The Calvin Throwing Hypothesis

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    Almost as soon as Charles Darwin and Alfred Russel Wallace introduced it in 1859, the theory of evolution by means of natural selection raised the question of how humans evolved from an ape resembling a chimpanzee. Though many people disliked the theory (and many still do), the fact remains standing that if we accept the idea that the organisms that comprise Nature have evolved over time, from simpler forms to more complex, and if we accept the idea that Homo sapiens exists as a part of Nature, and not something apart from Nature, then we must accept the idea that humans evolved from a simpler, more primitive creature, something that would look very much like an ape. In particular, that remote ancestor would have borne a strong resemblance to a chimpanzee or an orang-utan.

    But by what steps did the ape evolve into the human? We look at how we differ from apes and we discern that humans differ from apes in two major ways. First, humans walk upright on two legs and cannot comfortably walk on all fours. Apes can also stand on their hind legs and walk bipedally, but they do so clumsily and prefer to walk on all fours. And second, humans have brains much larger than those of apes. We take that fact as the sine qua non of our humanity; although apes can display considerable cleverness, they cannot display full sentience. As far as we can tell, the property of sentience, of the capacity for abstract thought, belongs only to Homo sapiens.

    The question of human evolution then eventually boiled down to which came first, upright walking or the enlarged brain? That question got its answer in November of 1974 when Donald Carl Johanson (1943 Jun 28 -- ?) and his team dug up the incomplete skeleton -- the team recovered about forty percent of the skeleton -- of an australopithecine ape they named Lucy. The skeleton showed that six million years ago at least one species of ape walked upright, as we do, and yet had a small brain. That ape, Australopithecus afarensis evolved, in time and through several intermediate species, into Homo erectus as far back as 2,600,000 years ago. Existing from 3,900,000 to 2,900.000 years ago, the Southern Ape of Afar had a brain volume that ranged from 375 cubic centimeters to 500 cubic centimeters. That ape-like hominid, or one similar to it, then evolved into Homo erectus.

    In Homo erectus, which existed between 1,800,000 and 500,000 years ago, the brain grew from 850 cubic centimeters to 1100 cubic centimeters, overlapping the brain size of Homo sapiens (at the low end of the scale). Little change in the size of Homo erectus skulls occurred in the first million year, until about 800,000 to 700,000 years ago, and then changes occurred in the head to accommodate a larger brain. By 400,000 years ago Homo erectus was well on the way to evolving into Homo sapiens.

    In the late 1970's William Calvin (1939 Apr 30 -- ?), a neurophysiologist who teaches at the University of Washington, Seattle, began to develop a new hypothesis about how the hominid brain could evolve to a larger size. He noticed that humans devote an inordinate amount of attention to throwing things (think of our most popular games) and that a human throws farther and more accurately than any other ape does. We understand that the reason for that fact stands on the number and complexity of the neural connections in the human brain relative to those in the brains of other apes. With our large, complex brains we can coordinate the precise firing of hundreds of neurons controlling the muscles in our arms and bodies in a way that, even without feedback, we can throw a rock and hit whatever we aimed to hit. The other apes, with their smaller, simpler brains can't do that.

    So long and accurate throwing requires a large, complex brain. But Calvin turned that statement around and proposed that a life-style based on throwing rocks led to the evolution of the big brain. Here again we have an example of natural selection taking good enough and perfecting it.

    In the virtual reality simulator that lurks inside your giant brain imagine a scene from the beginning of the Pleistocene Epoch. By about 1,800,000 years ago our protohuman ancestors had already added meat to their diet, obtaining it from carcasses left by predators. They had discovered that meat and bone marrow taste good, that eating those things made them feel better and stronger, that eating meat and marrow diminished significantly the amount of plant matter that they had to eat, and that eating meat and marrow, if they got enough of it, made their children grow bigger and stronger. Those people stayed alert for any meat that they could grab. So imagine a family of proto-humans out foraging on the savannah of Ancient East Africa; imagine that they see a freshly killed carcass with the big cats that brought it down still feeding on it. The ape-folk don't dare to approach the carcass in that circumstance; they can only stand and watch the cats devour the meat as hunger and yearning mingle with frustration and, increasingly, anger.

    I understate the case when I say that apes don't control their emotions well. Jane Goodall has noted that on many occasions she has witnessed chimpanzees reacting to a rainstorm by crouching under whatever shelter they can find, stoically enduring their misery, while at least one member of the troop goes on a screaming, shrieking rampage, swinging from low-hanging branches, tearing up grass, throwing anything that comes to hand, and generally throwing a major hissy fit at whatever has come into the sky to piss on the troop. We can say with some confidence that our common ancestor with the chimpanzees did much the same and, since we still do very much likewise (note the behavior of spectators at sporting events), we can assume that our remote protohuman ancestors did so as well.

    In the scenario above, then, we can imagine at least one member of the protohuman troop fidgeting and fussing and then, losing all control, picking up a rock or a clod of dirt and throwing it at the cats. Of course, the rock only hit the ground, but the sound of the impact startled the cats and the vultures and other carnivorous birds gathered around the carcass. Noticing that reaction, the other ape-folk picked up whatever objects came to hand and threw them at the cats. The birds panicked first and only added to the confusion in their frantic flight from the scene. Emboldened, the ape-folk advanced on the carcass, still throwing whatever they could pick up and screaming and hooting at the cats. Having never encountered such a strange phenomenon before, the cats did what any prudent animal would have done in that case: they retreated and left the scene. The ape-folk then moved in and took over the carcass, getting for themselves all the meat and marrow they wanted.

    They didn't succeed every time they tried to rob a pack of predators of their kill, but they succeeded often enough that the practice of throwing rocks became part of their permanent repertoire of behaviors. For tens of thousands of years, then hundreds of thousands of years, the ape-folk kept this practice as a tradition. Over spans of time longer than our civilization has existed the dry, grassy savannahs of Africa served as a stage upon which these dramas played out. This practice of throwing rocks to clear cats off carcasses did not cause the ape-folks' brains to grow: It simply changed the environment into one that would promote any mutation that produced a larger brain.

    Then one child came into this world bearing a mutation that made his brain grow a little bigger and more efficient. At first no one noticed anything different about that mutant, but when he became old enough to participate in carcass raids something wonderful happened. Little by little that boy's throwing improved beyond what others could do. That boy could throw farther and more accurately than anyone else in the troop. Perhaps he could even hit a cat with a rock.

    Note: I have assumed that the first such mutant was a boy, rather than a girl, in order to simplify the case. Certainly the first such mutant could as likely have been a girl as a boy and certainly both boys and girls carried and manifested the mutation when it had spread throughout the population. I make the assumption more for my own story-telling convenience: Had the first mutant been a girl, the reproductive spreading of the mutant gene part of the scenario that I describe would merely have been delayed.

    With his special ability, Strong Arm could have driven cats off carcasses that his family could not previously have taken, thereby bringing more meat and marrow to his clan. Although he certainly would not have made the pitching lineup even in the minor leagues, had baseball existed in the Pleistocene, he would have had the status of a star among his contemporaries. And he would have, as a consequence, received a tremendous amount of female attention, as sports stars still do. Thus, the mutation that gave him his special ability would have spread rapidly throughout the protohuman population.

    As we expect, that process occurred gradually. First a mutation came into the DNA of one individual, giving that individual an enhanced throwing ability. That enhanced ability gained its possessor extra sexual attention, which spread the mutation throughout the population, preparing it to accept the next mutation, whenever it happened. Tens of thousands of years elapsed between such useful mutations, but eventually they added up to a new species, the precursor of Homo sapiens, if not Homo sapiens itself.

    In that span of time, as the collision between India and South Asia raised the Himalaya Range and erosion of those sky-striving mountains pulled carbon dioxide out of the atmosphere, the world grew cooler and dryer. Ice ages began to come and go, pumping the Malthusian life-sifter. On the dry grass-lands of East Africa the cycle of feast and famine made proto-human populations grow and collapse, each collapse leaving behind those who could best survive the famine, those who could best acquire the meat that they needed to survive.

Stealing other animals' prey does not provide anything like a reliable source of meat, so in the next stage of development late Homo erectus or early Homo sapiens began to kill their own prey. Of course, they couldn't kill the animals directly: they had to do something clever.

    In "The River That Flows Uphill" Dr. Calvin describes what he calls a "killer frisbee". It consists simply of a large pebble or small cobble that has had three or four pieces whacked off of it to give it a point. The stone fits comfortably in the hand, as we should expect from a stone specifically so altered that someone could throw it easily and inflict a lot of hurt upon some unsuspecting animal.

    I actually have one of those special throwing stones, one that I picked up in the Negev Desert about one mile west of Beer-Sheva in February 1972, when I visited the State of Israel. When I picked it up I noticed immediately how snugly it fit in my hand. The books I consulted later identified it as a Mousterian knife, but it didn't feel like a knife; the edges seemed much too dull. Now when I hold that stone in my hand, feeling its heft and its snugness in my grasp, I understand: Calvin got it right and my Paleolithic knife now appears to me as a missile. Somebody, a very long time ago, shaped that stone for the purpose of throwing it at an animal.

    Calvin has noted that archeologists have found many such stones near waterholes in Africa. That fact tends to support Calvin's hypothesis that Homo erectus or Homo sapiens troops came to waterholes, where herds of animals gather, in order to use a flock of thrown rocks to bring down some individuals in the herd while at the same time instigating a panic in the animals that sends them into a stampede. In the stampede, those animals that crouched down in response to rocks striking their backs got trampled and lay helpless as the hunters came to finish them off and harvest the meat and other goodies from their carcasses. Again, those individuals who could throw the farthest and the most accurately got plenty of special attention and the human brain grew incrementally larger in consequence.

    Now we must ask What does the ability to throw rocks accurately have to do with what we call intelligence? Yes, it created the large brain that we need. But how does a brain that evolved for throwing develop the ability to think abstractly?

    Let's begin by looking at one other feature of human intelligence that needs explanation. Researchers have found that no other animal, even other apes, understands pointing. If you do something interesting, a chimpanzee will mimic you; if you point to something, the chimpanzee will ignore you. And yet humans respond to pointing. Even small children can go beyond the "Look at me!" to the "Look at that!" and they will even initiate points to direct other people's attention to something that interests them. Whence did that ability come?

    If you throw something, such as a stick or a ball, many animals will follow the object with their attention, especially if that something relates to food. If you throw an orange, a chimpanzee will go after it. So now we know that throwing something can redirect an animal's attention. It would certainly have done so with our remotest ancestors: they would have followed with their eyes the thrown rocks as they flew to their targets. Eventually the gesture of throwing would become confused with the target of the throw, would come to signify an abstract throw at that target, one meant to direct another person's attention.

    When you point at something you put your hand and arm into the same orientation that they manifest at the end of a throw, with both arm and hand extended toward the target. So we can conceive a point as the abstraction of a throw. Note that when some people get sufficiently excited about something, they wind up and pitch their point.

    But how did we get from animals who don't follow a point to people who do? How would natural selection produce such a trait? We need to take great care in reasoning out the origin of this feature of human nature, because in this instance we have a temptation and a tendency to create a Just-So Story. Whatever we conceive in this case must have a clear genetic basis and it must create in the actual organisms a differential survivability upon which natural selection can act to alter the proportions of the genetic marker in the population.

    We know that the sight of a fast-moving object draws the attention of almost any animal we can name, so we can reasonably infer that the instinct to look at fast-moving objects has a genetic basis. That inference makes good evolutionary sense because any animal that did not become aware of fast-moving objects quickly had a lower likelihood of surviving than did an animal that did attend to the rapid motions of possibly dangerous things. So when our ape-like ancestors threw things, the ape-folk around them had the instinct to watch the thrown objects.

    We add one other factor here and note that primates can do what no other animal can do: we can reach for things and grasp them in our hands. Reaching can also give us a model for redirecting another person's attention if that other person can anticipate what we reach to grasp. And reaching involves essentially the same extended-arm/outstretched-hand gesture that throwing does.

    So we know that proto-humans had the instinct necessary to redirect their attention when someone extends their arm. We now face the trickier task of determining what environmental pressures would have promoted any mutations that extended that instinct onto more abstract targets. How would the ability to get a point enhance an individual's reproductive ability?

    East Africa has never given humans or their semi-ape ancestors a safe place to walk. Under the right conditions, even today, lions will attack, kill, and eat humans. Those conditions consist essentially of too many lions for their normal prey, due either to an excessive increase in the number of lions in an area or an insufficient increase in the number of prey animals (zebra, wildebeest, etc.). Our ancestors had only one effective defense against a lion attack -- running.

    It may seem absurd to posit the hypothesis that our ancestors could outrun a charging lion. But consider an old joke:

    Two men out hiking in the mountains see a bear charging down the trail at them. One man immediately drops his pack and removes his heavy hiking boots. The other says, "Surely you don't think you can outrun a bear!" The barefoot man takes to his heels and yells back, "I don't have to outrun the bear. I only have to outrun you!"

    That joke plays subtly on an odd fact. Humans don't run fast, but we have tremendous endurance. We display that endurance in marathon runs, the 26-7/32 mile runs inspired by the achievement of Pheidippides during Battle of Marathon in the war between Greece and Persia in BC 490 September. The fastest runners actually maintain an average speed of about thirteen miles per hour for two hours. So we can see that, given a long enough head start, the average human can outrun any predator in Africa, even though the predators run faster: although they have superior speed, predators can only apply their high-energy runs for short intervals of time. When the charging lion has run out of energy, the humans just keep on going.

    So now we can derive an hypothesis from the bear joke. Imagine an extended family of Homo erectus wandering across the savannah, foraging as the go. They don't want to get to far from each other, but they also don't want to come close enough to their neighbors that they will get into fights over whatever food they find. So they spread themselves over a small area. Suddenly someone sees a lion stalking the group, shrieks out an alarm call, and then either throws something at the lion or mimics doing so. Perhaps that person made the throw to emphasize the presence of the predator or perhaps they simply did it out of habit based on using thrown objects to clear lions off carcasses in better times. Other members of the group follow the throw to the intended target and take off running in the appropriate direction. One member of the group does not get the point, but responds to the alarm call by looking at the alarmist and then looking around for the lion, spending extra seconds before spotting it and also running away from the lion as the lion charges the group. That person ends up bringing up the rear of the running group. If the group has not had a sufficient head start, that person becomes lion food and thereby enables the others to escape more surely (have I mentioned the sheer Malthusian cruelty of evolution lately?). In this way the proportion of people who do not get a point diminishes in the population over time, which results in a human species uniquely equipped to get an abstract point. In this case we have not so much selection (especially sexual selection), as Darwin said, but more of a process of elimination, as Wallace said.

    And let's not forget to consider the yelling and screaming with which chimpanzees accompany their throwing of rocks at predators. Those vocalizations evolved into language, the ultimate abstraction of pointing and the basis for our intelligence. As the hominid brain grew larger and more complex it grew able to make finer distinctions in sounds as well as to create sounds based on finer distinctions.

    Again natural selection acted on a pre-existing structure, reshaping it to carry out an extension of its original use. Almost all mammals make noises with their mouths and throats, from growls to howls. Typically they use those vocalizations to express various emotional states B fear, contentment, anger, distress, etc. B that others in the group then feel. As the hominid brain grew the repertoire of possible calls grew with it.

    Just as vervet monkeys have different panic calls to represent danger from eagles, jaguars, and snakes, so our remote proto-human ancestors likely had a repertoire of calls representing different dangers. Natural selection works well on that kind of phenomenon; those who made and responded to such calls avoided feeding the predators and those who didn't respond to such calls led the predators' menu.

    As proto-humans evolved larger brains and, with them, the ability to make finer distinctions in sound, they found that they could make calls to represent finer distinctions in dangers. Eventually they would have devised calls for anything that made a strong impression upon them: vervet monkeys don't, for example, have a call for lightning; Homo erectus likely would have had one. Lightning, thunder, flood, fire, stampede -- words like these would have come early into the proto-human vocabulary. Waterhole, trees, river, hill -- these would also have come early into the vocabulary due to their importance in the day-to-day survival of the group. The hearing of a word would conjure in each person's mind an image of the thing the word names and thereby evoke the appropriate response.

    Like throwing, speaking didn't have to begin with all the finesse that we give it. Homo erectus conversation likely would not impress a modern three-year-old child. But the ability to go away from the group and then come back and report on what they had seen would have given the ape-folk an advantage over those who could not do so: it made their hunt for food and avoidance of predators more efficient. Those who could articulate best, usually also the best throwers, would have given their group the best advantage and, thus, would have gained more sexual favor, thereby ensuring that their genetic coding came to dominate the species over time.

    Using pointing and speaking together enabled the proto-humans to build up vocabulary, to create words for things that don't evoke strong emotions. They could begin to talk about things that had nothing to do with the immediate need to find a meal or avoid becoming one. They gained the ability to share their experiences and their observations of the world and thus enlarged their knowledge of it. And they gained the ability to do things that no animal had ever done before, things that no mere animal could do.

    Thus a rather excitable ape that walks upright began throwing things at predators to gain access to meat. That practice promoted those mutations that enabled more accurate throwing. The larger and more complex brain that resulted from those mutations also gave the ape-folk a larger repertoire of calls, which grew to such an extent that the people could share their thoughts with each other. The beginning of language made the ape-folk human in the same sense that we are human. Once they gained the means to express their thoughts, and thereby to expand them through social interaction, our ancestors began to free themselves from their dependence upon blind evolution. Once they began to think of things never before seen, those people began the long struggle to create civilization.

    How can we claim that this story does not represent a Just-So Story? On what basis can we claim William Calvin's throwing hypothesis as a plausible explanation for the evolution of modern humans from upright-walking apes? We have a list of features characteristic of a Just-So Story, so we compare our scenario against that list:

    1. We have not assumed in our ape-folk any behaviors that naturalists have not seen in animals in the wild. For example, naturalists have witnessed the origins of what we can call culture in other primates. One famous example of that comes readily to mind:

    Beginning around 1952 Japanese researchers began leaving sweet potatoes on the beach on the island of Koshima, off the north coast of Honshu, for the macaques (Macaca fuscata) who lived on the island. Soon they noticed that one female, whom they named Imo (sweet potato in Japanese) would take her potatoes to the shore and dip them in the water. Soon Imo's playmates began to mimic her behavior and then Imo's mother. Eventually all members of the troop except the oldest had adopted the habit of washing sand off their sweet potatoes instead of brushing it off. They even continued to dip the potatoes into seawater as they ate them, apparently for the added flavor of the salt. That behavior persists in the troop, even though Imo and her friends died a long time ago. Thus we see that simple Monkey See, Monkey Do learning can create a simple kind of culture in primates and we can infer that the same effect operated in our remote ancestors when they began throwing rocks at lions and hyenas.

    2. We have not assumed that throwing made the human brain grow larger and more complex. Even if practice made one person throw better, that person would not have passed that improved throwing ability on to their offspring; they would have passed on only the ability to learn to throw better. In accordance with the theory presented by Charles Darwin and Alfred Russel Wallace, we have merely asserted that a culture of throwing provided the condition that promoted any mutation that increased brain size and complexity, but did not produce the mutation itself. Thus we reject any statement that has a life-form passing on to its progeny any trait that it has acquired by direct interaction with its environment.

    Further, we have not assumed the occurrence of a magical mutation, one that came "out of nowhere" for the sole purpose of verifying our hypothesis. We already know that mutations that change brain size and shape have occurred frequently in the past. We know that fact because we know that mammals, which evolved from fish, have larger and more complex brains than fish do.

    3. We have not assumed that the ape-folk had any intention or anticipation that their behavior would result in the evolution of increased throwing ability or intelligence. Homo erectus simply lacked the ability to plan that kind of change. The ape-folk took to throwing rocks at predators in order to achieve an immediate goal, that of obtaining food. Thus we reject any statement that imputes to non-human (or even proto-human) life-forms intention or foresight, any ability to plan or to seek goals beyond the immediate present. If we discern any phenomenon that resembles planning and we cannot explain it through simple Monkey See, Monkey Do learning, then we must interpret it as instinct and find an evolutionary explanation for it on that basis. In this case we don't need to do that.

    4. We must reject any statement that over-applies the theory of evolution. We must take care that we do not use natural selection to explain phenomena that we can explain in other, more reasonable, ways. In this case we may feel a temptation to hypothesize that in addition to promoting the evolution of our big brain, the throwing culture of our remote ancestors also promoted the evolution of women's interest in sports stars. That guess would take the hypothesis too far. We would have entered the realm of sociobiology, which many evolutionary biologists regard with justifiable suspicion.

    So can we say now that we know how human sentience evolved? Actually we can't; we can only accept the above argument as an opinion and not as knowledge, simply because we don't have evidence strong enough to ensure its truth to Reality. We have fossils, certainly, and Dr. Calvin's killer frisbees. Those items constitute strong evidence to support the scenario described above, but they do not necessitate it. So we accept the hypothesis only contingently. We take the attitude of waiting for more evidence. But until someone presents an alternative hypothesis and strong evidence to support it, we feel justified in accepting this hypothesis.



Calvin, William H.; "The River That Flows Uphill", 1986, Macmillan Publishing Company, New York, ISBN 0-02-520920-5


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