The explanation is to a large extent simple, on the theory of the selection of successive slight modifications, each being profitable in some way to the modified form, but often affecting by correlation other parts of the organisation.
Azalpen aski xumea du, ordea, hein handian hurrenez hurreneko eraldaketa arinen hautespenaren teorian oinarrituz: eraldaketa bakoitza forma eraldatuari berari nolabait onuragarri zaiolako, baina organismoaren beste atal batzuei ere sarri korrelazioz ukitzen dielako.