[Neuromancer]

As to the apparent conservation of the Ebola virus genome over time, the most viable explanation is that the virus circulates in an ecological niche in a host without a mammalian-type immune system, therefore there is very little selection for change.

And recall: the sequences that haven't changed are of the order of a few hundred bases, which is a bit little to go basing a whole new polymerase specificity on.

Perhaps Ebola is in a natural reservoir host in which there is very little selective pressure - perhaps due to its being an insect (or even a plant...?)

Just my $0.02 worth, who knows...