There may truly be said to be a constant struggle going on between, on the one hand, the tendency to reversion to a less perfect state, as well as an innate tendency to new variations, and, on the other hand, the power of steady selection to keep the breed true.
Benetan esan daiteke etengabeko borroka dagoela honako faktore bi hauen artean, alegia, egoera hobegarriagora bihurtzeko joera, aldakuntza berrietarako sortzetiko joerarekin batera, alde batetik, eta, bestetik, arrazari garbi iraunarazteko hautespen naturalaren eragin iraunkorraren artean.