Darwin famously first described natural selection in 1859 with his classic monograph On the Origin of Species. Sexual selection was addressed in Descent of Man, and Selection Related to Sex in 1871. In between those two, in 1868, Darwin published a 2-volume work, The Variation of Animals and Plants Under Domestication, in which he expands upon a third distinct stream of evolutionary mechanism—artificial selection—that he first had outlined in Origin.
Artificial selection is unique in that, as the name suggests, it is wholly unnatural. 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. 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. 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. 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 (Groube, 1996). Today, 4.93 billion hectares are used for agricultural practices, which also account for 70% of all freshwater consumed (World Resources Institute, 2000). 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. However, to date no domestic animal has gone extinct (Zeder, 2008). 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.
Domesticating animals and plants brought surpluses of calories and nutrients and ushered in the Neolithic Revolution. However, the Neolithic Revolution involved more than simple food production; it was also the growth of an agricultural economy encompassing a package of plant and animal utilization that allowed for the development of urban life and a suite of innovations encompassing most of what we today think of as culture (Bar-Yosef, 1998; Peters et al., 2005). Much of modernity is an indirect consequence of artificial selection. The plow has come to symbolize the Neolithic Revolution, but viewing history in the light of evolution we see that it was intelligently designed changes to the genetic composition of natural biota that made the real tools. In some sense, Neolithic farmers were the first geneticists and domestic agriculture was the lever with which they moved the world.