Chapter One
In which Darwin uses examples from domestication to explore the causes of variability and the principles of selection
Farmers have been unwitting evolutionists since they began, as they have shaped the characteristics of domesticated species. Nowhere is the power of human selection more clearly seen than by the fireside. Dogs were domesticated around 16,000 years ago in China, perhaps for meat. Their ancestors were wolves 鈥� and the two still share the same scientific name, Canis lupus 鈥� but dogs have changed mightily since then. The breeders were ruthless, killing off the animals of which they did not approve. This selective death, combined with selective sex, soon subdivided dogs into a huge variety of forms.
Some kinds have been distinct for centuries but most are less than 400 years old. In Darwin鈥檚 childhood there were no more than 15 designated breeds. By the time The Origin was published, the number had risen to 50. It is now around 400. Many of today鈥檚 varieties have gained a distinct identity in no more than 30 or so canine generations. Sometimes a single mutation sparks a new variety.
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The Irish wolfhound stands a metre high and weighs as much as 30 chihuahuas, but the difference in size between the two is due to a single gene, which comes in one form in the large animal and another in the small. Most divergence between breeds, however, involves many genes, unwittingly selected by breeders aiming to refine the characteristics of particular lineages. Were the various breeds of dog to run wild, they might be classified by an enthusiastic but naive naturalist as separate species. How could a dobermann possibly belong in the same category as a chihuahua?
Even so, in spite of some logistical difficulties with sex, crosses among dog breeds produce fertile offspring, which is one of the several definitions of what a species is. In the same way, the European grey wolf crosses freely with domestic dogs, which is why it shares its name. The pedigree dog clubs have laid out the case for Darwinism in a few short decades.
Read more: On the Origin of Species, Revisited