Last Ape Standing: The Seven-Million-Year Story of How and Why We Survived (8 page)

It is possible that it didn’t, at least not all the time. Multiple species arguably walked down this Darwinian road and were snuffed out. Several—about whom we may never know a thing—were surely done in over time by the unrelenting pressures of protecting their helpless infants, braving their environment to get them more food, or becoming dinner themselves for some salivating savanna cat. Is this what wiped out
Australopithecus garhi
? Does this explain the demise of
Homo habilis
or
rudolfensis
? So far the sparse, silent, and petrified clues that the fossil record has left us aren’t parting with those secrets. They are stingy that way.

We do know this: around a million years ago or so—early November in the Human Evolutionary Calendar—the robust primates had met their end, and so had many gracile species, but a handful continued and even flourished. Already some had departed Africa and had begun fanning out east to Asia and the far Pacific. The cerebral Rubicon had been crossed and there was no going back.

This meant that evolution’s forces had opted, in the case of our direct ancestors, for bigger and better brains rather than more sex and more offspring as a survival strategy. And, against all odds, it was working—a profound evolutionary shift. Over time, in the crucible of the hot African savanna, far away in time from the Eden of rain forests, an exchange was made—reproductive agility for mental agility. If bringing a child into the world “younger” was what it took, fine. If expending more time and energy on being a parent was necessary to ensure that a creature with a bigger, sharper brain would survive, then so be it. If evolving an entirely new phase of life that created the planet’s first children was required, then it had to happen. The imponderable forces of evolution had made a bet that delivered not greater speed or ferocity, not greater endurance or strength, but greater intelligence, or put in flat Darwinian terms, greater adaptability. Because that is what larger, more complex brains deliver—a cerebral suppleness that makes it possible to adjust to circumstances on the fly, a reliance not so much on genes as on cleverness.

It is strange to think that events could well have gone another way. Earth might today be a planet of seven continents and seven seas and not a single city. A place where bison and elephants and tigers roam unheeded and unharmed, and troops of bright, robust primates live throughout Africa, maybe even as far away as Europe and Asia, with not a single car or skyscraper or spaceship to be found. Not even fire or clothing. Who can say? But as it happened, childhood evolved, and despite some very long odds, our species found its way into existence.

It is easier to build strong children than to repair broken men
.

—Frederick Douglass

Boy, n.: a noise with dirt on it
.

—Anonymous

Give me the child until he is seven, and I will give you the man
.

—Jesuit aphorism

Youth, the french writer François Duc de la Rochefoucauld once observed, “is a perpetual intoxication; it is a fever of the mind.” Ralph Waldo Emerson was more blunt: “A child is a curly, dimpled lunatic.” We have all witnessed a toddler or two in action (usually and most memorably our own), and it is a sight to see. The average two–year–old is thirty inches tall and twenty-eight pounds of pure, cerebral appetite determined without plan or guile to snatch up absolutely everything knowable from the world. She, or he, is, indisputably, the most ravenous, and most successful, learning machine yet devised in the universe.

It may not seem so on the surface, but toddlers accomplish prodigious amounts of work (all cleverly disguised as play) as they bowl and bawl their way through each day. By throwing a ball (or food), playing in the mud, a pool, or a sandbox, by attempting headlong runs and taking sudden tumbles, or swinging on swings or off “monkey” bars, the young are fervently familiarizing themselves with Newton’s laws of motion, Galileo’s insights into gravity, and Archimedes’ buoyancy
principle, all without the burden of a single formula or mathematical term.

When a toddler smiles, cries, grimaces, gurgles, giggles, spits, bites, or hits; when she breaks free of mom or dad for a wild dash down the sidewalk; throws whatever he can grab for the sheer joy of it; dances spontaneous jigs or engages in other diabolical antics—she is learning what is socially acceptable and what is not, what is scary, what works in the way of communication and what fails and when. Food, and much that isn’t food, is tasted, licked, and baptized with slobber to investigate its texture, shape, and taste. Yet no artifice or logic is behind the tasting. It’s just another form of exploration. Objects, living or not, are bounced, swatted, hugged, flailed, closely inspected, all in a fervent effort to comprehend their nature. Unbounded and unstoppable greed for knowledge is the best way to put it.

Acquiring language is another big job in childhood. Babbling, squeals, and other noises are, as the best linguists have so far been able to ascertain, ways of figuring out the language that the other bigger, parental creatures speak around the toddlers whether it is Swahili, German, or Hindi. Later, early conversations are short, generally. “Here! Mama! Dadda! Mine! No! Please. Want!” Often, in times of acute frustration, communication is inarticulate, loud, and punctuated with acrobatic body language. In time, however, and amazingly, vocabularies grow, syntax improves, and full sentences are expressed, all with hardly an ounce of formal instruction. The acquisition of language is one of the great miracles in nature. At age one few children can say even a single word. At eighteen months they begin to learn one new word roughly every two hours they are awake. By age four they can hold remarkably insightful conversations, and by adolescence they have gathered tens of thousands of words into their vocabulary at a rate of ten to fifteen a day and often use them with lethal effect! And nearly every word was acquired simply by their listening to, and talking with, the people around them.
¹

Children do these apparently lunatic and astonishing things for a reason. Nature has wired their brains for survival by driving them to swallow the world up as fast as they possibly can. Pulling off this feat is easier said than done. However, if we hope to comprehend how cerebral connections this complex take place, it might first be useful to step back and consider why brains exist at all, and how we eventually came by the particular brand we have.

* * *

By general agreement the first brain in nature belonged to a creature scientists today call planaria, known more commonly to you and me as the lowly flatworm. Flatworms are metazoans and wouldn’t seem therefore to be very brainy. But intelligence is a relative thing and planaria, when they first emerged more than seven hundred million years ago, were the geniuses of their time, creatures of unparalleled intelligence blessed with an entirely new kind of sensory cell capable of extracting marvelously valuable bits of information from their environment.

Unlike many of their contemporaries planaria were unusually sensitive to light, possessed rudimentary sets of eyes, and responded to, rather than ignored, changes in temperature—all radical innovations in their time. Even today they remain expert at sensing food, and then making their way with uncanny determination to it, while other metazoans (corals, for example) generally take a more leisurely approach to their cuisine, waiting for it to find them rather than the other way around.

Planaria—the Einstein of the Day

Among the cellular innovations that made an ancient flatworm’s brain possible was a protoneuron called a ganglion cell. These are clustered in the head of the worm and then connected to twin nerve cords that run in parallel down the length of its body so that certain experiences sensed alongside it can be transmitted to the flatworm’s brain for some metazoan cogitation. All the brains that evolution has so far contrived rest on this tiny foundation. So for the best ideas you
had today you can thank the determined metazoan that looks something like a squished noodle.
²

The purpose of brains generally is to organize the waves of sensory phenomena that nature’s cerebrally gifted creatures experience. Their job is to filter the world’s chaos effectively enough to avoid, for as long as possible, the disagreeable experience of death. A direct correlation exists between survival and how well a brain maps the world around it. The more accurately it can correlate, the more likely it will survive danger, discover rewards, and keep its owner among the living.

At the heart of every brain are its neurons, the specialized cells that make possible our brand of thinking, feeling, seeing, moving, and nearly everything else important to us. There are over 150 different kinds of neurons, making them the most diverse cell type in the human body. To support their greedy habit of consuming large quantities of energy, they are surrounded by clusters of glial cells, which serve as doting nannies busily shuttling nutrients and oxygen to them while fetching away debris and generally working to keep the neurons fresh and firing. Each of us carries roughly a hundred billion neurons clustered jellylike inside our skulls (coincidentally about the same number as stars cosmologists believe populate the Milky Way galaxy). Every one of them is supported by ten to fifty indulgent glial cells.

This makes our brains a remarkable and mysterious place still well beyond the comprehension of the thing itself (a fascinating irony), but the cerebral cortex of a growing human child is more remarkable still. Only four weeks after a human sperm and egg successfully find one another, when we are still embryos no larger than a quarter, clusters of neurons that will eventually become our brain are replicating at the rate of 250,000 every minute, furious by any standard. Around this time, a bumpy neural tube that looks suspiciously similar to a glowworm has begun to take shape. Over the next several weeks four buds within the tube will begin developing into key areas of the brain: the olfactory forebrain and limbic system—the seat of many of our primal emotions; the visual and auditory midbrain, which governs sight, hearing and speech; the brain stem, which controls autonomic bodily functions such as breathing and heartbeat; and the spinal cord, the trunk line for brain–body communication. Two weeks later a fifth cluster of neurons begins to blossom into the frontal, parietal, occipital, and temporal lobes of the cerebral cortex, where so many exclusively human brain functions reside.
³

The brain constructs itself this way, with neurons ebulliently proliferating, and then, like the rest of the cells in the embryonic body, they march off to undertake their genetically preordained duties. During this process and throughout our lives, every cell in the body communicates. It is in all cells’ DNA, not to mention our best interests, to reach out and touch one another, mostly by exchanging proteins and hormones. But neurons are especially talented communicators. This is because whenever the biological dice fell in such a way that they came into existence, they began to evolve specialized connectors—dendrites and axons—that vastly improved their exchange of information compared to other cells in the body.

Before brains came along, primitive protoneurons communicated by secreting hormones and electrical currents in no particular direction, mumbling their messages to the other cells and protoneurons in their vicinity, and not getting terribly quick results, at least compared with our current models. With the invention of dendrites and axons, however, they could form elegant, smart clusters that shared at high speed the information each of them held with the others nearby. (Planaria were among the first to accomplish this.)

The emergence of high–speed, if exceedingly minute, communications cables meant that any creature fortunate enough to inherit them could more fully and rapidly sense the world it inhabited—light and dark, food, danger, pain and pleasure—then react to it all in a blink. Not only that, the cables could link different sectors of the brain the way highways connect cities. This meant the brain could not only improve contact with the world, but also stay in better touch with itself, not a trivial matter as brains grew larger. (This turns out to be important to consciousness, but we will visit that subject later.)

Dendrites generally conduct signals coming into a brain cell while axons do the opposite. Dendrites (also known as dendrons) are so eager to make contact that they extend treelike in multiple directions and can place one neuron in touch with thousands of its neighbors. Axons aren’t nearly as obliging as dendrites, but can still make uncounted connections as they transmit signals outward when a neuron is stimulated and reaches what is known as a threshold point, a moment that is vitally important when it comes to thinking, feeling, and sensing. At that instant an electrical impulse bolts down the axon at 270 miles an hour. When it reaches the end of the axon, a tiny pouch of chemicals bursts, sending neurotransmitters across a synaptic gap
like party confetti, where they embrace the receptor sites of the next neuron like a long–lost relative and then pass along their message.