Domesticated species: It takes one to know one

Abstract

Darwin was fascinated by both the process and outcome of our own species’ efforts toward the domestication of the plethora of others that became so central to our unparalleled success (1). In fact, he documented many of the various traits and behaviors that we have so purposefully selected. He was clearly enamored by the decreased aggression, increased gregariousness, reduced tooth size, shortened muzzles, smaller brain size, curly tails, floppy ears, increased reproductive success (fertility), and relaxation of the estrus cycle that seemed to accompany such docility. More recent investigations have revealed that domesticated species also possess modified adrenal gland function, novel neurotransmitter levels, and a prolonged juvenile learning period (reviewed in refs. 2 and 3). In PNAS, Kaminski et al. (4) report that an enhancement of the muscles of facial expression can now be added to this list, at least for the domesticated dog. They found that domesticated dogs possess musculature around the eyes that allows them to raise their inner eyebrows, creating an expression that, in humans, is associated with sadness (i.e., “puppy dog eyes”). Equally important is the absence of this trait in wolves, the ancestral species that served as their predomestication ancestor at least 15,000 y ago (5). The evolution of increased facial expressiveness surely has contributed to the canine success of securing their designation as our “best friend.” In terms of the process of domesticating species, it seems that we first honed our skills much closer to home, with ourselves (6). The idea that humans underwent a process of self-domestication has been entertained as a major evolutionary force since Darwin’s time. However, Darwin was careful to differentiate the human condition from that of domesticated plants and animals since humans were never subject to controlled breeding by another species (7). Nevertheless, humans and our domesticated animals have … [↵][1]1Email: mraghant{at}kent.edu. [1]: #xref-corresp-1-1