Species inheriting nearly the same constitution from a common parent, and exposed to similar influences, naturally tend to present analogous variations, or these same species may occasionally revert to some of the characters of their ancient progenitors.
Guraso komun batengandik ia osaera berdina heredatu duten eta eragin berdintsuen mende dauden espezieek berezko joera dute aldakuntza analogoak izatera, edo batzuetan beren arbasoen ezaugarrietako batzuetara gibela daitezke.