There are numerous theories of how viruses emerged. Some scientists say they formed from stray bits of genetic material that learned to move between cells. Others think they descended from once-autonomous organisms, but over time they chose to embrace a parasitic way of life. Some have even suggested that they were our progenitors, and that all of us are descended from some virus-like ancestor. Because they're made up of mere strands of proteins that unfortunately leave no trace in the archeological record, it's impossible to study a 'virus fossil." But fortunately, their traces can be found in the genomes of other living beings. Researchers have detected traces of viruses in a wide range of organic genetic material, even in our own human genome - around 8 per cent of our own DNA (100,000 pieces) is viral.

— Unseen Beings by Erik Jampa Andersson (16%)