The Sentos were born in a unique manner. Unlike most creatures, they didn't evolve naturally from the cell stage. Instead, they were created when the above mentioned scientists made an error in a nuclear research facility. The resulting explosion bonded organic molecules together, which resulted in the birth of a handicapped creature, the Sentos. This handicap was size-based, so, when placed in the different enviroments, none of the evolved species grew much over 3 feet with the exception of the Nexo-herbinel.