When organisms diverge from a common ancestor and inherit certain characteristics which become modified by natural selection of mutant phenotypes, it is as if some are traits are locked in place and are unable to change in certain ways.
Cando os organismos diverxen dun antepasado común e herdan certas características que quedan modificadas pola selección natural de fenotipos mutantes, é como se algúns trazos estivesen pechados nunha forma determinada e fosen incapaces de cambiar de certas maneiras.