Seite - 46 - in The Origin of Species

46 ORIGIN OF SPECIES breeds were suddenly produced as perfect and as useful as we now see them ; indeed, in many cases, we know that this has not been their history. The key is man's power of accumu- lative selection : nature gives successive variations ; man adds them up in certain directions useful to him. In this sense he may be said to have made for himself useful breeds. The great power of this principle of selection is not hypo- thetical. It is certain that several of our eminent breeders have, even within a single lifetime, modified to a large extent their breeds of cattle and sheep. In order fully to realise what they have done, it is almost necessary to read several of the many treatises devoted to this subject, and to inspect the animals. Breeders habitually speak of an animal's organi- sation as something plastic, which they can model almost as they please. If I had space I could quote numerous passages to this effect from highly competent authorities. Youatt, who was probably better acquainted with the works of agri- culturists than almost any other individual, and who was him- self a very good judge of animals, speaks of the principle o£ selection as "that which enables the agriculturist, not only to modify the character of his flock, but to change it altogether. It is the magician's wand, by means of which he may summon into life whatever form and mould he pleases." Lord Somer- ville, speaking of what breeders have done for sheep, says :— "It would seem as if they had chalked out upon a wall a form perfect in itself, and then had given it existence." In Sax- ony the importance of the principle of selection in regard to merino sheep is so fully recognised, that men follow it as a trade ; the sheep are placed on a table and are studied, like a picture by a connoisseur ; this is done three times at intervals of months, and the sheep are each time marked and classed, so that the very best may ultimately be selected for breeding. What English breeders have actually effected is proved by the enormous prices given for animals with a good pedigree ; and these have been exported to almost every quarter of the world. The improvement is by no means generally due to crossing different breeds ; all the best breeders are strongly opposed to this practice, except sometimes amongst closely allied sub-breeds. And when a cross has been made, the closest selection is far more indispensable even than in ordi-