Arthur C. Clarke - The Possessed
Channel: omennoecile
Date: 2011-09-18

Dynamic Science Fiction 1953

It also is a parasite, it lives off other intelligent beings, by colonizing their minds. 
But this is primeval earth. Where there is life aplenty, there is no sign of anything intelligent. Should it nudge some of the living beings towards becoming intelligent, or roam the universe in search of another suitable world. 

Fantastic story.