Scientists are different from most resources, as they are returned to the player after each use. The only way to lose a Scientist is by resetting the research tree of the Dark Matter Institute (if the Doppelganger technology has been purchased).
The player starts the game with one Scientist. New Scientists can be bought for Diamonds and one additional Scientist can be earned by researching the Doppelganger technology in the Dark Matter Institute. There is no limit to how many Scientists a player can have, but each consecutive purchase of a Scientist increases its price.
Scientists are required in the Research Labs to produce resources, evolve Bacteria, irradiate Evolved Bacteria and Bacteria colonies, clean the lab after Bacteria mutation, etc. After researching the Quantum Leap technology at the Dark Matter Institute, each idle Scientist also doubles the player's BPS.