From Wild Animals to Domestic Pets, an Evolutionary View of Domestication
CARLOS A. DRISCOLL,† DAVID W. MACDONALD, and STEPHEN J. O’BRIEN†
Artificial selection is the selection of advantageous natural variation for human ends and is the mechanism by which most domestic species evolved. Most domesticates have their origin in one of a few historic centers of domestication as farm animals. Two notable exceptions are cats and dogs. Wolf domestication was initiated late in the Mesolithic when humans were nomadic hunter-gatherers. 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.
The first domestic cats had limited utility and initiated their domestication among the earliest agricultural Neolithic settlements in the Near East. 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. 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.
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.
DOMESTICATION OF DOGS
The domestication of dogs and cats (today’s two most popular companion animals) was a bit different from the barnyard animals. And although Darwin began Variation with a discussion of the dog and the cat, the two could hardly be more different from each other (or from contemporary barnyard domesticates) in temperament, utility, and evolutionary origin. Farm animals were food items (“walking larders”) brought into the human sphere at the transition point from hunting-gathering to agriculture (Clutton-Brock, 1999).
Dogs, the earliest domesticate, proved useful as guards and as hunters for the hunting-gatherers, and perhaps offered necessary lessons for subsequent domestication of other species (Muller, 2005). By contrast, cat domesticates arose much later (≈10,000 b.p.), after humans built houses, farms, and settlements.
The preponderance of molecular evidence points to an origin of dogs from the wolf, Canis lupus(Vila et al., 1997; Leonard et al., 2002). The molecular findings are also supported by a large body of archaeological evidence that implicates the Near East as a likely locus of definitive domestication [although dog domestication may have begun in Central Europe as early as the Upper Late Paleolithic (Clutton-Brock, 1999; Muller, 2005)]. Wolf domestication is seen as the result of 2 interwoven processes originating >14,000 years ago during our hunter-gatherer nomadic period (Clutton-Brock, 1995).
First, a founder group of less-fearful wolves would have been pulled toward nomadic encampments to scavenge kills or perhaps salvage wounded escapees from the hunt. Thereafter, these wolves may have found utility as barking sentinels, warning of human and animal invaders approaching at night (Lindsay, 2000).
Gradually, natural selection and genetic drift resulting from human activities began to differentiate these wolves from the larger autonomous population. Once people had direct interaction with wolves, a subsequent, “cultural process” would have begun
DOMESTICATION OF CATS
The domestication of cats took a different trajectory. Wildcats are improbable candidates for domestication (see Table 5.3). Like all felids, wildcats are obligate carnivores, meaning they have a limited metabolic ability to digest anything except proteins (Bradshaw et al., 1996). Cats live a solitary existence and defend exclusive territories (making them more attached to places than to people). Furthermore, cats do not perform directed tasks and their actual utility is debatable, even as mousers (Elton, 1953).
[In this latter role, terrier dogs and the ferret (a domesticated polecat) are more suitable.] Accordingly, there is little reason to believe an early agricultural community would have actively sought out and selected the wildcat as a house pet. Rather, the best inference is that wildcats exploiting human environments were simply tolerated by people and, over time and space, they gradually diverged from their “wild” relatives (Wandeler et al., 2003; Driscoll et al., 2009).
Thus, whereas adaptation in barnyard animals and dogs to human dominion was largely driven by artificial selection, the original domestic cat was a product of natural selection.
A comprehensive genetic examination of the Felis silvestris species complex by our group revealed the relationships between domestic cats and their indigenous wild congeners (Driscoll et al., 2007).
We typed 36 short tandem repeat loci and sequenced 2.6 kb of the mitochondrial genes ND5 and ND6 in ≈1,000 cats from wild and domestic settings, including representatives of registered-breed and random-bred pet cats from both feral and household environments. Phylogenetic and clustering analyses identified 5 genetically
