspring.

The researchers studied the genetic sequences of endogenous retroviruses that resemble what are known as foamy viruses. They found genitic materials of these foamy-like viruses in a diverse array of marine creature fossils, including those of ray-finned fish and amphibians. They used a new type of mathematical model to chart the evolution of such viruses and to make inferences about the origins of the retrovirus family.

The scientists estimated that retroviruses first emerged in the ocean about 450 million years ago, possibly sooner, in the early Paleozoic Era. They then evolved along with the marine life they infected and continued to do so as sea creatures adapted for life on land.

To read a press release about the study, click here.

To read the study, click here.