The Gene Bombs are deadly bombs designed and used by the Xorda, and they are capable of causing the devolution of any species on any planet the Xorda race attacks. The Gene Bombs were used during the Xorda's attack on Earth which resulted in the devolution of the human race into the four-fingered Overlander species (although it was apparently supposed to devolve humans much further back, to pre-intelligence). It also resulted in the rapid evolution of the animal kingdom, blending their DNA with that of humans to form the Mobian species.