I am guessing it varies from virus to virus, but I think it has been proven that it is nearly impossible for a virus to "jump" from one mammal species to another. At least, that seems to especially be the case with COVID-19. If viruses could generally just jump from any live or dead mammal or bird to any other mammal, bird, including humans - it seems we'd be done long ago.
This is why the "wet market from a bat" theory doesn't hold up well - at all. The first cases were found to be not close really to any wet market anyway, instead very close to the Wuhan virology lab, found in workers who frequented the lab. And...
that is what the whole "gain of function" definition is all about: dangerous genetic engineering via human intervention, to enable other-mammal-based viruses to "gain the functionality" to be able to infect human species. Why we would ever want to do this genetic tampering exercise, as a human race, at all, let alone in a reckless risky dangerous out-of-control Wuhan lab, and US help fund it, is impossible to justify.
The Wuhan lab should be shut down tomorrow. And US should demand refund of any funding of the lab from China. Just for starters. China should be required to pay significantly more $ for their reckless mismanagement of the labs, if it can be proven that the Wuhan lab is the origin. There at least needs to be a real investigation, by people other than CCP, WHO.... as to the root cause, origin of the COVID outbreak