What do you mean by "other 3 souls"? There are six soul types (flight, light, night, sight, might, and fright). Light souls are dropped by enemies in the underground hollow. Night souls are dropped by enemies in the underground corruption/crimson. Sight, might, and fright souls are dropped by hardmode bosses.
By Evolution, I mean Evolution. As in "I look different from my parents because of evolution" ~OrangeWizard