The unique quality of the human species
In the Kuttner short story "The Proud Robot," an inventor creates a brilliant robot while he's drunk, and can't remember why. It turns out that for all the robot's skills and beauty of construction, he was built to be a can opener.
Humans have one useful quality that no other species has: if that miles-wide rock heads in our direction from deep space, there is no other species in existence that can save our planet.