Barriers that Keep Different Species from Interbreeding

What keeps members of two related species from mating with each other? There are many different reproductive barriers. Species might not interbreed simply because their mating or flowering seasons don’t overlap. Some corals, for example, reproduce only one night a year, spewing out masses of eggs and sperm into the sea over a several-hour period. Closely related species living in the same area remain distinct because their peak spawning periods are several hours apart, preventing eggs of on...

 Examples of Species Evolved through Human Artificial Sele...

The dog can stand for the success of other breeding programs. As Darwin noted in The Origin, “Breeders habitually speak of an animal’s organization as something quite plastic, which they can model almost as they please.” Cows, sheep, pigs, flowers, vegetables, and so on—all came from humans choosing variants present in wild ancestors, or variants that arose by mutation during domestication. Through selection, the svelte wild turkey has become our docile, meaty, and virtually tasteless...

 Dogs are Evolved from Wolves Through Artificial Selection

Take the domestic dog (Canis lupus familiaris), a single species that comes in all shapes, sizes, colors, and temperaments. Every single one, purebred or mutt, descends from a single ancestral species—most likely the Eurasian gray wolf—that humans began to select about 10,000 years ago. The American Kennel Club recognizes 150 different breeds, and you’ve seen many of them: the tiny, nervous Chihuahua, perhaps bred as a food animal by the Toltec of Mexico; the robust Saint Bernard, thick...

 Dog Breeding and Evolution

Another familiar example is the sculpting of the wolf, Canis lupus, into the two hundred or so breeds of dog, Canis familiaris, that are recognized as separate by the UK Kennel Club, and the larger number of breeds that are genetically isolated from one another by the apartheid-like rules of pedigree breeding. Incidentally, the wild ancestor of all domestic dogs really does seem to be the wolf and only the wolf... [...] The main point I want to draw out of domestication is its astonishing ...