The reason for the 50 years of oil, as I heard it explained, is that this is how far ahead the oil companies plan. They look for enough oil to cover the timeframe they plan for. When they have that covered, they don’t look, until they need more. When they need more, they go and find it.
That’s the case for most species.
As a very specific and highly functional example of critical viral proteins in other organisms, there wouldn’t be any placental mammals without viruses. https://en.m.wikipedia.org/wiki/Placenta