- The SARS-CoV-2 virus shares a most recent common ancestor with a bat coronavirus, implying that somehow it jumped the species barrier to infect humans
- Viruses circulating in animals sometimes jump species boundaries to infect humans
- This requires mutations that allow the virus to both establish (ie replicate) in a human cell and transmit, often through the air
- So-called 'zoonotic' infections (coming from animals) that can then be transmitted among humans are usually rare because multiple mutations are required, and the chances that all the mutations required to establish and replicate in a novel host is usually very small
- But it does happen occasionally, and can be made to happen in the lab, as demonstrated in this paper that showed just five mutations were required for transmission through the air