Extinctionism

Extinctionisim is the act of causing every creature in the game of Nethack to become extinct. A creature is extinct when 120 of it's kind have been born.

How to extinct creatures
A creature is extinct when 120 of it's kind are born. The creatures do not have to be killed in order to be extinct. Once extinct, a creature will never be randomly generated again.

Therefore, you can extinct a creature simply by summoning, or reverse-genociding 120 of it's kind. Killing it is optional, but highly reccomended.

To extinct a creature, you must create it in a way that respects extinction.

Actions that respect extinction

 * Reverse-genociding a monster.
 * Casting create monster via spell, scroll or wand.
 * Waiting around on a level for it to be randomly generated.
 * Entering a level containing a special room such as a zoo, or beehive.