Selective breeding is used by dog breeders, as well as breeders of horses, cows and other livestock. As its name implies, breeders who are looking for a particular characteristic in an animal will select only those animals with that characteristic for breeding. Racehorses and Greyhounds are selectively bred for speed. An American male horse that wins the Kentucky Derby, or even better the Triple Crown, is assured of a lifetime of enormous stud fees as hopeful race competitors bring their fastest Dams to them for breeding.
The development of certain dog breeds through selective breeding follows the same pattern. Today’s Collie dog is an example of selective breeding for a particular head type. The Collie familiar to us today bears little resemblance to the Collie of one hundred years ago. The German Shepherd Dog appeared one hundred years ago in Germany as a result of the selective breeding of the best herding dogs available. Dogs (both males and females) were selected for breeding because of their superior ability to herd sheep. Pit Bulls were bred to grab hold and not let go in a dog fight. Bull Dogs were selectively bred for their ability to control bulls.
All the sporting dogs, hounds, working dogs and herding dogs listed in the national breed clubs were selectively bred for a particular job. Scent hounds were bred to have extremely sensitive noses for scenting prey for hunting. Sight hounds were selectively bred for their ability to spot moving prey at a distance.
Selective breeding was used by farmers long before anyone understood the principles of genetics. Through trial and error, they found that when they bred the best of their stock to the best, not only did they produce better stock, but there was greater consistency in what their stock were producing.
Not all selective breeding produces happy results. The Rhodesian Ridgeback, highly prized for the distinctive color down its backbone, is also subject to back problems that do not seem exist in the Ridgebacks without that coloration.
Every time a breeder deliberately mates two animals, selective breeding is the result whether the breeder is aware of it or not. For this reason, responsible breeders have an ethical duty to try to improve the breed with every breeding rather than simply putting two possibly defective dogs together that produce defective pups.
What then is natural selection and how does it differ from selective breeding? Natural selection is just what its name implies: certain breeds or strains of animals have developed naturally over time. The ancestor of the horse was a very small animal. The horse evolved (changed) over time simply by the process of survival. Certain horses had a greater ability to live long enough to produce offspring. If these offspring also lived long enough to produce offspring, a particular strain of horses developed that was better adapted to the environment in which it lived because it was able to live longer than other horses. Over time, through this process of natural selection, certain horses thrived and lived longer.
There is an hypothesis that domesticated dogs, themselves, are a product of natural selection. If we accept the idea that dogs are the descendants of wolves, how did they become dogs? Wolves became dogs through the process of natural selection first, followed by the process of selective breeding.
There is speculation that wolves discovered that humans were a source of food. The campsites of small bands of humans looking for food always left behind unused scraps and human feces. From scavenging for food after a human troupe had moved on, to approaching the troupe before they moved on, not close but nearby, took a long time. Humans probably discovered, before very long, that wolves could alert them to the approach of strangers or game.
Finding the wolves useful, humans may have begun deliberately leaving food out to keep them nearby. As some wolves lost their fear of humans, and became attached to camps, the beginnings of natural selection appeared. Certain wolves adapted better than others, certain wolves had valued characteristics, others traded in their freedom for food. It is not known just how wolves became domesticated into dogs, but it did eventually happen.
Many dog breeds have evolved through natural selection rather than selective breeding.
and the South African wild dog are the best known. They remain wild rather than domesticated but they are definitely a recognizable breed of dog rather than a breed of wolves.
Natural selection created dogs but selective breeding practices created different types of dogs for human use and pleasure. The time required to create a new dog breed through natural selection probably takes hundreds of years. To create a new dog breed by selective breeding takes only one breeding. (Note the Cockapoo (Cocker/Poodle mix) and the Labradoodle (Labrador Retriever/Poodle mix).
Natural selection and selective breeding have one thing in common: they establish permanent genetic codes in which all offspring breed consistently and true. Selecting breeding stock with the desired characteristic, will solidify the genetic DNA. Random breeding practices produce a mixed bag of genes.