“Language seems to be a miracle; even our closest relatives, the great apes, lack any capacity for the grammatical structures that make human language unique. Herbert Terrace goes further and shows that chimpanzees can’t even learn words. With characteristic clarity, he gives a convincing account of language evolution in Darwinian terms, without appeal to miracles. This is an important new approach to an old and vexed problem.”
~ Micheal Corballis, author of The Truth About Language: What It Is and Where It Came From
Today, we are sharing the the next edition in this blog post series on The Origins of Language, by Herbert S. Terrace, author of Why Chimpanzees Can’t Learn Language and Only Humans Can. In this post, Terrace discusses the circumstantial evidence that Homo erectus invented words.
Originally published in PsychologyToday.com.
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Given that chimpanzees, our closest living ancestors, are unable to learn language, we have to ask if there is a now-extinct human ancestor who made the leap from animal communication to language. Some linguists and biologists have proposed Homo erectus, an early human species which evolved nearly 2 million years ago in Africa. Although empirical verification is not possible, there is circumstantial evidence that Homo erectus invented words.
Before considering that evidence, we should be clear about what evolved and why. Most linguists agree that the transition from animal communication to language occurred in two steps: first, the transition from animal communication to words (in “protolanguages”) and then, the transition from words to syntax. Only a few linguists, notably Noam Chomsky, have argued that words and syntax emerged simultaneously (Berwick & Chomsky, 2016).
“Protolanguages have words but no syntax. Like beads on a string, words can occur in any order.”
Protolanguages have words but no syntax. Like beads on a string, words can occur in any order. To state why words were invented we must consider two facts about Homo erectus: the size of its brain, which was approximately three times larger than a chimpanzee’s, and the demands of the environment in which it evolved.
The extra brain power of Homo erectus required a disproportionally large number of calories. Meat was an efficient source of those calories. Homo erectus’ environment included more open grasslands than the environments of earlier human species, a source of food that provided nourishment for many hooved animals. The populations of those animals increased around the same time that Homo erectus evolved. Although Homo erectus lacked the technology needed to hunt those animals (such as spears or bows and arrows), they could use stone tools such as hand axes and sharp flakes to cut through the hides of dead animals to obtain meat, marrow, and other nutrients.
“Homo erectus, which had a tall and slender physique similar to modern humans and walked (and probably ran) on two legs quite efficiently, could have covered a lot of territory looking for dead animals.”
Scavenging large animals was a group effort. First, a scout had to find a dead animal, for example, a zebra that was killed by a lion, or an animal that died of natural causes. That was the easy part. Homo erectus, which had a tall and slender physique similar to modern humans and walked (and probably ran) on two legs quite efficiently, could have covered a lot of territory looking for dead animals.
Having located one, the scout would return to his group to find others to help in scavenging the animal. That was the hard part. The scout couldn’t point to the dead animal because it was out of sight. Whether by gesture, sound, or some combination thereof, the scout had to inform his or her peers about the nature of the animal, its location, what tools to bring, and what was needed to ward off other predators or competitors.
“Derek Bickerton, a linguist, argued that to organize a group for scavenging, a scout had to use displacement—a feature of language that allows one to refer to objects that are not visibly present.”
What was needed was a type of communication that differed fundamentally from the innate and inflexible signals that animals use. Derek Bickerton, a linguist, argued that to organize a group for scavenging, a scout had to use displacement—a feature of language that allows one to refer to objects that are not visibly present. That could only be done with arbitrary words. Derek Bickerton, a linguist, argued that to organize a group for scavenging, a scout had to use displacement—a feature of language that allows one to refer to objects that are not visibly present. That could only be done with arbitrary words.
Evidence that supports Bickerton’s hypothesis about scavenging by Homo erectus comes from the locations of bite and cut marks on the bones of fossil animals. Defleshing bite marks are made by predators that ate meat from the animals. Cut marks are made by stone tools that hominins used to slice off the animal’s muscles and perhaps transport them to a safer place to process and eat them.
“Since Homo erectus did not have the technology to hunt large animals, the conclusion that they scavenged is inescapable.”
When cut marks lie above bite marks, it indicates hominin access to those bones only after other animals had defleshed them. When bite marks lie above cut marks, it indicates that hominins had first access to the bones, after which predators ate the scraps. In a study of 1.5 million-year-old fossil assemblages from Kenya, paleoanthropologist Briana Pobiner and colleagues found nearly 300 fossils with cut marks, but only a few with tooth marks. On the single fossil with intersecting bite and cut marks, the bite marks were on top of the tooth marks, indicating that hominins had first access to this carcass. Since Homo erectus did not have the technology to hunt large animals, the conclusion that they scavenged is inescapable.
For scavenging to work, Homo erectus needed an unprecedented degree of cooperation. Bickerton doesn’t comment on the source of such cooperation but, as mentioned in an earlier post, Sarah Hrdy (2009) argued that it was a consequence of the intersubjectivity instilled by cooperative breeding and that Homo erectus was the only hominin to engage in that practice.
“Trust in an alloparents’ benevolence was a consequence of their contribution to child-rearing. A mother would never engage in cooperative breeding and share care of her offspring unless she trusted members of her group.”
Compared to apes, whose mothers never allow others to care for their very young infants, infants in species that engage in cooperative breeding are cared for and provisioned not only by their mothers but by other members of their group (alloparents). For Homo erectus, trust in an alloparents’ benevolence was a consequence of their contribution to child-rearing. A mother would never engage in cooperative breeding and share care of her offspring unless she trusted members of her group.
Bickerton’s hypothesis that Home erectus invented words to communicate about scavenging is speculative, but it appears to be the only one that answers a question posed by Alfred Russel Wallace about how natural selection could account for language. Like Charles Darwin, Wallace recognized the extraordinary challenge that language posed for the theory of natural selection.
Wallace agreed with Darwin that language, like all other mental functions, was a product of natural selection. But about 10 years after the publication of On the Origin of Species, Wallace changed his mind. He asked how man’s “superior intelligence” could result from natural selection, a process that would expand a creature’s powers only to the point at which it has an advantage over the competition in the struggle for existence, that is, for its survival.
“Our early ancestors’ survival didn’t depend on their ability to do math, to compose music, or to speculate about the nature of the universe.”
Wallace wondered why humans have “a large and well-developed brain quite disproportionate to his actual requirement” (Wallace, 1870). The human brain is in fact much larger than is needed for its owner to survive and reproduce. Our early ancestors’ survival didn’t depend on their ability to do math, to compose music, or to speculate about the nature of the universe. Specifically, Wallace could see no problem solved by language that could not be solved without it; that is, no mechanism by which natural selection might have produced language.
There are many hypotheses about the evolution of language, e.g., toolmaking, pair bonding, grooming, and sexual selection, but none of them state why language was necessary for survival. Those activities could have occurred without language. Language would undoubtedly have enhanced them, but it wasn’t needed. Bickerton’s hypothesis that language was needed for communication about scavenging is arguably the only one that shows why language was needed for survival.