Freeman Dyson is still alive, so the essay is still in copyright. But much of the essay is made up of two sources, from H. G. Wells and Robinson Jeffers, so I'll quote them (more fully than I did before) here - Wells is in the public domain, Jeffers will be in five years (but, fair use).
Do not misunderstand me when I speak of the greatness of human destiny. If I may speak quite openly to you, I will confess that, considered as a final product, I do not think very much of myself or (saving your presence) my fellow creatures. I do not think I could possibly join in the worship of humanity with any gravity or sincerity.
Think of it. Think of the positive facts. There are surely moods for all of us when one can feel Swift's amazement that such a being should deal in pride. There are moods when one can join in the laughter of Democritus; and they would come oftener were not the spectacle of human littleness so abundantly shot with pain.
But it is not only with pain that the world is shot — it is shot with promise. Small as our vanity and carnality makes us, there has been a day of still smaller things. It is the long ascent of the past that gives the lie to our despair. We know now that all the blood and passion of our life was represented in the Carboniferous time by something — something, perhaps, cold-blooded and with a clammy skin, that lurked between air and water, and fled before the giant amphibia of those days. For all the folly, blindness and pain of our lives, we have come some way from that. And the distance we have traveled gives us some earnest of the way we have yet to go.
It is possible to believe that all the past is but the beginning of a beginning, and that all that is and has been is but the twilight of the dawn. It is possible to believe that all the human mind has ever accomplished is but the dream before the awakening. We cannot see, there is no need for us to see, what this world will be like when the day has fully come. We are creatures of the twilight. But it is out of our race and lineage that minds will spring, that will reach back to us in our littleness to know us better than we know ourselves, and that will reach forward fearlessly to comprehend this future that defeats our eyes.
All this world is heavy with the promise of greater things, and a day will come, one day in the unending succession of days, when beings, beings who are now latent in our thoughts and hidden in our loins, shall stand upon this earth as one stands upon a footstool, and shall laugh and reach out their hands amidst the stars.
names foul in the mouthing.
The human race is bound to defile, I've often noticed it,
Whatever they can reach or name. They'd shit on the morning star
if they could reach...
The awful power that feeds the life of the stars has been tricked down
into the common stews and shambles...
A day will come when the earth will scratch herself and smile
and rub off humanity.