What you’ll learn to do: Identify different viruses and the methods they use to infect humans

Viruses are diverse entities. They vary in their structure, their replication methods, and in their target hosts. Nearly all forms of life—from bacteria and archaea to eukaryotes such as plants, animals, and fungi—have viruses that infect them. While most biological diversity can be understood through evolutionary history, such as how species have adapted to conditions and environments, much about virus origins and evolution remains unknown.

While viruses technically aren’t living things (they don’t have cells), they still have DNA or RNA. In this section, we’ll learn how viruses reproduce. As we do, you can compare viral replication to DNA replication in living things.