The human race has often been compared to immature, angry children, destroying their habitat and acting out without intelligence or restraint. The irony is, this may literally be true, the human race may actually be a race of children:
If there once were so many other human species wandering the planet, why are we alone still standing? After all, couldn’t another version or two have survived and coexisted with us on a world as large as ours? Lions and tigers coexist; so do jaguars and cheetahs. Gorillas, orangutans, bonobos, and chimpanzees do as well (though barely). Two kinds of elephants and multiple versions of dolphins, sharks, bears, birds, and beetles—countless beetles—inhabit the planet. Yet only one kind of human? Why?Why Are We the Last Apes Standing? How childhood let modern humans conquer the planet. (Slate)
More than once, one variety may have done in another either by murdering its rivals outright or outcompeting them for limited resources. But the answer isn’t as simple or dramatic as a war of extermination with one species turning on the other in some prehistoric version of Planet of the Apes. The reason we are still here to ruminate on why we are still here is because, of all those other human species, only we evolved a long childhood.
Over the course of the past 1.5 million years, the forces of evolution inserted an extra six years between infancy and pre-adolescence—a childhood—into the life of our species. And that changed everything.
Why should adding a childhood help us escape extinction’s pitiless scythe? Looked at logically, it shouldn’t. All it would seem to do is lengthen the time between birth and mating, which would slow down the clamoring business of the species’ own continuance. But there was one game-changing side effect of a long childhood. Those six years of life between ages 1 and 7 are the time when we lay the groundwork for the people we grow up to become. Without childhood you and I would never have the opportunity to step away from the dictates of our genes and develop the talents, quirks, and foibles that make us all the devastatingly charming, adaptable, and distinctive individuals we are.
Childhood came into existence as the result of a peculiar evolutionary phenomenon known generally as neoteny. The term comes from two Greek words, neos meaning “new” (in the sense of “juvenile”) and teinein meaning to “extend,” and it means the retention of youthful traits. In the case of humans, it meant that our ancestors passed along to us a way to stretch youth farther into life.
More than a million years ago, our direct ancestors found themselves in a real evolutionary pickle. One the one hand, their brains were growing larger than those of their rain forest cousins, and on the other, they had taken to walking upright because they spent most of their time in Africa’s expanding savannas. Both features would seem to have substantially increased the likelihood of their survival, and they did, except for one problem: Standing upright favors the evolution of narrow hips and therefore narrows the birth canal. And that made bringing larger-headed infants to full term before birth increasingly difficult.
If we were born as physically mature as, say, an infant gorilla, our mothers would be forced to carry us for 20 months! But if they did carry us that long, our larger heads wouldn’t make it through the birth canal. We would be, literally, unbearable. The solution: Our forerunners, as their brains expanded, began to arrive in the world sooner, essentially as fetuses, far less developed than other newborn primates, and considerably more helpless.
One of the more intriguing byways in all this theory is the concept of regressive evolution, laid out in 1970 by psychiatrist David Jonas and anthropologist Doris Klein. Dr. Jonas had worked in neurology and tropical medicine before becoming a psychiatrist, and he was intensely interested in the animal roots of human behavior. Doris Klein had been trained in cultural and physical anthropology. In their book Man-Child, they said that nature only seems to progress in an unbroken triumph of successful, more complex forms. One reason this had often been overlooked was the traditional attitude toward the subject, which tended to deny backward or sideward evolutionary changes. Another was that most evolutionary failures, from disastrous mutations to species with one fatal flaw, weren't around long enough to leave a fossil record. Even among the successful, long-lasting forms of life, say Jonas and Klein, evolution was not always a straight march from fitter to fittest, and humans are the best possible example. This is not to say that human evolution was degenerative, but that it began with disaster, and proceeded by ingenious use of the wreckage. This crucial trait was neoteny, the persistence of childlike traits into adulthood.Napoleon's Glands, pp. 231-234. See also: Did STDs help human beings evolve? (Slate)
More than a half century ago, Dutch anatomist Ludwig Bolk pointed out striking resemblances between the adult human and the chimpanzee just before birth - hairlessness, roundheadedness, small teeth, flatness of face, absence of bony brow ridges, thin nails, and dozens of other details. These traits all fade in the chimp as it matures, but they remain in some degree in humans throughout life. "Physically," said Bolk, "man is thus a sexually mature primate fetus." Jonas and Klien say this isn't because apes descended from a more human looking ancestor, but because humans keep their primate fetal and infant qualities.
In behavior as well, humans resemble newborn apes more than they resemble adult apes. In chapter 8 we said how extreme human noeteny is, and how basic to human nature. It exists to some extent in many primates and sea mammals, such as chimps and dolphins, but in no creature nearly as much as man. At all ages, humans keep much of the playful, exploratory, inventive capacity that kittens, pups, and even young primates pretty much outgrow. These qualities allow humans, a species without powerful offensive or defensive equipment, their best chance to adapt and survive.
Neoteny, then, is an apparent backward step in body and behavior that enables our forebearers to learn, change, and dominate their environment. Jonas and Klein say that neoteny tends to come to the fore when a species faces a survival crisis, and every ounce of adaptive capacity must be called on. They speculate that the crisis which made humans so extraordinarily neotonous was the one they think brought our ancestors down from the trees and pushed them upright - a violent pandemic of some blood-borne viral disease that almost wiped them out.
Viruses are the subject of as much research and changing theory as evolution. One must specialize in the field and read heaps of journals each week to keep from making statements that are mistaken, or, at best, out of date. I think it is safe, though, to call a virus a large, complex molecule resembling the chains of protein and nucleic acid in a cell's chromosomes. A virus invades a cell, enters its nucleus, feeds, and reproduces; in the process, it may cause mutations or genetic recombinations in the host that can be passed on to future generations. This has led some scientists to speak of viruses as being, in effect, free-floating genes, Furthermore, viruses themselves can undergo mutations, making possible a vast variety of subtle genetic interactions with their hosts.
Viruses thrive especially in parts of the body that are richly supplied with blood, such as the midbrain. The viruses causing measles, rabies, herpes simplex, polio, and encephalitis can and often do inflame the brain. the short-term effects may be weakness, apathy and irritability. Long tern, there may be paralysis or brain damage; until recently, viral brain infections left many people disabled, severely crippled, or with emotional and intellectual deficits. Such common childhood viral diseases as rubella and encephalitis are probably still responsible for a great deal of mental retardation and emotional disturbance.
Given this information, imagine a viral pandemic, a cycle of recurring infections like polio or encephalitis, striking moneys or apes adapted to living in trees. If the disease was new to the species, the death rate and crippling would be enormous. The few survivors, their motor abilities savaged by disease, could no longer swing about in the trees. Weakened, they would have to descend to the ground and try desperately to survive there. Such epidemics may have occurred many times during primate history; only once, say Jonas and Klein, would a handful of handicapped survivors have had to succeed to start the trend of evolution toward human beings.
Perhaps at first only a few of these primates managed to get by precariously, barely managing to feed themselves, escape predators, and reproduce. Their descendants would make a marginal adaptation, future generations a more successful one, with rapid changes in behavior, anatomy and immunity patterns - helped perhaps by a few lucky virus-induced mutations. Trying to adapt to a new ecological niche, they would capitalize on the flexible ways of youth to compensate for their physical weakness, drawing on their inventive, exploratory behavior to the utmost. If the results helped them to survive, the neotonous traits would become part of the gene pool of the emerging new species. "It may be a distressing thought," say Jonas and Klein, "but these sickly primates were surely the forerunners of man."
Social scientist Lionel Tiger has objected that this sound like a primate version of Lord of the Flies, with virus-crippled primates staggering their way to becoming a new species, thanks to a wealth of lucky mutations and a regression to more infantile traits. There are no end of objections and alternate theories. However, Jonas and Klien back up their thesis with strong, detailed arguments about the nervous and hormonal system and about viral infections. They profess that they are playfully juggling a wide range of evidence and offer only a theory, a proposition to be proven true or not true. But it is especially interesting for its use of ideas too often lacking in evolutionary theories.