Getting There (evolutionarily speaking)

Share

Author: Jake Page

page.jpg

What on earth are we doing here? Us humans. I don’t necessarily mean stuff like using up too many resources, sending the global climate into a scary new orbit, or being nasty to one another. I mean how did we—who are pleased to call ourselves Homo sapiens, or wise man—arise and take such a dominant, even domineering place on this planet? Is there a Great Scheme of Things, and, if so, what is it in that scheme that we represent? A goal inherent in the universe perhaps? Some urge that existed before the Big Bang? Or are we, as E.M. Forster asked, “parting figures in a pointless universe?"

It would be nice if the sciences could tell us something about that—physics maybe. Physicists, after all, are the ones who seek to explain the fundamental nature of the universe. The dazzledance of particle physics is a busy place of electric charge, virtual spin, four-dimensional spacetime and incomprehensibly small measurements, such as one ten million billionths of a millimeter. Somehow, in that strange world, a few physicists found a reason for the existence of humanity. It was called the anthropic principle. It suggested that the exact dimensions and subatomic activities of the universe—and only those exact dimensions and activities—permitted the existence of humanity, thus providing the universe with a means of reflecting upon itself.

Having barely passed a physics-for-poets course back in the early Holocene, I’ve never had the sense that the universe really had me in mind for that job, or anyone else who is a bit befuddled by particle physics. Instead, this version of what might be called intelligent design appeared to celebrate exclusively the existence of only a particular priesthood—physicists themselves.

It is pretty hard to snuggle up to such an apparently lifeless and bizarre place as that inhabited by quarks, muons, gluons and even some particles that are so evanescent as to possess no mass. (And you thought the very definition of a particle is something that possesses mass, right? Sorry.) It may be just too big a leap from particle physics to humans.

I prefer to look back some 15 million or so years ago—a nice manageable number—when the world was full of rain forests, and the forests were full of many different kinds of apes, and the earth began to dry out. In response, some of the apes began to spend more time on the ground than in the trees, and as the millions of years passed some of them began to spend more time on two feet than on four. Walking on two feet, rather than knuckle-walking around on four, is much less energy-intensive. With the forests deteriorating, getting more sparse, open and dry, a creature that used less energy to reach a fruiting tree would have gained an advantage. It was this—bipedalism—that allowed humanity eventually to come about. The word “allowed” is important here. Nothing that scientists know about forced some bipedal apes to turn into humans: It took a long time and occurred as a result of a long series of largely unpredictable contingencies. Many people resent the claim that our existence here is a result of a whole lot of accidents, but that seems to be the way evolution works.

Those bipedal apes

In any event, by about 7 million years ago in what is now Chad, there lived a creature who seems to have been the ancestor of both the lineage of chimpanzees and the lineage of humans. Discovered in 2002 and called Sahelanthropus tchadensis, it had characteristics of both lineages and probably walked upright. By 3 million or 4 million years later, a young woman evidently drowned in a lake, to be discovered by Don Johanson in the late 20th century and named Lucy—a reference to the Beatles’ song that was being played in camp that day. Lucy was about 4 feet tall and remarkably intact. She was dubbed Australopithecus afarensis (meaning southern ape from Afar, a place in Ethiopia).

Australopithecines were pretty much bipedal apes, though they are universally considered distantly but directly ancestral to humanity—a road that is becoming visible these days but, as noted, only in retrospect. Lucy’s brain was about the size of a chimp’s and her toes were still a bit prehensile, suggesting that she and her kind still retired at night to the trees. She was judged a female because her pelvis was smaller than other presumably male Australopithecine pelvises, but that is really an educated guess. She could just as easily have been called Luke. But it is nice that Lucy’s pelvis seemed female because it draws our attention to the fact that the human female pelvis is one of the most important features of human evolution.

You see, human babies are typically born backward. Among apes and monkeys and other primates such as lemurs and tarsiers, the birth canal through the pelvis is large enough for a baby’s head to slip through quite easily. A chimpanzee birth takes about 20 minutes or less, and the mother needs only squat, reach down and help the little one out. The human female pelvis had to “improve” on this because humans are erect, bipedal. If the human female pelvis were big enough for a baby to slide out easily, then the legs of the mother would have to be so far apart that she could not stride forth across the land but would instead waddle awkwardly, placing her foot forward and then swinging her weight around it and forward, over and over. The human female pelvis is comparatively narrow from side to side so the woman can run if needed, and walk easily. Which means the birth canal has to be less straightforward.

To accommodate the relatively large and oval-shaped head of a human baby, the birth canal is barely bigger than the baby’s head, and it twists, forcing the baby to turn 180 degrees on its way to the outside world. It therefore comes out facing rearward, not forward like all the other primates. If the mother reached down to help pull the baby out, she might easily snap its neck. This sounds like a pretty unpromising evolutionary development, except for one thing.

As all of this tricky anatomical rearrangement evolved over the millennia many lonely tragedies no doubt took place, but those birthing mothers who were assisted by other females surely had greater success. Midwifery is, we can assume, the oldest “profession,” and became the norm. (Some cultures, such as the !Kung of the Kalahari desert, say their women give birth alone, but such rules are typically more honored in the breach, as it were.) In these intimate and vitally important events, women were socially engaged, and extreme sociality is one of the leading characteristics of humans. It is interesting to note that modern studies have shown that the mere presence of any woman during another woman’s labor and birthing significantly improves the chances of a healthy birth and a close tie between mother and infant. The presence of a male (any male) no such effect or sometimes the reverse.

The sociable women

While all this is going on, one feature of all mammals—a hormone called oxytocin that promotes both lactation and contractions—came to serve another purpose. It plays a major part in ameliorating the effects of stress among women. Both sexes respond to a sudden danger by the familiar fight-or-flight response—a blast of adrenaline. But in protracted stress conditions the female brain produces a large amount of oxytocin, which promotes what has been called a tend-and-befriend reaction. In this, women tend to gather together, round up the children and talk. Again, a highly sociable reaction to events.

In yet another feature of human birth, where the baby’s head typically has to squeeze through the convoluted birth canal, the bony plates of the baby’s skull are shoved away from the top of the head, leaving that famous soft spot. Talk about a contingency.

The baby’s head is pretty big at birth but will continue to grow at a rapid rate for the next few months. Some say a baby’s first three months outside the womb should be considered a fourth trimester. This continuing growth could not happen but for one of the tiny genetic differences between humans and all the other monkeys, apes and so forth—a difference in the 10 genes that control the formation of a muscle protein called myosin.

In 2003 a University of Pennsylvania scientist, Hansell Stedman, was studying the human genome for clues to the awful disease of muscular dystrophy. He found that one of the 10 myosin-promoting genes in humans lacked two base pairs of amino acids—making that gene different from all the other primates. Curious, Stedman probed further and found that this errant gene in humans had the effect of making the human bite muscles weaker. In apes and others, the bite muscles are strong and are attached from the jaw to a bony crest on the top of the head, creating a lot of what you might call jaw power. During the growth of a baby ape, once these muscles are attached to the crest, the skull cannot grow any larger.

Stedman reasoned that with the reduction of bite muscles in humans, which evidently took place some 2.5 million years ago, the youthful skull of early human-like creatures (called Homo habilis) could grow for a longer period and therefore accommodate a larger brain. The scientist called this change in the gene the RFT mutation—"room for thought.”

The human genome contains some 3.1 billion base pairs. Of those, humans have 40 million or so that are different from those of chimpanzees. So there are some 40 million ways that we are, by tiny increments like this one myosin gene, different from our closest relatives in the animal world. That’s a lot of contingencies, tiny changes here and there, that occurred over some 7 million years that have added up to so huge a difference. It’s a little like the spooky world of particle physics—where something seems to be tiny and huge at the same time. No one would ever confuse a chimp with a modern human—the differences are too vast and obvious—but those 40 million base pairs represent only about 2 percent of our overall collection of genes. We are genetically closer to chimps than coyotes are to wolves.

Think of it! Ninety-eight percent of our basic ground plan is there to create what we might call our animal nature. That being the case, we presumably overlook our animal nature at our own peril. After all, we share oxytocin and all our other hormones with the other mammals of the world. The remaining 2 percent (some say 2.5 percent, others say less than 2 percent, but, hey, this ain’t physics yet) is responsible for that part of our make-up that has created such things as the cathedral of Notre Dame de Paris, Hamlet, the laser, the Internet and, of course, weapons of mass destruction, not to mention sweet reason. And it can be fairly said that all of this human achievement is the result of the unique human invention of language—using meaningless arbitrary sounds to add up to meaningful communications, an open-ended system of symbols that can describe virtually anything in the world or in our dreams about the world.

Talking about language

How language arose is a question so full of opinion and so lacking in facts that an august French academy banned its discussion in the 19th century lest violence break out among the scholars. But the chances are good that it was female humans who put language on the road.

When a mother of an infant was out gathering nuts or berries, for example, she would occasionally have to put the infant down so that she could reach or climb up or whatever. Infants do not typically like to be relinquished in that manner, not feeling the warmth of the mother’s flesh and the rhythmic beat of her heart. Thus might have come into being what anthropologist Dean Falk of Florida State University calls “motherese,” sounds that would reassure the infant that the mother was still nearby. This might well have emerged as a kind of singing. And this form of communication might well have evolved into something like true language as a result of the growing complexity of human society.

By some 70,000 to 100,000 years ago, some humans were living longer lives. Families often consisted of three generations, with the experience of grandparents proving valuable, as well as their help in child-rearing. Managing a more complex social group calls for a great deal of attention to the varying emotions, needs, tasks, health and safety of all hands. Most students of language origins agree that it was a necessary tool for an increasingly complicated social world. There also is virtually universal understanding today that, on average, women are better at reading the emotions of others and better at verbal communication, while men typically outdo women in tasks calling for spatial cognition and skills.

As a result, as we all know, women tend to talk more and talk more about human relationships, while men typically refuse to ask for directions. But surely there is more to the human condition than that. The science of evolutionary biology does not, alas, specify or even hint at a purpose to the existence of life, including human life, on this planet. For such purposes, one must go elsewhere than science, which, of course, is only one of many ways of looking at the world. Even so, in evolutionary biology’s re-creation, however incomplete, of the long and improbable and wondrous saga of our coming into being, it does suggest that our approach to the world around us would be enhanced by an attitude if not of awe then at least of humility. After all, but for the grace of a few million mutations over a few million years, we might have turned out to be just another kind of chimpanzee.

Jake Page, a writer living in Colorado, is most recently a co-author with James Adovasio and Olga Soffer of The Invisible Sex, an archeological look at the roles of women in evolution and prehistory, just published by Smithsonian/Collins.

Photo of Jake Page is by Susanne Page.

The magazine welcomes comments, but we do ask that they be on topic and civil. Read our full comment policy.