In Weismann's opinion the largely random process of mutation, which must occur in the gametes (or stem cells that make them) is the only source of change for natural selection to work on.
Na opinión de Weismann o proceso en gran medida aleatorio da mutación, que debe ocorrer nos gametos (ou nas células troncais que as formaron) é a única fonte de cambio para que actúe a selección natural.