|A book by|
William H. Calvin
UNIVERSITY OF WASHINGTON
SEATTLE, WASHINGTON 98195-1800 USA
The Throwing Madonna|
Essays on the Brain
Copyright 1983, 1991 by William H. Calvin.
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Scanned, OCR'ed, and webbed -- but NOT proofread (14 Jan 97)
The how of human being -- every village gossip has been doing that since talking started.... It's the why of human beings you've got to understand.... Or else you'll be giving all your science to a mob of children. Whatever they do with it, they won't know why. We can never trust them. Unless they know the why about themselves, then everything in the world is like giving a child some poison and telling it to go and play in the kitchen.
C. P. SNOW, The Search
There may be nothing new under the sun, but permutation of the old within complex systems can do wonders. As biologists, we deal with the kind of material complexity that confers an unbounded potential upon simple, continuous changes in underlying processes. This is the chief joy of our science.
STEPHEN JAY GOULD, Ontogeny and Phylogeny
It is only when we can see the world as a ladder, and when we can see man's position on the ladder, that we can recognize a meaningful task for man's life on earth. Maybe it is man's task--or simply, if you like, man's happiness--to attain a higher degree of realization of his potentialities....E. F. SCHUMACHER, Small Is Beautiful
Happiness goes like the wind, but what is interesting stays.GEORGIA O'KEEFFE
The Creation Myth, Updated:
A Scenario for Humankind
The fact that we want to know about origins may tell us much about the way our brains work. It emphasizes that we try to develop comprehensive schemes by which the antecedents of all events are explained and future events forecast. This characteristic separates us from animals almost as much as does language, to which of course our particular sort of modelmaking is related.
J. Z. YOUNG, Programs of the Brain
Anthropologists tell us that almost every culture, every primitive people, has a creation myth; for example, Adam and Eve. It is a story, repeated by word of mouth down through the generations, which attempts to account for human beginnings. Each creation myth is peculiar to the people who made it--and to their technology and folk wisdom at the time the myth was finally frozen by being written down.
The Cherokee Indians of the Great Smoky Mountains of North America talk of a creator who baked his human prototypes in an oven after molding them from dough. He fired three identical figures simultaneously. He took the first one out of the oven too early: it was sadly underdone, a pasty pale color.
Now, creators may not do things perfectly the first time, but in creation myths, their actions are always irrevocable--so the pale human was not simply put back in the oven to cook a little longer. It remained half-baked. But the creator's timing was perfect on taking the second figure out of the oven: richly browned, it pleased him greatly and he decided that it would become the ancestor of the Indians.
He was so absorbed in admiring it that he forgot about the third figure in the oven until he smelled it burning. Throwing open the door, he found it was black. Sad, but nothing to be done about it. And such were the origins of the white, brown, and black races of mankind.
It isn't just the Cherokees who gently proclaim their own superiority: creation myths always assign the starring roles locally. "Imagine the Lord talking French! Aside from a few odd words in Hebrew, I took it completely for granted that God had never spoken anything but the most dignified English," exclaimed Clarence Day in Life with Father. And it is hardly surprising that we create in our own image, as creation myths have more to do with evoking one's revered ancestors than with satisfying curiosity.
The scientific subculture of the last 200 years has also developed a creation myth, though it undergoes major changes every decade or two as new ideas and new facts compete. Some scientific fields, such as anthropology and human ethology, might even be said to be in the creation myth business--in the sense that their goals are to improve on creation myths, to assemble a factual account of human origins. To make an analogy between the intermediate, imperfect scientific accounts and the creation myths is not to disparage either but to recognize one of the ancient origins of our scientific endeavor. And the analogy is useful in that it leads us to examine our scientific tendency to assign the leading roles locally: to the clever, the technologically innovative, the communicative--indeed, to those whom we might like to consider as our revered scientific ancestors.
That our casting for our creation drama reveals some subcultural nepotism does not make the conclusion wrong. It may nonetheless be true that the success of primitive technology and language helped brains to become bigger and bigger. But it would be nice to have another competing theory too, just to see if a more mundane explanation will do as well.
And what, one might ask, would constitute a satisfying explanation of things uniquely human? After all, if we are going into the creation myth business, we should take the talents of the storyteller into account. Good stories should be like well-planned gourmet meals--not just a tasty morsel, nor necessarily everything possible, but a palatable full-course meal.
We might expect one course to be the ontogeny, such as the neotonic slowing of development so that the puberty alarm clock goes off and starts to arrest growth while many juvenile features are still present.
And another element would be a natural-selection story such as the throwing theory, which relates genetic changes and selection pressures.
The timing would need to be just so, relating what had happened in the 6 to 10 million years since the gorillas and chimpanzees went their own way.
We might expect a satisfactory helping of language physiology, illustrating some of the natural subdivisions for language in those areas that are uniquely human.
We would expect some linguistics, showing the natural subdivision of language learning and use (which should go nicely with the known language physiology--but don't count on it).
The piece de resistance might be a nice mechanistic illustration of one aspect, something that you can really get your teeth into--such as a motor sequencing buffer being co-opted for language uses. Or maybe a special helping of human neuroanatomy, showing a unique set of pathways interconnecting hand motor strip and a temporal-lobe language area.
We would expect our satisfying spread to be garnished with other human specialites de maison, such as right-handedness and gestures and left-armed infant carry.
We would expect it to provide a sound foundation on which to build social and aesthetic (music, anyone?) theories, a vantage point from which to better understand human variability and special skills.
Hours later, would it still be a satisfying meal, or would there be hunger pangs? Some restlessness, of course, is a good sign, as we would want it to be a productive theory--to lead to better meals next time, rather than just being a fait accompli lingering in our memory traces. In the spirit of the artists who intentionally leave a small imperfection in a finished tapestry, we must never presume to have truly perfected our explanation.
This would be a left-brain meal, if it could be assembled at all--though that time seems to be approaching. A whole additional smorgasbord would need to be constituted to cover the other lateralized abilities predominant in the right brain: body image, visual-spatial, prosody, emotional faces, and such. Any such story is merely a selection from many facts and theories-- and it is always getting out of date. Still, trying one's hand at a creation myth is traditional, even if considered a sure sign of presenile dementia in some neurobiological circles.
We will pick up the story perhaps 15,000 million years after the Big Bang, during the most recent 0.2 percent of the lifetime of our universe. More than 50 million years ago, according to the fossils and the molecular-clock evidence, the New World monkeys went their own way from the Old World monkeys--literally, because the South American tectonic plate drifted away from Africa, the valley between them widening about 2 centimeters every year during the breakup of Gondwanaland. About 33 million years ago, the hominoids less dramatically took leave of the Old World monkeys, merely ascending into the trees. These proto-apes developed a brachiating way of life, which gives us and the apes a distinctive torso and shoulder structure unlike the monkeys.
Then the gibbon split off at 22 million years, to become the most graceful of acrobats. The orangutans split at about 16 million years. The gorilla split at about 10 million years ago. The chimpanzees and the hominids split off from a common ancestor about 5 to 7 million years ago, all this according to the DNA clock. Judging from the oldest hominid fossils, brain size back then was perhaps 350 cubic centimeters. There were an embarrassing variety of hominoid species by 1.8 million years ago, and in some the brain size was getting remarkably larger, starting the fourfold enlargement that is such an extraordinary event on evolutionary time scales.
There are many levels of "cause." The proximate source of the energy that your car uses to accelerate is the gasoline in its fuel tank. The ultimate source of that energy is, however, the thermonuclear energy released on the sun. Among the many intermediate "causes," such as photosynthesis, is surely the sandstorm that buried the swamp so that its rotting vegetation cooked underground at just the right temperature for millions of years so that oil deposits were formed. You could thank a different cause every day as you turned the ignition switch but it would be a month of Sundays before you started to run short of intermediate causes to thank.
To appreciate brain size arguments, one must be careful to understand that there are two kinds of "causes" in biology. Two extremes happen to correspond to medicine and to natural history, the two original endeavors which have gradually merged during the last century to become modern biology. The most familiar one to many of us is the functional cause: physiology is all about such mechanisms. When we ask about the "cause" of a bird's migration pattern, we can perhaps identify a change in hormone levels as the migration season approaches. Such a functional cause is also known as a~proximate" cause, in the sense of being the most immediate preceding event. Another kind of cause is distinguished in biology, often called the "ultimate" cause to place it at the opposite end of a spectrum of causes from the physiological ones. This is the cause of why one physiological mechanism exists rather than an opposite one, why a stay-at-home hormone rather than an emigration hormone, why one genetic program rather than another. Such ultimate causes have to do with ecological niches, natural selection, population dynamics-- with the operation of a genetic program throughout an evolutionary time scale.
Evolution operates in part by selecting for useful variants in intermediate causes. And one is a developmental trend called neoteny. Neoteny seems to be a general feature of higher primates, and is seen in exaggerated form in humans. Adult primates look progressively more juvenile. Their faces, for example, tend toward the flatter nose and the larger eyes (relative to the rest of the face) of the young. Juvenile appearance is often accompanied by a progressive slowing of developmental rates, so that it takes two years for a chimpanzee to grow as much as a monkey does in one year.
If we never grew up, of course, that would be the end of us. At some point, sexual maturity supervenes and growth usually slows to a stop soon afterward at some otherwise immature form by our ancestors' standards. It suggests at least two clocks keeping different time: one controlling growth rates, running slowly, and another controlling sexual maturity, slowed down but not quite as much. The pituitary gland's control of growth hormone is a traditional model for the first clock's mechanism (though one that has been much revised in recent years), and one candidate for the other clock is the pineal gland's control of melatonin.
But these are simply stand-ins for a more fundamental proximate cause, a matter that will eventually come down to alterations in regulatory genes. Indeed, it may be mostly minor changes in regulatory genes that separate us from the apes. We seem to share 99 percent of our DNA sequences with the chimpanzee and gorilla. Even our chromosomes, those protein backbones onto which the DNA strands are looped in a cell's nucleus like necklaces on a store's racks, look largely identical under a fluorescence microscope. Though the chimp has twenty-four chromosome pairs to our twenty-three, that seems to be because human chromosome No. 2 has enlarged to hold what is otherwise two separate chromosomes' worth of DNA in the chimp. The striking similarities suggest that a revolution didn't take place in the hominid line but rather something more subtle, a fine-tuning of sorts. Neoteny is just such a process. To adjust some developmental rate constants more than others would make the hominid phylogeny more analogous to manipulating interest rates in a complex international economy than to a political revolution.
It isn't just the shape of the face that results from neoteny. The adult head becomes larger, relative to the rest of the body. If you've ever seen a premature infant, you may have been shocked to discover that it was nearly half head (indeed, neurologists and neurosurgeons are always being consulted by premature parents worried about the possibility of hydrocephalis). In normal newborns, perhaps a fourth of the body is head. And while the head grows quite a lot in the first postnatal year, growth of the rest of the body outstrips it. If relatively bigger adult brains are a good thing, as determined by selection pressures, then neoteny is a genetic trend that could be reinforced. About one-seventh of the adult body is head--but it used to be even less.
There are some problems with retention of juvenile features, not the least of which is getting the infant head through the relevant portions of the adult female pelvis. One solution seems to be a somewhat premature delivery date, with the infant born even more helpless than usual, even before the skull is fully formed (that soft spot called the fontanelle). Some would consider much of the infant's first postnatal year to be equivalent to the last months of gestation in other primates. Another problem is the loss of body hair: juvenilized adults may have less body hair, an important matter to primate infants who cling to maternal hair for transportation while mother goes about making a living. And with the infant's state of development at birth becoming even more helpless, mothers must become even more skillful at carrying while gathering.
Problems, yes, but also advantages: more brain, relative to the body it must run. And a more flexible brain at that, retaining such juvenile features as curiosity, play, and a willingness to try out new things. Which may have been far more important than bigger brains per se. Juvenile primates are preprogrammed to learn by imitation of others (a feature which is most impressive in human children who, unless deaf, will automatically learn any language to which they are exposed). The long childhood presumably evolved because it made for more adaptable adults, more capable of behaviorally molding themselves to the environment in which they found themselves rather than just into the traditional niche occupied by their ancestors. This is handy for adapting to a changing world (the Pliocene and Pleistocene) and for expanding the range, to occupy a variety of habitats outside the tropics.
It is thought that upright posture evolved from this background much earlier, before 3 million years ago, perhaps from a hairless mother's need to carry her more-than-usually-helpless infant. But if infants can be carried, so can food. Instead of consuming it on the spot, food can now be carried back to a nest. In the same manner that birds and wolves bring home the bacon, so too could an omnivore hominoid. And not just a mouthful at a time (or a stomachful, for those species that regurgitate food for their young), but an armload, particularly important for foods lower in calories than meat.
And pairing, also common in birds and wolves, could have become an important survival trait: there would be two adults feeding the young, rather than just the mother. Many species manage without pairing, but for higher primates, a little help is most important. Even the modern-day great apes, who stick to lush tropical forests where making a living is easy, are just marginal when it comes to reproducing their kind (even without the depredations of human civilization). The long childhood means that chimpanzee births are spaced perhaps five to six years apart (a young chimp may nurse for four years), as the mother simply cannot effectively care for more than one child by herself. Even with a fifteen-to twenty-year reproductive period, getting two offspring to survive until reproductive age is hard for a mother to achieve, given the infant mortality. This extreme parental investment in a few offspring is the far end of "K selection" reproductive strategies; rather than using a shotgun approach like frogs, such species specialize in the well-aimed single shot. It is thought that the great apes may have overspecialized themselves toward extinction.
Only with the additional investment of the father's energies does the shorter human spacing between children become possible. But how did that come about? Like cooperation, paternal investment may be good for the species but not to the immediate advantage of any one individual (a male reproductive strategy for maximizing offspring known as "love them and leave them" achieves quantity at the expense of quality). Chimpanzee males, for example, probably do not know which infants they sired; while such behaviors as guarding the troop are useful to all infants, the chimp male probably cannot selectively boost the chances of some particular infants so as to help perpetuate his particular genes.
So how was some male help recruited? It is thought that the continuous female sexual receptivity, quite different from primate estrus, is a hominid characteristic related to solving this K-selection problem--essentially, attracting the male to stick around and, just incidentally, help care for his offspring. Such reproduction considerations, as Owen Lovejoy has pointed out, may well have been what set the stage for the upright posture and carrying. And they may be one reason that the hominid line has flourished better than the chimpanzee and gorilla line.
Thus the background to the great encephalization seems likely to include neoteny, upright posture, and pair-bonding. Encephalization must be judged by comparison to other animals, whose brain size varies with body size. A log-log plot of brain size versus body weight has a nice straight line running upward at a slope of two-thirds; double the adult body weight, and the brain will enlarge about 59 percent just to run the larger body. Most vertebrate species plot somewhere close to this line, and the neotenized monkeys and the great apes are somewhat above it. But humans are way off the line with nearly four times the brain volume of comparably bodied great apes.
There is no mention of handedness, language, or hunting in this sketch of our ancestors millions of years ago. Yet the picture differs from our present-day cousins, the great apes, in several aspects: upright posture, pair-bonding, and the lack of both hair and estrus. Compared to chimps or gorillas, ours was a better base from which to overcome the extreme K-selection of the higher primates (though it seems unlikely that anyone rationally considered this little problem in ecological economics!). Perhaps our ancestor was capable of living in more widespread habitats than present-day great apes, and perhaps there was some difference in the extent of neoteny. But there is nothing to say that this ancestor was smarter or better-spoken than chimps and gorillas.
The oldest of the fossil skulls from Hadar, in the Afar triangle of Ethiopia where "Lucy" was found, is more than 3 million years old and suggests a brain size between 370 and 450 cubic centimeters, right in the chimp-gorilla brain size ballpark. But something happened 2 million years ago: the hominid brain began a sustained growth and tripled to attain its present 1400 cc average size. Leading, of course, to the inevitable threshold arguments about "how big does a brain have to be if it is to have human capabilities?" which I shall spare the reader. Crossing this Rubicon (alleged to be between 700-800 cc) borrows another doubtful metaphor from physics, that of the chain reaction which, once a certain critical mass is achieved, takes off on its own. Personally, I'd say that 473 cc was the important threshold for brain size (I will break my rule against nonmetric units only long enough to note that this achieves a pint-size brain).
We also differ from the great apes in the extent to which we make use of hunting, language, and tools. General intelligence is often invoked, but that is harder to evaluate and it tends to turn the question around. We should ask first what encouraged that bigger brain up to the point that size became a virtue unto itself (if it is--certainly in present-day human adults, there is no correlation with "intelligence" as brain size varies normally between 1000 and 2000 cc).
And so we ask what, given the background sketched out above, is there about hunting, language, or tools that especially interacted with brain size? Other animals hunt and carry meals home to a family. Other animals use tools and even make them to a pattern. And chimps are certainly clever enough to make use of many elementary tools. Other animals use elaborate systems of vocal communication. What, in any of these, is there that could become so successful? Successful in making humans the most widespread and adaptable of animal species (hopefully we will retain this title, rather than passing it on to some radiation resistant insect that thrives on a radiation-resistant grass), successful in selecting for bigger brains?
The usual picture pieced together (the "hunting hypothesis") has all three interacting during group hunting of large game animals: the band of hunters using communication and strategy to corner a prey animal, then using tool-sharpened spears to pierce its tough hide, cutting tools to carve up the animal, and scraping tools to save its hide for clothing. Which we might call the Sergeant-Pepper's-big-game-hunting-band metaphor.
But is it reasonable to look upon this social-hunter metaphor as representative, back when brains were a third their present size? Solitary hunting as an adjunct to gathering seems a more reasonable first step, using strategy to succeed rather than size or speed. Tool use, as when chimps hammer open nuts with a handy rock, seems an earlier step than spears. And the spear throwing used by the hunting band must itself have precedents, intermediate between that advanced form and the unaimed throwing used by chimps in threat displays.
The communication needed to corner a prey, on the other hand, may be no greater than that used by chimps when they cooperatively corner a small monkey for a meal: they become quiet, take up alert postures, and move to block escape routes. They obviously accomplish a lot with body language (much as do modern-day hunting bands, even those encumbered with technology such as army patrols quietly probing enemy defenses). So elaborated verbal communication for hunting seems unlikely to engage selection pressure for bigger brains, at least when starting off from the biological base that existed a few million years ago. Body language seems sufficient for the task.
Body language, like its elaboration, the sign language of the deaf, does not have a prominent syntax, an ordering of signs that is important for deciphering the meaning. For the hominid precedents to our sequential ordering of otherwise meaningless sounds used in verbal language, we perhaps need a very sequential behavior of some kind to provide the foundation, the right neural machinery.
In more than one chapter of this book, the throwing theory has been put forward to illustrate how hunting could have suitably engaged the selection pressure ratchet in favor of both sequencing machinery and bigger brains. While intended as more than a metaphor, the throwing theory is but one example of a "fast track" possibility, standing in contrast to the generalized intelligence theory which says that brains beget bigger brains because intelligence is good. To say that throwing provides a fast track is not to deny other important elements of hominid evolution such as the carrying basket or the two-parent family; it is only to focus on a feature that could be associated with rapid encephalization. Whether or not throwing turns out to be the fastest track of all, something mundane may be primarily responsible for our most prized human abilities.
This should come as no surprise, but it does. Our present-day world is full of examples of sophisticated abilities arising in a short time from humble beginnings. In less than forty years since computers started pointing antiaircraft guns and breaking ciphers, the same types of circuitry have given us word processors and sophisticated examples of artificial intelligence. Not to mention all the smart toys for the kids.
New uses for old things--that is a theme in biological evolution as well as in modern technology. Feathers made good thermal insulation; when reptilian forelimbs had enough such thermal insulation, it probably became possible to glide downhill. Which, because it made catching flying insects easier (or some other utilitarian reason), promoted even more varieties of feathered animals. To identify the graceful flight of birds with more mundane beginnings is not to denigrate it but to better appreciate how evolution builds sophisticated capabilities step-by-step.
Humans are the product of a hominoid ancestor, shared with the great apes, and a unique series of selection pressures and ecological opportunities. For about the first 4 million years of separate evolution, both hominids and apes seem to have remained confined to Africa. But for much of the Pleistocene, hominids expanded outside the tropics. They were especially exposed to the selection pressures accompanying the changes in climate. Each Ice Age has also served to geographically isolate tribes of hominids, probably promoting inbreeding and speeding specialization on the fringes of the main population. The arctic ambience every 100,000 years has left behind an amalgam of abilities, producing a capital investment on which we have been living ever since. Increased skills in hunting, both in herding strategy and in projectile predation, surely occurred. And the improving rapid motor sequencer used for throwing could have also been used for speech--perhaps at special off-hours low rates.
Democritus and Aristotle thought that chance and purpose were the only two alternatives to explain life on earth. Scientists used to focusing only on proximate causes often continue to get hung up on that traditional dichotomy, even some Nobel-winning molecular biologists (and, alas, neurophysiologists as well) who pontificate on origins. But for more than a century, there has been another alternative: the Darwinian Two-Step (variations, then natural selection, alternating back and forth), an ancient dance where the changing environment automatically shapes new species from old, producing a stratified stability, a hierarchy of proximate causes.
And more recently, we have learned about the occasional sidestep~how novel uses are made of old things, so that unexpected things (like flight) arise from prolonged environmental selection for something else (like keeping warm). The human capabilities that allow us to read and understand this sentence -- neural machinery that must have existed for a long time before writing found a new use for it a mere 5000 years ago -- had an evolutionary history too, one that involved many stepping-stones and unexpected sidesteps. Surely one of the highest uses of our intellectual abilities is to understand how they evolved.
The Throwing Madonna:
Essays on the Brain (McGraw-Hill 1983, Bantam 1991) is a group of 17 essays: The Throwing Madonna; The Lovable Cat: Mimicry Strikes Again; Woman the Toolmaker? Did Throwing Stones Lead to Bigger Brains? The Ratchets of Social Evolution; The Computer as Metaphor in Neurobiology; Last Year in Jerusalem; Computing Without Nerve Impulses; Aplysia, the Hare of the Ocean; Left Brain, Right Brain: Science or the New Phrenology? What to Do About Tic Douloureux; The Woodrow Wilson Story; Thinking Clearly About Schizophrenia; Of Cancer Pain, Magic Bullets, and Humor; Linguistics and the Brain's Buffer; Probing Language Cortex: The Second Wave; and The Creation Myth, Updated: A Scenario for Humankind. Note that my throwing theory for language origins (last 3 essays) has nothing to do with the title essay: THE THROWING MADONNA is a parody (involving maternal heartbeat sounds!) on the typically-male theories of handedness.
Many libraries have it (try the OCLC on-line listing, which cryptically shows the libraries that own a copy), and used bookstores may have either the 1983 or the 1991 edition.
- Powell's Books in Portland lists used copies in their web database.
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