If you want a no-fuss, no-muss pet, consider the Bengalese finch. Dubbed the society finch for its friendliness, breeders often use it to foster unrelated chicks. But put the piebald songbird next to its wild ancestor, the white-rumped munia, and you can both see and hear the differences: The aggressive munia tends to be darker and whistles a scratchy, off-kilter tune, whereas the pet finch warbles a melody so complex that even nonmusicians may wonder how this caged bird learned to sing.
All this makes the domesticated and wild birds a perfect natural experiment to help explore an upstart proposal about human evolution: that the building blocks of language are a byproduct of brain alterations that arose when natural selection favored cooperation among early humans. According to this hypothesis, skills such as learning complex calls, combining vocalizations, and simply knowing when another creature wants to communicate all came about as a consequence of pro-social traits like kindness. If so, domesticated animals, which are bred to be good-natured, might exhibit such communication skills too.
The idea is rooted in a much older one: that humans tamed themselves. This self-domestication hypothesis, which got its start with Charles Darwin, says that when early humans started to prefer cooperative friends and mates to aggressive ones, they essentially domesticated themselves. Along with tameness came evolutionary changes seen in other domesticated mammals—smoother brows, shorter faces, and more feminized features—thanks in part to lower levels of circulating androgens (such as testosterone) that tend to promote aggression.
Higher levels of neurohormones such as serotonin were also part of the domestication package. Such pro-social hormones help us infer others’ mental states, learn through joint attention, and even link objects and labels—all prerequisites for language, says developmental psychologist Michael Tomasello of Duke University in Durham, North Carolina, who studies social cognition.
In recent papers and at Evolang, a biannual conference on language evolution held here this spring, researchers turned to birds, foxes, and bonobos to help understand how domestication may have paved the way for language. Constantina Theofanopoulou, a neuroscientist at the University of Barcelona in Spain who convened the Evolang workshop, calls it the “most promising” working hypothesis to account for the thorny problem of language evolution, because it “puts together evidence from different levels of biological analysis: the anatomical, the brain, the endocrine system, and behavior.”
Read more: Science