3. Even if Life is abundant in the Galaxy, plant and animal life is rare. Take our planet as an example:
Plus, it took a long long long long long time for plant and animal life to come about
. Also notice that plant and animal life occurred after a series of unlikely events. And, on top of all this, human life and other intelligent life is even rarer. Even if you take Earth as a model of a planet that exists throughout the galaxy we are still most likely alone.