Amid This Fog Of Ignorance

Nonhuman animal sounds jump the fence into the culture of our own species. When recordings of humpback whales inspired a generation of ecological activists, when musicians from Sibelius to Pink Floyd weave bird sound into their creations, when our onomatopoeic verbs croak, twitter, and bellow, or when police sirens evoke the howl of wolves, fragments of animal sound from other species lodge into human imagination and spread through our own webs of listening, remembering, and responding. Cultural evolution, in breaking free from the rules of genetic inheritance, regains this lost rapidity and fluidity of evolution, allowing behaviors to jump from one animal to another through the process of learning. There are limits, of course. Genes and anatomical constraints set bounds on what animals attend to and copy. Sparrows will not learn the calls of ravens, and whales do not mimic toadfish. Within these boundaries, cultural evolution samples, remixes, and connects, reclaiming a little of the evolutionary nimbleness of our bacterial ancestors. The brains of birds and mammals have each taken their own paths since this split, resulting in parallel worlds of sensation and experience. Birds cram a higher density of nerves into their skulls than mammals, giving their small brains as many cells as much larger primates. The folds and layers of the forebrain have different geometries, hierarchically layered in mammals and clustered into nodes in birds. But despite the long separation of our lineages, our vocal learning converged on some similar processes. Social learning has some universal qualities.

Ever Decreasing Circles

The first of these parallels is evident when we hear human infants and young birds babble. My parents tell me that half a century ago I could not manage the sophisticated tongue and lip movements needed for cat and chocolate, and so in my infant voice felines were vuff and treats were clockluck. But motor control is not the only aspect of maturation. The order, pacing, and form of sound in young birds and humans are more diverse than those of adults, coming in streams unconstrained by the rules that allow meaning to be conveyed. Vocal learning also gets harder as birds and humans age. Human adults struggle to grasp the rudiments of new languages, even though as infants we readily master any language we are immersed in. The winnowing and clipping that birds and mammals experience when learning to vocalize also shape forms of growth and maturation in other beings and at other time scales. Twigs on a tree ramify in tens of thousands of directions. Only a few mature into stout branches, and the rest are dropped, food for worms. Animal bodies develop partly through expansive early growth later trimmed by the programmed death of cells. In both birds and humans, vocal perception and memory are controlled by different parts of the brain than vocal production. Listening, memory, and action are each sequestered into their own spaces, and their activities are similar in humans and birds.

Good Times Bad Times

The perception centers of the brain are tuned by unknown means to the sounds most relevant to each species. These centers feed sonic information to the parts of the brain that control muscles and nerves. Underlying these feedback loops in the brain are the genes that build the brain. The same genes build parts of the nerve network needed for vocal learning in humans and songbirds, despite the very different forms of the mature brains of humans and songbirds. The patterns and processes of learning, too, are similar. To smile when we hear the tumbling, inchoate songs of birds is not mere sentimentality, then. The pleasure rising within us is a reminder of kinship across difference. Kinship, but also particularity. We’re a peculiar species. Among our close kin, the primates, there are no other species nearly as adept at vocal learning as we are. The complex behaviors and cultures of these other primates are based on visual and tactile observation, not vocal learning. These nonhuman primates also seem to have different brain functions.

What You're Doing

Those brain regions that are essential for vocal learning in humans play only a minor role in vocal production in other primate species. There is uniqueness here, one seized upon by those seeking to carve out a special place for humans in the natural order. But the cultural evolution of sound in birds, whales, and other vocal learners suggests that human vocal learning is not so much unique as parallel. There are multiple paths to vocal learning and culture within the animal kingdom. Like the evolution of wings in bats, birds, and insects, evolution has produced vocal learning through bodies of different design. In any convergent evolution of this kind, we expect each independent invention to have its own features. Ranking one as superior to the others seems absurd. Yet humans like to reserve language for ourselves. On what basis do we make this distinction? Humans are not unique in learning, intentionality, possession of vocal culture, evolution of culture over time, encoding meanings in sound, or representing in our speech external object or internal states. Every species has a logic, a grammar, to its sound making. It is not clear why only one of these grammars should qualify as language, nor is it obvious which dimension of grammatical refinement should be used as a yardstick. Birds, for example, are superior to humans at discriminating the subtle nuances within individual sounds, seeming more attuned to the rules and syntax contained in syllables than the arrangements among strings of syllables. If this capacity were the measure of language, we’d be ranked below sparrows. We have only a rudimentary knowledge of sound making and vocal learning in other species, a hazy and imperfect gaze into the complex vocal lives of others. Yet even amid this fog of ignorance, we clearly see our own species as just one of a multitude of speaking, cultured beings. Many animals also learn the practical physical and ecological skills needed to thrive. This knowledge usually passes from one generation to another through close observation, not through elaborate sounds. Young vertebrate animals often spend years studying their elders in order to learn how to find and process food, where to migrate, how to build shelter, what to do when a predator arrives, and how to navigate the cooperative and competitive social world. Without this knowledge, they are lost.