The Viruses That Made Us Human

Viruses give us infections, from the common cold to Ebola and Aids. But new research shows that they may also have played a key role in shaping the evolution of homo sapiens.

- Kat Arney

ZIKA, Ebola, flu, even the boring old common cold – we’re all familiar with the viruses that plague humanity. But while we know they make us sick, it may be surprising to discover that, over millions of years, we’ve managed to harness and domesticate these crafty invaders. From the earliest stages of life to the smiles on our faces, viruses have had a huge influence on our human species.

Viruses are little more than a string of genes (usually in the form of a molecule called RNA) packaged in a protein coat, and they all work in the same basic way. Once a virus has infected a cell, it hijacks the cell’s own molecular machinery to copy its genes and churn out viral proteins. New viruses are assembled from these freshly-manufactured parts, which eventually burst out in search of new cells to attack.

For most viruses, such as flu, the story ends there. But a handful of retroviruses – including HIV – are even sneakier, smuggling their way into our DNA. They insert themselves randomly into the genome of an organism, lying low until the time is right to start virus production again. But once a retrovirus has got into an organism’s DNA, there’s no guarantee that it will stay put. The genetic instructions can be ‘read’ from the embedded virus, converted into DNA and then pasted into another location in the genome. Repeat this cycle again and again, and multiple copies of the viral DNA quickly build up.