Viral relics have shown that, throughout history, we have been exposed to fewer blood-borne viruses than other mammals.
Our genetic code contains DNA from endogenous retroviruses (ERV) that infected the gametes of our ancestors millions of years ago and have since been passed on from generation to generation. The incorporated genome of these ERVs is known as viral fossils.
Even though such viral relics could cause cancer in other animals, they seem to be benign in humans. A group of researchers from University of Oxford, Plymouth University, and the Aaron Diamond AIDS Research Centre in the USA, set out to find why.
They compared the genetic signature of the two edges of viruses. These edges are supposed to have identical nucleotide sequences but with every generation they underwent different random mutations. By inspecting the divergence between the two edges, it is possible to measure how long a virus has been part of the host’s genome.
It was thus discovered that apes have acquired significantly fewer ERVs over the last 10 million years in comparison to other animals that participated in the study, including dolphins and giant pandas. Furthermore, no new viral DNA has been incorporated in human genome for the last 30 million years. The group of researchers attributed this to a change in behaviour: “As we evolved to use tools as weapons, we began eluding direct contact with infected meat and blood.”
However, lead researcher Dr Magiorkinis from Oxford University remarked: “‘We have shown in the past that Hepatitis C, a virus transmitted mainly through blood, was spread massively after World War II. There is no doubt that the past trend of reduced blood contacts has been reversed in the last century, and this has severe consequences for viral infections.”