In Variation, Darwin wanted to expand on this artificial mechanism of evolution beyond examples in Origin, where he describes familiar and tangible results of husbandmen in his argument that selection by the analogous natural means-survival of the fittest-was not just plausible or possible, but probable. Darwin felt that an understanding and appreciation of the depth of artificial selection was fundamental to the acceptance of natural selection. 7).ĭarwin's The Variation of Animals and Plants Under Domestication ( 6) offers a litany of facts and examples of artificial selection in action at the hands of plant and animal breeders. Artificial selection is a conscious, if unintentional, process, and therefore is generally considered to be effected only by humans (but see ref. Although natural selection plays a considerable role in the evolution of many traits (e.g., disease resistance) during the animal domestication process, sexual selection is effectively trumped by the human-imposed arrangements of matings and often by the human desire for particular secondary sexual characters. This often amounts to prezygotic selection (where mates are chosen by humans) versus postzygotic selection (where the most fit progeny reproduce differentially) as in natural selection. Artificial selection, generally the motive force behind domestication, is often equated with selective breeding. Sexual selection is a natural process of intraspecific competition for mating rights.
We perceive today, as did Darwin, that natural selection is the environmentally driven mechanistic process by which more advantageous traits are, on the whole, passed on to succeeding generations more often than less advantageous traits because of differential reproduction of the individuals possessing them. The consequences for the planet (as well as for humanity and its domesticates) have been profound, and have included the complete transformation of almost every natural ecosystem on Earth. However, to date no domestic animal has gone extinct ( 3). The world's species are going extinct at a rate 100–1,000 times faster than the historic “background” rate, primarily as a result of habitat loss, which is itself overwhelmingly driven by conversion of natural habitats to agriculture. Today, 4.93 billion hectares are used for agricultural practices, which also account for 70% of all fresh water consumed ( 2). Agricultural food production ( sensu lato, including animal husbandry) has allowed the human population to grow from an estimated 10 million in the Neolithic to 6.9 billion today, and still expanding ( 1). Exploiting the genetic diversity of living plants and animals for our own benefit gave humans a leading role in the evolutionary process for the first time. It was no more than 12,000 years ago that humankind began to consciously harness the 4-billion-year evolutionary patrimony of life on Earth. That insight seems at first trivial, but reflection reveals just how extraordinary and fundamental artificial selection (manifest as domestication) has been to human success as a species. Eurasian wildcats initiated domestication and their evolution to companion animals was initially a process of natural, rather than artificial, selection over time driven during their sympatry with forbear wildcats.Īrtificial selection is unique in that, as the name suggests, it is wholly unnatural. Wildcat domestication occurred through a self-selective process in which behavioral reproductive isolation evolved as a correlated character of assortative mating coupled to habitat choice for urban environments.
The first domestic cats had limited utility and initiated their domestication among the earliest agricultural Neolithic settlements in the Near East. Those wolves less afraid of humans scavenged nomadic hunting camps and over time developed utility, initially as guards warning of approaching animals or other nomadic bands and soon thereafter as hunters, an attribute tuned by artificial selection. Wolf domestication was initiated late in the Mesolithic when humans were nomadic hunter-gatherers. Two notable exceptions are cats and dogs. Most domesticates have their origin in one of a few historic centers of domestication as farm animals. Artificial selection is the selection of advantageous natural variation for human ends and is the mechanism by which most domestic species evolved.
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