by Chip Walter
By continually refining these hand signals over the past twenty years, each succeeding generation of young children at Managua’s schools has improved their homespun language until now it no longer consists of crude, elementary gestures but a rich vocabulary capable of expressing every possible concept, from time and emotion to irony and humor. And what makes it truly amazing is the children managed this on their own without any central planning. No one sat down and wrote a grammar or created a dictionary. No one developed or taught a course. The language simply emerged naturally, out of the interaction of the children as they struggled to share what was on one another’s minds.
As humans they were so moved and driven to communicate that they invented a full-blooded language, which today is officially known as Nicaraguan Sign Language, and they did it from the ground up without even really meaning to. Yet, governed by a couple of key but simple and unstated rules—take small pieces of information and then assemble them in a hierarchical, orderly, and sequential way—they invented a form of communication as expressive as any in the world.31
The plight of these children is as close as we will ever come to witnessing a language evolve from scratch. And it may provide a glimpse into the past. Perhaps like these children our ancestors had an overwhelming need to communicate, but neither the voice nor the language to manage it. Yet over time perhaps they found a way. After all, it seems that the underlying rhythms, syntax, and building blocks for expressing thoughts and feelings run deeper in the human brain than the structures for sounding out words and syllables alone. The mind is driven to share information. It begs for expression any way it can manage the work, as the hand-babbling of babies raised by signing parents and the remarkable story of the mute children in Managua reveal, and hands seem to be the tool of choice. For those among us who are voiceless for any reason, they quickly become manual vocal cords.32 That could mean we were wired to communicate even before we could utter a single spoken word, and perhaps Homo erectus, or his descendants, mastered the form before he mastered speech, just as his forbears had learned to manipulate tools and weapons.
But powerful as gestures can be, and as much as they must have advanced and enriched the mental, emotional, and social worlds of our ancestors, they had their shortcomings. And before our predecessors could make their final leap to humanity, other adaptations awaited—among them one that was, so to speak, on the tips of their tongues.
III
Pharynx
Chapter 5
Making Thoughts Out of Thin Air
Elmer Gantry … was born to be a senator. He never said anything important and he always said it sonorously. He could make “Good morning” seem profound as Kant, welcoming as a brass band, and uplifting as a cathedral organ. It was a ’cello, his voice, and in the enchantment of it you did not hear his slang, his boasting, his smut, and the dreadful violence which (at this period) he performed on singulars and plurals.
—Sinclair Lewis, Elmer Gantry
For it is a very remarkable thing that there are no men, not even the insane, so dull and stupid that they cannot put words together in a manner to convey their thoughts. On the contrary, there is no other animal however perfect and fortunately situated it may be, that can do the same.
—René Descartes1
We already know that five million years ago the ancestral apes from which we sprung found themselves left to survive on Africa’s expanding grasslands. And we know that led to upright walking. But what we don’t know is precisely why Homo erectus strode into the picture almost perversely optimized for running. Finding the answer to that question, strangely enough, also illuminates how we became the talking animal.
For millions of years, evolution had been selecting for savanna apes of increasingly upright stature for several reasons, but the most compelling is probably that equatorial Africa was hot. A principle known as Bergman’s rule states that in colder climates an animal will tend to be stocky and spherical to reduce the amount of skin it exposes to the air. The less body area exposed, the rule goes, the less heat it will dissipate, and so it will stay warmer. The inhabitants of Siberia, for example, tend to have shorter arms and fingers, even in relation to their shorter, stockier bodies to reduce the amount of skin they expose to the cold air.2
The reverse is also true. A taller and more cylindrical body will cool rapidly because more of its skin is exposed. Any elongated body will lose more heat this way, but ours is especially good at this because it is (1) naked and (2) perforated with sweat glands, some two and a half million, depending on your exact size. Thanks to these tiny glands, which cover almost every centimeter of our body, we can efficiently scatter 95 percent of the excess heat we generate.
This is an unusual approach to cooling in the animal world. Most mammals don’t sweat much, they pant (possibly because they are mostly covered in fur, which restricts efficient sweating). And though other primates do have sweat glands—chimps, for example—humans have roughly twice as many.
Anthropologists generally agree that we sweat as profusely and efficiently as we do because if we didn’t we would now be extinct. And the reason we would be extinct is that we evolved from scavengers to hunters. By the time H. erectus emerged we were well on our way to becoming the most cunning predators on Earth. We didn’t have much in the way of claws and fangs, strength and speed, but we had the weapons we had created. And we could run.
No other creature is a better long-distance runner than a human being. Cheetahs may accelerate faster, ostriches and horses may gallop longer at high speeds, but no animal can cover more ground, without rest, than we can. The popularity of distance, marathon, and ultra-marathon running is a legacy of that ability, but there are plenty of other exotic examples of our peculiar bipedal talents. The Tarahumara Indians of northern Mexico, for example, routinely hunt deer by literally running them down over a period of days. They rarely get a close look at their quarry, but manage to stay near enough that the animal never has a chance to rest. Eventually the deer collapses from exhaustion, sometimes with its hoofs worn to nothing. The hunters, on the other hand, though tired, are far from dead.
The Nganasan people of Siberia use a similar method to hunt reindeer. They may follow an animal for six miles or more, hiding behind trees and piles of rock until they get within striking distance. Then with a burst of speed they close in and kill the deer. The Aché of Paraguay, the Agta of the Philippines, and !Kung San of the Kalahari Desert also use their legs and lungs to wear out their prey.3
This isn’t the only way to bring down supper, but H. erectus, so perfectly engineered for running as he was, almost certainly used the technique as one of several weapons in his arsenal. However, in a world of intricately evolving feedback loops, this would have created yet another problem. The solution to that problem may help explain why the brains of our ancestors expanded so suddenly between a million and two million years ago, laying the foundations for a mind capable of speech.
…
Brains are greedy and costly organs. Compared with the rest of the body, they gobble up energy and burn hot. The modern human brain consumes as much as 25 percent of an adult’s daily energy needs (more than twice that of chimps or gorillas). Ounce for ounce it devours sixteen times the calories that muscle tissue does.
Homo erectus’s brain was not as large as ours, but it was getting there, and by some estimates was burning up to 17 percent of its body’s energy budget.4 On the hot savanna an animal, especially one with a brain that large, running long distances would have grown very warm—so warm that it almost certainly would have collapsed from heat stroke, no matter how tall and no matter the number of sweat glands it had, unless it found other ways to stay cool.
Many of our ancestors probably did die eking out a living under Africa’s blistering sun, but some, our direct ancestors in particular, obviously didn’t. Why? Because according to one fascinating theory they developed a genetic mutation (or perhaps several) that provided them with an ingenious air-conditioning
system, one we still enjoy today.
Dean Falk, an anthropologist at Florida State University, believes that when our precursors first began scavenging for meat about two million years ago, they also began to evolve a network of cranial veins that cooled the blood running through their brains, faces, and skulls. She calls this the “radiator hypothesis” because the network operates something like a car radiator.
When we begin to overheat, the heart pumps cooler blood from the body and face into a fine network of “emissary” veins scattered in tiny branches throughout the skull near the scalp. Here, more heat escapes before the veins return air-cooled blood back to the brain, where it replaces the warmer blood that is already there.5,6,7 In other words, it’s a perfect natural radiator.
Falk developed this theory after closely comparing the skulls of modern apes, humans, and our ancestors. Though the veins and arteries that were once a part of these skulls were long gone, the skulls still revealed some of the vascular passageways that these creatures used. She found that we and apes have very different ways of moving blood to the brain, especially when it begins to overheat. Apes do not have nearly the complex system of heat-radiating emissary veins we do, and they have less effective ways, generally, of pumping cooler blood into the brain.
This also seemed to be true of early australopithecines such as Lucy, and evolutionary dead-end species such as Australopithecus robustus, both of which had more in common with jungle apes than with us. But the skulls of more recent species such as Homo habilis, Homo erectus, Neanderthals, and early Homo sapiens suggested that the emissary vein system progressively increased in size and complexity as the brains grew larger and as cooling requirements became more demanding.
In our species, Falk found the system rich and efficient, capable of radiating the majority of our body heat when we have worked up a sweat. (When you see the steam billowing off of a football player’s head on a frigid Sunday afternoon after he has taken his helmet off, you are witnessing this system at work.)
Falk’s view is that this cranial air conditioner coevolved with all of the other cooling mechanisms we were developing: the loss of our fur, our increasingly upright posture, our proliferating sweat glands. But it was especially crucial because without this adaptation the size of our brains would have been stunted, unable to increase much beyond Homo habilis size for the simple reason that any hominid on the savanna that didn’t enjoy its benefits would have died of heat stroke long before it had an opportunity to pass its genes along.
And perhaps this is why some lines of savanna apes did die out: they never developed a truly effective cooling system that enabled them to take up scavenging and, eventually, hunting under the savanna’s broiling sun. Hyperthermia can be a very efficient killer. A rise in the temperature of the human body of only four or five degrees Celsius above normal can scramble brain functions in humans that cause delirium, hallucinations, and convulsions. Vascular physiologist Mary Ann Baker has even written that the temperature of the brain may be “the single most important factor limiting the survival of man and other animals in hot environments.”8
So while the same old evolutionary pressures would have been dogging our ancestors, favoring greater tool use, better communication, and all of the increasingly complex behaviors that define our species, without the evolution of some sort of brain cooling system, these advances may well have found themselves cerebrally stuck in neutral, doomed at best to have left our ancestors as unchanged as their chimp and gorilla cousins.
On the other hand, if the system did evolve and work, as it seems to work in us today, then the lid, so to speak, would have been off. Now the brains of our ancestors would have been free once again to expand. With their evolving ventilation system, H. erectus would have been able to hunt the herds he followed, and develop the intellect needed to face the increasingly complex social interactions of the troop, until eventually his hominid brain evolved into the unusually large size we see in us today. (The human brain is about three times the size scientists would expect to see in a nonhuman primate of equivalent body size.9)
This made our ancestors’ blood-cooled brains, in Falk’s words, “a prime releaser,” if not a prime evolutionary mover. By that she means that this adaptation doesn’t stand with thumbs and toolmaking as a sea change in human evolution, but it enabled our ancestors to supply their reevolving brain the ability to grow still larger.
Exactly how would this new capacity be applied? If H. erectus was capable of some sort of gestured communication, but not yet capable of true speech, maybe it enabled certain parts of the brain already largely devoted to manual dexterity to grow and commandeer the hundreds of muscles and organs originally evolved for breathing and eating so that they could also meet the pressing need for increasingly refined and subtle communication. It may have enabled the brain to fully build out the raw neuronal power needed to transform our ancestors from the very bright, but largely mute, apes they were into the smooth-talking species we are today.10
But even as that happened, certain other reorganizations also had to take place in the elongating throats of the tall and lanky creatures that were now rapidly spreading across the planet. A new, strangely shaped chamber in their necks needed to develop, an organ called the pharynx. Because without it, speech would be impossible.
…
The pharynx is cone-shaped and about four-and-a-half-inches long. It sits right behind the root of our tongues and connects our mouth to our esophagus. Strangely enough, the human pharynx evolved, at least partly, because we took to running upright. When our ancestor hominids stood on their hind legs, their necks slowly began to straighten and elongate. Over time their shoulders and torsos centered under their heads, their brows grew less sloped, their jaws more square, and their skulls more rounded. All of these changes caused the roofs of their mouths to rise; their necks to stretch; and, most important of all, their tongues and larynx, or voice box, to drop farther down their throats.
Others animals have a pharynx, but the architecture of ours and the organs positioned within and around it make it unique; a specialization as odd as the necks of giraffes or the strange binocular eyes of hammerhead sharks. Despite some of the work done with the likes of Koko the gorilla or Kanzi the bonobo chimpanzee, no other primate has been blessed with a pharynx capable of the noisemaking legerdemain ours possesses.11
The descent of our larynx created a ticklish problem for our ancestors. The throats of other primates are arranged so that their nasal passages are connected directly to their lungs by a single airway, while another, separate route links their mouths directly to the stomach. These run like two parallel, nonintersecting roads from the skull, down the neck, and into the torso, and never share a centimeter of common real estate.
This was probably the case with all of our ancestors as well, until, perhaps, H. erectus. With H. erectus, whose upright alignment was virtually identical to ours, the shape and length of our skulls and necks likely forced our nasal passages and mouths to forsake their formerly separate routes and join one another, creating an intersection in the back of our throats. And therein lies the problem, because the formation of that intersection meant that the food and water coming from our mouths could cross paths with the air we were breathing. And choking was born.
These two diagrams show the throats of apes and australopithecines (left) and modern Homo sapiens (right). Unlike other primates the airway and esophagus of humans intersect. As a result we can choke, but we can also speak. (Reprinted from The Symbolic Species by Terrence Deacon, used by permission of W. W. Norton.)
Increasing the chances of choking wouldn’t seem to be an optimal evolutionary event. Even Darwin was surprised at this mutation. In fact, he seemed almost annoyed when he wrote in Origin of Species: “the strangest fact [is] that every particle of food and drink which we swallow has to pass over the orifice of the trachea, with some risk of falling into the lungs.”
To handle that danger, we have a small flap of skin and cartila
ge called an epiglottis, which folds over the top of our trachea to prevent food and liquid from free-falling into our lungs when we swallow. This small organ does occasionally fails us, however. Until the invention of the Heimlich maneuver, six thousand people a year died from choking in the United States, usually while talking and eating at the same time. This made it the sixth-leading cause of accidental death. A chimpanzee, however, will never choke to death, at least not because the banana it was eating went down the wrong pipe.
Making Words
An exquisite series of events unfolds every time our lungs pass air up through our throats where we bend, bite, and twirl our breath to rattle off a word as simple as “bread” or as convoluted as “supercalifragilisticexpialidocious.” Commanding all of the apparatus needed to speak with the easy, unconscious fluency each of us manages is a remarkable feat. The body and brain recruit over one hundred muscles to do the job, more than any other human, mechanical activity. When we speak we transmit twenty to thirty phonetic segments or six to nine syllables per second. This takes tremendously refined breath control, specialized muscles that can expand and contract with unparalleled rapidity, and fibers in the tongue that enable us to move and reshape the air we exhale with lightning speed.12
Not that scientists have a complete grasp of how these elusive processes work. They know that the human cerebral cortex—the largest part of our brain—has more direct control over the face, tongue, larynx, and lungs than any other mammal or primate, and a lot of that neuronal firepower is used when we speak, but they don’t understand the processes in all their detail.
In most mammals, facial expression, breathing, and the muscles of the mouth and throat are controlled by clusters of neurons called the reticular premotor area, an ancient part of the brain stem that is directly connected to our spinal column. In all animals the reticular premotor area controls many of the body’s unconscious, visceral activities, such as swallowing, blinking, or breathing.