Here's a twist on evolution. It may or may not hold up to
Mass extinction seems crucial--ultimately--to the founding of
a greater diversity and adaptability in the post-extinction era.
So it might not be such a bad thing (in the long run) if a huge
comet or series of planetesemal impacts comes along to decimate
75% of this biosphere's species. After the impact, there would
be, say, 2 times the number of species as before the
catastrophe. With more ecological niches being filled in
(arguably) more interesting ways, the need for any given
species to adapt behaviorally is more pressing. And so
behaviors and the underlying neurological mechanisms become
more complex. This is how intelligence evolves.