Mark Pagel weighs up a study claiming that the origins of human language are rooted in gesture.
The Truth about Language: What It Is and Where It Came From
By Michael C. Corballis
“Anyone can speak Troll. All you have to do is point and grunt.” Fred Weasley's assertion in J. K. Rowling's Harry Potter and the Goblet of Fire could describe the origins of human language. That is, if psychologist Michael Corballis is right in The Truth about Language. For years, Corballis has been one of the chief proponents of the idea that language has its origins in gestures. His latest book traces that argument from gesturing primates up through modern neuroscience.
Language is generally considered the jewel in the crown of human superiority over other animals. It seems to pop up almost out of nowhere in our evolutionary past, and no other animal's communication comes close to it. Through clicks, hoots, barks, chirrups and bleats, some animals can inform each other of how they are feeling. And some, through gestures, can signal anger, impatience, dominance or submission, desire and attachment. But none can use these displays to convey a simple sentence such as “I kicked the ball”.
Being unique and powerful, human language is a siren to Darwinians, teasing us to examine how it arose, and from what. Corballis assigns a central role to the brain's mirror neurons, which seem to echo action in observation (in monkeys, mirror neurons fire when they reach to grasp objects, and when they observe another animal doing the same). Corballis points out that there is an overlap between parts of the mirror-neuron system and two areas in the brain's left cerebral cortex that are associated in humans with the production and comprehension of language — Broca's and Wernicke's areas.
Mirror neurons have their detractors (see P. Smith Churchland Nature 511, 532–533; 2014), but for Corballis they raise the possibility that language “evolved within a system that, back in our monkey days, was specialised for grasping things”. In humans, mirror neurons also seem to be involved with other actions. One is pointing. Conveniently for Corballis, this is one of the earliest milestones of communication in children ('look at that', 'please get that for me'), emerging around the first year, and signifying the beginning of shared attention. It is also disrupted in social disorders, such as autism. And the fine control of facial muscles required for speaking seems to share cortical circuitry with regions that control gestures.
Still, what is wrong with the view that our language grew from our hominid ancestors' capacity for vocalization? This was Charles Darwin's favourite explanation, put forth in The Descent of Man (1871). He thought that the capacity for complex vocal learning had deep evolutionary roots, extending at least as far back as our common ancestor with birds. Corballis counters that primate vocalizations, unlike gestures, seem barely under voluntary control. He contends that they emerge like nervous tics, more closely connected to expression of emotion than to a deliberate exchange of information. Vervet monkeys (Chlorocebus pygerythrus) famously have three different alarm calls, corresponding to predatory eagles, leopards and snakes. But an alarm call does not involve the give and take of a language, gestural or otherwise.
One suspects that many — such as the primatologist and ethologist Frans de Waal, author of Chimpanzee Politics (Johns Hopkins Univ. Press, 1983) — will find Corballis' assessment of primate vocalizations harsh. But primatologists such as Jane Goodall and David Premack share his views. Whatever the truth, Corballis writes with an academic's attention to detail in witty, self-deprecating prose. The combination of style and argument make The Truth about Language the best work yet on the gestural theory of language.
But what does it mean to say that language — the exchange of information between senders and receivers — arose from gestures? Gesturing may indicate a theory of mind, the ability to understand what others might know or be thinking; and surely that is a requisite for language. Humans take this understanding for granted, but it has proved difficult to show conclusively in other animals. Some dogs respond to pointing, but they have been selected to do so (and don't point things out to other dogs). Chimpanzees can point, but do it rarely: not what would be expected in routine social communication. Chimpanzees and other primates can follow others' gazes, but gazing is not an intentional act of communication. Indeed, following another's gaze is potentially an act of theft.
There the putative gestural trail goes cold in the long line of fossil hominins along the 6-million- to 7-million-year evolutionary path separating us from our common ancestor with chimpanzees. And yet this gap is where everything happened. Humans use language to promote learning, cooperation and the exchange of goods and services — a leap from occasional pointing. Our brand of sociality distinguishes our species as much as language does, and it is hard to imagine our social systems working without language.
One might equally argue that human language arose to exploit the psychological capabilities that make our advanced sociality possible. Corballis' position then has to be that gesturing provides the most likely evolutionary route to those capabilities. But this is a topic on which he says comparatively little. What we do know is that without those capabilities, we might still be pointing and grunting like the Trolls.