I just wanted to add that I probably was exaggerating when I said "we have no idea how that happened." re: VP40, bats, and ebola.

Best guess is: a retrovirus and an ebola-like virus infected a bat cell at the same time, the retrovirus accidentally picked up some of the bat genome, which then somehow recombined with the negative sense RNA genome of the ebola-like virus. We have no proof this happened like this, but it's the best guess.

Just as an example of the crazy things that we think probably happen in the world of viruses in nature.