what? if life was on mars, both of those things would be irrelevant. AND neither one of them says anything about hostility
He's not talking about hostility. He's talking about the Great Filter.
If we find life on Mars (that evolved entirely independently from life on Earth), then that reinforces the Fermi Paradox.
It means life starting on other planets is highly probable. It would have to be for two neighbouring planets in the same system to have developed life independently of each other.
So if it is so probable that life will come about out in the galaxy/universe, then given the age of the universe and how many stars/planets there are (in our galaxy alone), then how come we can't see signs of life out there, particularly intelligent life (like ourselves).
It means one of two things;
1) We're not looking properly or the life out there doesn't want to let people know it's here, or...
2) There's some high probability that means life doesn't develop to be intelligent enough to create a sign of itself. This high-probability, is the Great Filter, because whatever it is it filters out life.
At the moment we only know of ourselves as intelligent life, and our planet as supporting any type of life.
Therefore we have no idea if this Great Filter (if it exists) existed in our past or is it in our future.
It could be that it was something we overcome in our past. That it's improbable that life will develop to be single-celled, or multi-celled, or to reach further and develop sentience.
Or, it means that most life in the universe is destroyed, or fails to develop enough to leave a trace of itself in the cosmos.
If it's the former and we find life on mars that is equal or less inteligent than us, whether it were sentient species, simple animals, bacteria, or just amino acids, then it suggests that the easy part of developing intelligent life is the start of it. These stages.
So we can assume that all the life that should be out there, given how big the universe is, had no real difficulty starting as amino acids, or developing cellular life, or becoming sentient.
But we still can't find other life. So presumably the hard part comes after our current stage.
It must be probably that life out there regularly destroys itself by this stage, or simply finds itself lacking the resources to travel the galaxy or leave signs of existence behind.
Which means we should anticipate the same sort of things happening to us.
We can come to the assumption (although not guarantee), that humanity is doomed. Either to wipe itself out, or be wiped out by natural disaster, or to not achieve the means to leave our solar system or broadcast out into the cosmos.
We might never find intelligent life out there.
Basically, the absolute best sort of life we can find would be intelligent life.
Finding intelligent life out there suggests that we've overcome the difficult part of evolution.
Finding simple life suggests life is pretty common, but it doesn't have much luck surviving longer than we have.