But why, in the case of distinct species, the sexual elements should so generally have become more or less modified, leading to their mutual infertility, we do not know; but it seems to stand in some close relation to species having been exposed for long periods of time to nearly uniform conditions of life.
Dimorfismoari buruzko egitateak, baita elkarrekiko gurutzaketen emaitzak ere, gogoan hartzeak argiro garamatza ondorio hauxe ateratzera, alegia, gurutzaturiko espezieen antzutasunaren oinarrizko kausa haien sexu-elementuen ezberdintasunetara mugatzen dela.