Virus-first hypothesis: Viruses evolved from complex molecules of protein and nucleic acid before cells first appeared on earth. By this hypothesis, viruses contributed to the rise of cellular life.

What came first cells or viruses?

Viruses did not evolve first, they found. Instead, viruses and bacteria both descended from an ancient cellular life form. But while – like humans – bacteria evolved to become more complex, viruses became simpler. Today, viruses are so small and simple, they can't even replicate on their own.

Are viruses older than cells?

Forterre suggests that viruses evolved after primitive cells but before modern cells. Some of the viruses that infect the three different domains of life share several of the same proteins, suggesting that they may have evolved before life diverged into these three branches.