Viruses are little more than parasitic fragments of RNA or DNA. Despite this, they are astonishingly abundant in number and genetic diversity. We don’t know how many virus species there are, but there could be trillions.
Human damage to biodiversity is leading us into a pandemic era. The virus that causes COVID-19, for example, is linked to similar viruses in bats, which may have been passed to humans via pangolins or another species.