Language is one of the defining features of humans. While other species communicate with simple, nonverbal cues, and some may even convey relatively simple ideas using vocalizations (birds and whales, for example), we are the only species that has ever evolved the ability to communicate complex ideas using long strings of words.

Verbal communication is one of the most difficult things we do. Think about a typical conversation, which not only requires mastery of the grammatical rules that underlie the structure of the language, knowledge of a wide variety of vocabulary terms as well as short-and long-term memories to provide context, but also a complex set of motor skills involving roughly a hundred muscles in the face, mouth, and throat. The latter is important, as young children typically understand far more words than they can pronounce correctly. The real excitement of our language ability, though, lies within our brains.

Figure 1. Stone artifacts over the past one million years (top) show relatively little change until around 50,000 years ago, when complex technologies and the first evidence for art become widespread (bottom).

Chimpanzees, which lack the finely tuned motor apparatus necessary to produce speech, can be taught sign language as a means of communication. While they can construct a wide variety of two-word sentences to express simple ideas, like "eat banana" or "go outside," they lack the syntax necessary to produce a complex sentence such as the one you are reading now. Because of this great gap between us and other species, even intelligent ones like chimps, anthropologists believe that language developed relatively late in hominid evolution.

According to genetic data, the lineages leading to chimpanzees and humans split around six million years ago. These dates were arrived at through the same mechanism we learned about in Chapter Two, namely counting the number of nucleotide differences between human and chimp genes and making use of the known mutation rate to calculate how long they have been diverging from each other. Assuming that our first ancestor on the line leading to humans had language abilities no better than all other apes do today— almost certainly a valid assumption—this means that our language abilities must have developed in the past six million years. But when along the evolutionary path did that occur?

One way of answering this question is to examine the changing patterns of anatomy on the line leading to modern humans. While we are uncertain of exactly what our earliest ancestors looked like, they were more ape-like than we are. The first marked transition was the emergence of bipedalism, or walking upright on two legs. This happened long before the second major step forward—an enlarged brain—and could have arisen as early as 4.5 million years ago in the hominid Ardipithecus. Why hominids became bipedal is greatly debated, although rapid movement in the grassland environment where our early ancestors evolved was probably a contributing factor, as was reduced sun exposure during the heat of the day. Since brain size had not increased significantly, and tools are not in evidence from these early hominid sites, Darwin's theory that bipedalism freed the hands for tool use is an unlikely reason for them to walk upright.

The next major leap occurred when brains became bigger. Brain size leapt from an ape-like few hundred cubic centimeters in the australopithecines to 600 to 700 cubic centimeters in Homo habilis, the first member of our genus, and 800 to 1,200 cubic centimeters for Homo erectus. Hominids began to use tools during the time of Homo habilis, around 2.3 million years ago (Figure 1), and the increasing complexity of thought that this represented likely drove the increase in brain size.

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Brain size continued to grow for the next 1.5 million years, until by 500,000 years ago it measured 1,300 cubic centimeters, comparable to that of modern humans (see timeline above, Figure 2). These big-brained hominids would have been the ancestors of Neandertals as well, and we now know that the Neandertals had on average 10 percent larger brains than modern humans. Size isn't everything, though, as the results indicate: We drove the Neandertals to extinction within a few thousand years of entering their stronghold in western Europe, even though our brains were not as massive.

So why did we win out against the Neandertals? We were smarter, and our improved brains probably grew in tandem with the development of fully modern, syntactic language, like that we use today, which brings us to the final stage in the development of modern humans. While earlier hominids probably had the physical capacity to speak and may have done so as well—although in less mellifluous ways than a Shakespearean sonnet—they almost certainly lacked the brain wiring to be able to say much that was worthwhile. Their speech was probably limited to simple chimp-like statements along the lines of "go there" or "eat now." The speech-enabling hyoid bones (the bone in your Adam's apple) found in Neandertal remains attest to a throat structure that would allow spoken language, but the other cultural attributes (such as the fact that the Neandertals' basic tools had not changed in a million years) suggest that our brawny cousins had little to say.

Figure 2. Major advances in the development of modern humans over the past five million years

Human speech is part of a larger suite of characteristics that probably appeared about 50,000 years ago, according to anthropologists. The "Great Leap Forward," as biogeographer Jared Diamond calls the Upper Paleolithic transition in his book The Third Chimpanzee, represented a leap of understanding as opposed to anatomy. The difficulties faced during the last ice age probably led our ancestors of 50,000 years ago to develop better ways of exploiting the shrinking food resources in a harsh tropical environment. Genetic data suggest that the human population size crashed to as few as 2,000 people around this time, and archaeological data is quite sparse as well. But coming back from the brink seemed to have involved a cultural transition unparalleled in our species' long history of upward mobility.

Modeling the past and future involves creating a narrative, much like speech. Our way of understanding the world seems to involve telling a story about it: John walked from the beach to the house. This simple sentence tells us all we need to know, about the locations, the sequence (beach first, then house), and the mode of action (walking). It even suggests that John is still in the house, which gives us a good clue if we want to find John now, all contained in one simple sentence. Try to convey all of this using two word sentences and you soon get bogged down in a confusing variety of alternatives. John beach. John house. John walk. Beach house. What does it all mean? So syntax, and the inherent narrative structure it provides, is a great adaptation if you want to explain complex events (imagine describing how to program a number into your cell phone using two-word sentences).

This new ability to explain complex events—which probably included where to find succulent roots or fruit, or how to hunt rare prey on the dry grasslands 50,000 years ago—would have provided an enormous advantage to our ancestors. So great was this advance that every human alive today, barring a severe medical disorder, has the ability to speak. The diversity of languages is astounding, with more than 6,000 spoken around the world today. All rely on syntax to convey complex thoughts, and the language you are currently reading is a direct descendant of those first tentative syntactic steps that took place 50,000 years ago. These early steps probably allowed the shrinking human population not only to survive their dire predicament, but also to thrive, expanding their range from Africa to encompass all six habitable continents.

This expansion appears to have occurred quite soon after the great leap in brain function. After the wave populating southern Asia and Australia, a slightly later one, exiting Africa via the Middle East, led to the populating of much of the Northern Hemisphere. And some people stayed on in Africa, including Julius's ancestors. The uniting factor among all of these seemingly disparate branches of humanity is complex, fully modern human behavior. We are all the descendants of a remarkable set of ancestors who set in motion the way we look, act, and think today. The next stop on our journey will be to use genetics to tell more about who these people were and where they might have lived in


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