An Essay on Human Evolution


© 2005, 2006
Clyde M. Davenport
Updated 7/19/06, 2/21/10


Changing Climate

Pre-Human Primates

Running Strategy

Body Adaptations

Who Were They?

Emergence of Intelligence



The following is merely one laypersonís opinion and speculations on the conditions and processes that produced the first tool making, sentient, intelligent creatures that we call human. It addresses the period during the forest-savanna transition in East Africa and through to the first handaxe and spear making, a period of roughly three and a half million years (5-1.5 million years BCE). The author will propose some probable events that must have occurred in this period.

It is not generally recognized by the public that our pre-human ancestors went from among the weakest, most defenseless prey on the East African savanna to the predatory terror of the world, all in an interval of perhaps a million years. What happened? How did we do it? We were surrounded by vicious predators. We had no claws, no fangs. We couldnít dig, and there was not much to climb in that place and time. We were much smaller than we are today. We adopted a fragile, two-legged stance in a four-legged world. Clearly, we were not built for fighting, and we were inferior at running. So, how could this be?

Happily, much research has been done and far more is known about this than has been conveyed to the general public. The results are in the archaeology, paleontology, and paleoanthropology literature. It is available to anyone who cares to make the effort to read and understand. A very readable summary of the research findings is given by Stringer and Andrews1. We shall take several key ideas from Harris2. Although we shall rely heavily upon these two references, the particular interpretations and opinions, here, shall be due solely to the present author. I challenge the reader with the following question: "Do we really believe in natural selection, or not?" Top

Changing Climate

To begin, perhaps ten million years ago East Africa was heavily forested and well populated with tree-dwelling primates of a variety of types. Around five million years ago (at the end of the Miocene Epoch), the climate began to change from wet subtropical to much more arid, grassland conditions. Over about the next three million years, the heavy forest cover gradually died out, and it is in the late stages of this transition period that things become interesting. Our primate ancestors were forced down onto the ground, amidst the most brutal lineup of predators in the world. Lion, leopard, hyena, wild dogs, many in large packs. They are all still there today, just as they were. You may see them on almost any African wildlife show on television, literally ripping prey limb from limb. To get the picture that our ancestors faced, imagine yourself set out at night on the African plain among these predators.

An important set of facts to keep in mind while reading the following is this: Archaeological and paleontological research and field work have shown that bipedal primates first appeared in East Africa approximately five million years ago, roughly at the beginning of the transition from forest to savanna conditions. These creatures would face a difficult transition to savanna living. Some of the other animals would have difficulties, others not. The lions and leopards of the time had forest-dwelling predecessors who, being top predators, had no trouble transitioning to savanna living without having to modify their general body conformation and behaviors. Not so for the hyenas and wild dogs. Inasmuch as small, ground-dwelling predators in the present-day equatorial forest do not run in packs, we surmise that hyenas and wild dogs had to make many adjustments for grassland living. During the wet-arid transition, they might not have been a threat to our pre-humans, but as their pack behavior evolved, they would become a dire threat. We speculate that the cheetah was originally much smaller and more gracile. More on this, later. Top

Pre-Human Primates

So what would have our direct, pre-human ancestor looked like, at the point where the tree cover began to disappear? Let us begin our hypothesis. It couldnít have been a ground-dwelling ape. With the tree cover gone, they would have been too slow and clumsy to survive the predation of the big cats. Instead, we hypothesize a smaller, more alert, active and agile primate that looked something like a rhesus or capuchin monkey. Indeed, the first proto-human creatures (Australopithecus) were under five feet tall and had slender, thin-boned body types. On the ground among predators, such a creature would have flight as its sole defense.

The following bit came from the Sigma Xi American Scientist journal sometime in the early 1970s. In East Africa, paleontologists had excavated a sinkhole-like depression that they thought might have been a cave wherein early humans might have lived. Instead, they found large amounts of detritus that had fallen down from above, and scattered among this they found numerous pre-human skulls with few accompanying skeletal bones. They puzzled over this odd fact for some time, until they noticed that many of the skulls had teeth marks on them. After reviewing leopard behavior, it became clear what had happened. Late in the wet-arid transition period, only widely-scattered, small clumps of trees remained, those in low places in the terrain, such as around sinkholes. Leopards carry their prey up into a tree to eat, because otherwise the other predators would move in and eat not only the prey, but the leopard, also. With small prey, leopards consume everything, but the skull is slippery and difficult to hold onto. They tend to accidentally drop some of the skulls, thus their appearance in the sinkhole. Sure enough, when the paleontologists excavated other sinkholes in the region, they found the same thing. It is clear that we were once defenseless prey. Top

When our primate ancestors were first dropped into this sea of snarling teeth and fangs, they werenít completely bereft of any useful survival tools. Their tree-dwelling lifestyle equipped them with certain physiological characteristics that were useful then, and still are today in our technological world. First, they had excellent binocular vision because they had to precisely gauge how far away that next tree branch was before they could leap to it. Secondly, they had a large brain as compared to that of a ground predator. This was used to process the critical visual input and do complex body movements. They had superb balance and motion sensing. They had exquisite hand-eye coordination and body control, absolutely essential for moving about in the treetops. They were prodigious leapers. Their hands were designed for fine grasping and manipulating motions. They had the beginnings of reasoning ability, as do chimpanzees, today.

Running Strategy

Once on the ground, though, our primate ancestors had only two options: (a) avoid predators, and (b) run from them. For the first, they adopted a strategy that ran counter to intuition and opposite to that of other prey animals. Small prey animals tend to stay low and conceal themselves in the grass and brush. Our primate ancestors stood up in clear view of every predator for hundreds of yards around! A foolish thing, you say? Not really, because they could visually scan large areas for predators, accurately gauge their distances (remember the binocular vision?), and move in such a way as to avoid them. We surmise that they could even see competing packs of predators moving in and run in such a direction as to cause the predator packs to stumble upon each other and fight among themselves. It is not at all unreasonable to assume that early pre-humans thoroughly understood predator behavior and manipulated it to their advantage. We wouldnít be here if they hadnít. Top

Their plant-food diet compounded their problem. In the trees, they ate fruits and tender shoots. These items were in short supply on the ground and were concentrated around widely-separated sources of water or small clumps of scrub bush. Unfortunately, those were all places that the common predators sought for shade in the heat of the day. Tree-dwelling primates are diurnal creatures because of the simple fact that it is fatal to be swinging around in the treetops in the dark. We hypothesize that our ancestors remained so on the early savanna. Assuming so, then they had to continually move about in broad daylight in search of food, and they had to continually come into close contact with the most vicious of predators.

Clearly, our pre-human ancestors needed to improve their running skills if they were to survive. Fresh down from the trees, they were built neither for speed nor for endurance. Every significant predator could outrun them. Imagine chimpanzees out on the open savanna, today. We must conclude that in this period they were saved only by their superior depth perception, agility, and leaping ability, all needed for close-in avoidance motions. This may have been the lowest point in the pre-human population level, and predators could not have relied upon them as a staple. In fact, many predators might never have seen a pre-human and might have been confused by their odd behavior when they did. Top

We know that they had to run, so let us lay out some necessary running parameters. Suppose that you are a pre-human alone on the East African savanna in the heat of the day and you see a leopard stalking up and beginning a charge, intending to have you for lunch. He is faster than you, but you have seen him from perhaps 100 yards away. Now, a leopard can run at top speed for only around 200 yards before the heat of his exertion begins to slow him down. Accordingly, if you can detect him early enough and put on an all-out sprint for around 100 yards, he may get close, but you can match his speed and can begin to pace yourself. At 200 yards (300 for the leopard), you begin to outpace him. The leopard can continue to run only for around 400 yards total, then he must stop, or he will collapse into a coma from heat exhaustion and be vulnerable to other predators. You may be sure that our pre-human ancestors learned this simple fact, early on.

[Perhaps you missed something interesting in the numbers: an all-out sprint for about 100 yards, a strong sprint out to about 200 yards, and a strong run to 400 yards. Do you think it is a simple happenstance that the Olympic running events begin with 100, 200, and 400-meter sprints? I donít. Nor does it end there, as we shall show.] Top

Body Adaptations

Clearly, our pre-human ancestors had to evolve to survive running scenarios such as the above. The first need was for more speed and a change of gait. Observe chimpanzee behavior on the ground, today. If they must run, they do so on all fours, with kind of a gallop on their feet and knuckles. They are fast, but not fast enough for savanna living. Natural selection would have immediately emphasized longer legs for more speed and an even-more upright stance for earlier predator detection. Sometime in that period, the first truly human-looking creature stood upright and gazed out over broad grasslands. Stop for a moment and look at your legs, and contemplate this: they have that general size, form, and proportions because of the lions and leopards of East Africa.

There is another advantage to an upright stance, one more subtle but possibly more important for survival. Our pre-human ancestors could safely sprint and hurdle through thorny low bush country, simply because they were good leapers and could see over the obstacles. The big cats could not risk leaping over, say, a four-foot thorn bush for fear of landing in another, nor could they simply crash through because their eyes would be gouged out. Even on a flat savanna with only a single low thorn bush, a closely-pursued primate could make the predator lose half a step by simply hurdling over the bush. That could be just enough for survival. Top

[Is it just a coincidence that the Olympic Games include 110 meter and 400 meter hurdling events? And why, pray tell, these particular distances?]

Humans have exceptionally large buttock muscles (for a primate) that play a key role in straightaway running and sitting/squatting/lifting movements. This is well understood. However, they have another important function that is overlooked, today, because it seems inconsequential; that is, a large buttock muscle helps pull up and fold back the trailing leg so that effective hurdling is possible. It is entirely possible that humans would have been eliminated if they had not developed this capability.

What's that, you say? Big cats wouldn't be afraid of a few little thorns? Maybe not, but these aren't "little thorns." They are two inches long and as sharp as needles. To illustrate the respect and avoidance of them that is exhibited by the big cats and other predators, recall that pastoral tribes in Kenya secure their cattle and themselves at night in a small compound that is fenced by only tangled piles of thornbush cuttings. Despite the obvious concentration of easy prey, the big cats concede and move on. Top

These pre-humans did not immediately evolve a larger body size, and that fact, alone, is revealing. It emphasizes the fact that they needed quickness and agility for their basic survival. In particular, they needed quick reaction and a burst of acceleration in order to escape the close-in charge of a leopard or lioness. Today, we have grown far too large and clumsy to get away. At about the second step out of the blocks, we would feel the piercing crush of fangs.

The fact that such evolution could occur on such a short time scale, perhaps as short as a million years, depended critically upon the fact that tree-dwelling primates have an adaptable brain structure that enables and accommodates a wide range of body movements, perhaps the widest range among the higher animals, so that adaptation to a slightly different running technique was not that extraordinary. Also critically important was their highly-developed sense of balance and their precise body control, otherwise they could not effectively run on two legs. That their evolution took them to a more upright stance was due to the fact that there was an advantage to a higher point of view, yielding ever greater intelligence about stalking predators and allowing all-out hurdling through low thornbush. With longer legs, now they could sprint, probably with the best of them at the time. We surmise this because tree-dwelling primates have much stronger muscles, by a factor of five to ten times, than those of present-day humans. Just ask any primate caretaker in any zoo! No other non-primate creature on the savanna could change their running stance in this way because they did not (still do not) begin with the necessary adaptable brain structure and physiology. Top

We turn next to an adaptation that our pre-human ancestors either had when they came down from the trees, or may have evolved or enlarged upon early in the transition period. We refer to extensive brain-cell redundancy, an idea that we credit to Harris2. Recall the discussion, above, of a leopard on a pursuit run. We pointed out, and this is verifiable today, that if a leopard runs too far at high exertion levels, it will stagger and eventually collapse into a coma from heat exhaustion. It does so because its brain cells begin to fail above a certain temperature. They do not all fail at once, like a light switching off. There is a fading-out interval. Now, our pre-humans were subject to the same limitation, but they may have had an edge. No brain is strictly compartmentalized, for example, with a certain set of a million cells dedicated to only smell and nothing else. There is overlap, shared function, and redundancy. Just as for the Space Shuttle, redundant circuitry is more fail-safe. Today, we see that persons with certain types of brain injuries can actually retrain nearby segments of their brains to perform the function of the missing cells. Higher levels of redundancy occur in larger and more-evolved brains. All else being equal, brain-cell redundancy can delay heat collapse by some measurable time interval. In a life-or-death pursuit, even seconds can prove advantageous. It may be that early pre-humans could already sustain a full-exertion run farther than could their common predators. If not, natural selection would have strongly pressed for that ability. Indeed, we hypothesize with Harris that our larger brains were not initially evolved for their intelligence benefit, but for the simple ability to run farther! Top

Hawkins3 has developed a testable theory of brain organization, brain function, and intelligence that readily explains many of its astonishing abilities. Central to the theory is that it is not tightly compartmentalized by function. For example, motor control neurons are scattered throughout areas that predominantly process sight, smell, touch, and other functions. There is high redundancy. Loss of a few neurons in any one spot will not disable any given function. Human brain organization and function is just an enlargement and elaboration of that of the higher primates. The most significant difference is in the size of the neocortex, the thin outer layer of the brain, wherein rational thought and consciousness of self resides. At the cellular level, there is practically no difference. Hawkins contends that as the neocortex expands, more and more abstract associations can be made, eventually reaching a level of ability that we call intelligence.

Only one other tree-dwelling primate of that time, the baboon, made the transition to ground-foraging savanna life, and they used a different strategy. Apparently, they began with a much more aggressive mentality than our pre-humans. They decided to stand and fight. By this choice, they retained their basic monkey-like body conformation. Running would be avoided. In order to succeed, they had to evolve a fearsome set of teeth, powerful jaws, and cooperative defensive behavior. Even today, a lion or leopard might attack a lone baboon - but not ten. They form a phalanx, fangs bared, and make it clear that the attacker will get more than he bargained for. However, they cannot freely migrate about. They must have safe home ground with trees or rocky outcrops for protection at night. The next time that you see one on a nature show, you might truly say, "There, but for the slight rearrangement of a relatively few neurons some five million years ago, goes I ." Top

Our hypothesizing, here, could go quite astray if during the transition period there existed a superfast predator that our pre-humans could not have possibly outrun, even with early warning. Such a predator exists today on the East African plains: the cheetah. However, and this is important in a number of ways, genetic DNA studies show that all present-day cheetahs are descended from only a handful of individuals who lived approximately five million years ago. In other words, cheetahs almost died out while making the transition from deep forest to savanna living, so they were of little threat to our pre-human ancestors. While leopards are quite similar to New World, forest-dwelling jaguars, the cheetahís predecessor must have been a smaller, more gracile creature similar to the South American ocelot, whose sole option for survival would have been to run, and fast. Early on, they may have survived solely due to an ability to make a springing, darting, unpredictable run, much as does the present-day springbok and Thomsonís gazelle.

[We humans may share with the cheetah more than we realize in our species survival histories. Just as the cheetah has little genetic diversity because it went through a population bottleneck, so do we. Current thinking about our own case is that approximately 12,000 years ago, our population was down to less than 100 breeding pairs. This is based on DNA studies and estimates about how fast our genetic base mutates/evolves. The cause of our bottleneck is being vigorously argued, some candidates being ice ages, the Toba volcanic eruption, etc. However, what if our estimates of the rate of mutation of human genes over time is wrong? What if the current rate that we see applies only to modern man, Homo sapiens sapiens? Is it possible that our bottleneck was actually coincident with that of the cheetah, and for the same reasons?] Top

Thus did our early pre-human ancestors survive the transition to ground living and learn to cope with lions and leopards. However, they could not relax, because an even more dire threat was literally springing up around them. The cheetahs were gaining in size, numbers, and speed. The hyenas and wild dogs were evolving very effective pack-hunting techniques. We know that they had to evolve the behavior, because there is no chance that a pack of anything was going catch prey while thrashing around in the earlier forest environment. Unlike the big cats, who stalk and make a short sprint to capture prey, the pack hunters are tracking, harrying, deadly-persistent killers. There is essentially NO limit on how far they can run. They can go at a steady gallop for miles on end. They merely select a victim and run it and harry it until it collapses from exhaustion, then literally eat it alive. Hyenas, in particular, are brutally savage predators from the day that they are born. They come out of the womb with eyes open and a full set of teeth, and immediately begin fighting ferociously with their littermates, many times to the death. The jaws of an adult hyena can crush bone, and if an early human were victimized, he would be entirely consumed. Hyenas are so aggressive that a family group can easily stand off a pride of lions. Clearly, our pre-human ancestors were not prepared for this. What they did next, I can only contemplate with utmost awe. Literally overnight, on an evolutionary time scale, they again remade themselves in order to meet the challenge.

At this point in time, their most pressing need was for more running endurance. [If you were a genetic engineer and were charged with solving this problem, what changes would you make?] Their solution was to evolve the ability to sweat! [Harris2] By this stroke of brilliance, along with a dramatic increase in lung capacity, they greatly increased their running endurance. The evaporation of the sweat cooled their bodies and delayed heat collapse. No other animal on the savanna made this innovation, not even their close relative, the baboon. We hypothesize that a duel of running skills developed. As the cheetahs and pack animals improved their speed, endurance and hunting skills, our pre-human ancestors must have matched them stride for stride, foot race by foot race. We became marathon runners. Otherwise, we wouldnít be here to speculate about it. Top

The above view is supported by the structure and evolution of the human foot. As we went from A. Africanus to H. Habilis to H. Erectus, our foot structure went from largely ape-like, to intermediate, to distinctly human. Simply put, we developed a heel bone and an arched foot. It helped with balancing upright and carrying loads, but these benefits were incidental. The real gain was in efficiency of walking and jogging, both of which were needed for sustained, long-distance flight from predators. A sprinter largely stays on the front part of his/her foot at the expense of great muscular exertion, but a marathon runner puts each foot down evenly, and more or less glides along at minimum exertion.

The particular distance figure that our ancestors developed is extremely significant, and not only for its endurance quality. Clearly, a pack of hyenas or wild dogs could readily track a group of early humans for 26 miles or more, and almost certainly did. The real significance is that if an early human started from any point on a flat savanna and ran in a straight line in any direction for 26 miles, he/she would cross over into a different predator territory. As can be seen today, the savanna is divided up into an invisible patchwork of predator territories, and if one pack transgresses into a neighboring territory, it is in for a vicious fight. Homo erectus, clever as he was, would have understood these simple facts and would have exploited them. For example, suppose that a group of early humans are moving across a flat savanna and are bounced by the hyena pack that "owns" that territory. The humans do not run in some arbitrary direction. They know where the nearest neighboring hyena pack lays up in the shade for the day, and the humans head straight for it. The hyenas, who know where the boundary is and do not normally cross it, are overly excited by apparently easy prey, and cross over. Before they know it, they run right up to the second pack's lair, and all hell breaks loose. The hyenas would eventually come to associate those spindly-looking, upright creatures with a horrific, snarling fight, and would soon learn to leave them alone.

There may also be more to the evolution of sweating than we realize. This author has often wondered, "Wouldn't it have greatly added to the benefit of sweating if the sweat contained a strong scent component that masked all of our other body odors? That smelled like no prey item, whatsoever, and possibly was even repellent to predators, like a skunk's scent? Wouldn't it confuse and throw off a tracking predator? Could such a thing have actually happened?" Imagine the author's amazement upon learning of the genetic disorder trimethylaminuria. At least, it is described as a genetic disorder, implying that it occurred as an accidental defect in a human gene. However, that might be an entirely erroneous view. It might actually have originally been a beneficial mutation that was emphasized by natural selection, then was later suppressed because the original impetus went away. Let us examine that notion. [The basic facts in the following discussion were taken from Science News Online for May 15, 1999. The speculations are the author's own.] Top

When we examine the characteristics of trimethylaminuria, we see that it has dead giveaway written all over it. Most suggestively, the smell that it produces is a strong decaying fish odor, unlike anything any large predator would ever have associated with any food item upon the dry African savanna. Significantly, it does not smell like ordinary, offensive human body odor or decaying flesh, either of which would attract predators and scavengers from all quarters. Secondly, a molecular model of the flavin monoxygenase 3 enzyme (FMO3) that produces the odor compound shows that the modification from the normal enzyme is radical, affecting perhaps thirty percent of the structure. It doesn't appear that it is the result of an atom or two being knocked out or a link or two being rearranged. It does appear that this much modification would have required many generations to develop, meaning that it must have been beneficial at the time. Thirdly, the FMO3 enzyme operates on proteins in the human gut. This is significant because the adaptation was highly unlikely to have developed before humans began eating meat, which occurred not long before the time when early humans were under the greatest predatory pressure, around the time of the appearance of Homo erectus. Moreover, we know that they were already undergoing many genetic changes in order to obtain benefit from meat (see below). Top

So, assuming that trimethylaminuria occurred as a beneficial adaptation around the time of Homo erectus, why was it subsequently suppressed? By some counts, there may be less than 600 recorded cases in the present world population. There are several obvious reasons. First, humans developed effective weapons and removed the predatory pressure. The basic impetus for the adaptation was removed. Secondly, with the original impetus gone, now the adaptation was a liability. The smell was so overpowering that it interfered with normal olfactory function. Then as now, humans require a subtle and discriminating sense of smell to locate and evaluate the suitability of food items. Thirdly, after the adaptation was substantially suppressed in the population, such that it became uncommon, then it was even more rapidly eliminated. As we see even today, anyone with any unusual, strong body odor is socially ostracized and is less likely to produce offspring. Ergo, the adaptation was strongly suppressed, but has not entirely gone away. Perhaps those unfortunate individuals, today, who have trimethylaminuria can take some solace in realizing that it is not just some accidental disorder, but is quite possibly something to which all of us owe our very existence. Top

Another cooling adaptation was a ring-shaped artery arrangement in the base of the brain. This was needed because the brain burns large amounts of blood sugars, up to twenty percent of the bodyís available energy, and generates a lot of heat. The slightly cooler blood coming up from the body circulates through the loop of artery and cools the base of the brain. The paleoanthropologists who first studied this adaptation in the late pre-humans and forward, including ourselves, puzzled over its purpose2. No other higher primate has it, nor is it the simplest arrangement for conveying blood to the brain. For some of us in the present, it is even a disadvantage, as it has devolved into a structurally-weak arrangement that is prone to aneurysm.

These cooling adaptations conferred another advantage besides running endurance. Our ancestors could now move about in the noonday equatorial heat, when predators are reluctant to come out and perform any exertion, for fear of heat stroke. Even those brutally efficient runners, the hyenas, prefer to hunt in the cool of the evening.

Their last adaptation is one that we take for granted, today, but it was a critical, essential change at the time. They evolved an ability to survive for long periods almost exclusively on a meat diet. Reflect upon that for a moment. When they first came down from the trees, they had been eating a diet of fruit and tender shoots. Their physiology was not equipped to obtain benefit from meat. They couldn't digest it. But eat it they must, because their traditional food supply was disappearing. They had to forage over wide areas to obtain enough plant foods, and they had to do so in daylight, always in view of predators. No doubt, they were constantly being pursued, and they were running out of options. Top

Meat is very nutritious and energy-rich, but many physiological changes had to be made before they could exploit it. Foremost, the liver had to be modified to produce bile and a gall bladder had to be added in order to accumulate and supply the bile on demand in order to break down the fats and proteins of the meat. The linings of the intestines had to be modified to withstand the bile and absorb the new types of nutrients. The liver, pancreas, and kidneys had to have new chemical schemes in order to process the nutrients and eliminate the metabolic by-products. Moreover, these features had to be added in such a way as to not destroy the original ability to live off of plant food. [Again, if you were a genetic engineer, could you figure out how to do this?]. Today, if we switch from a mainly carbohydrate diet to a meat diet, our entire body chemistry shifts as we switch from a sugar-burning to a protein-burning metabolism.

We speak of these unique, amazing adaptations in a matter-of-fact way, glossing over the astronomical improbability of their spontaneous generation. It is as if we, today, could by mere force of will perform a sci-fi shape-shifting change of ourselves into entirely new creatures.

Our best runners, today, can run a mile in under four minutes and a marathon (twenty-six miles) in under two hours, ten minutes. It is a certainty that we could put up even better numbers in our early human days. Have you ever wondered why we have this ability? It is totally unnecessary, today. Among all of the land animals, we are among the few who can run a marathon. Moveover, this adaptation had to have occurred on the open savannas of Africa. There is exactly zero need for marathon running in forested northern locales. Remember, natural selection is parsimonious - no adaptation occurs except in response to some need. That is why some species in stable environments can exist unchanged for tens of millions of years. Clearly, in the millenia immediately before tool making and weapons use began, we had to have the speed to literally sprint with cheetahs much as they are today, and run marathons in the equatorial heat with hyenas. Top

Moreover, have you ever wondered why we, today, seem to obsessively insist upon exercising our running abilities? Are we, deep in our psyches, afraid that there will come a time when we will again need them for our very survival? Could it be that the Olympics are actually a drama replay of that time so long ago when we as a species came so close to extinction? Do we have some deep genetic memory of that terror-filled time when we achieved those 100 meter, 200 meter, 400 meter, 1500 meter, and marathon milestones one after the other? Do our Olympic hurdlers still feel that rush of primordial fear and exhilaration? Is it any accident that every world record in distance running events today is owned by a runner with East African roots?

So, assuming that our hypothesizing to this point is correct, what must have our immediately pre-human ancestors looked like? Firstly, we can state their general body conformation with some confidence, because this is the point in time that the early human fossil record begins. They were just under six feet tall, slightly built, with relatively thin bones, and standing fully upright, just like us. Their brain size was more than that of the great apes, but only about two-thirds of our own. In these facts they are unremarkable. However, if our hypothesizing is correct, they would have had a most-striking outward appearance. Due to their need for running speed, they would have been all bone, sinew, and rawhide muscle. By today's standards, they would have had a thin, wiry appearance. Their legs would be thinner, yet stronger, than those of a modern human. Today's stocky European legs are too heavy and unwieldy for high-speed running. Their feet would have thick collagen sole pads to cushion the running impacts. [We can even say with some certainty how long that it would have taken to develop specialized footpads. Consider the case of the Bolivian and Peruvian Indians who lived barefooted, at least until recently, in the cold above 10,000 feet in the Andean Mountains. They evolved thickened sole pads for insulation from the cold ground. We may quibble over the precise figure, but indigenous peoples have been in that area for less than about 11,000 years, so the adaptation had to have occurred within that time interval.] Top

But back to the appearance of our pre-human ancestors. Their muscles would not be bulky, but would be much more powerful than our own. They would be covered with a sparse, stiff fur that would help with sweat evaporation, would partially shield from the sun, would deter the larger insects, and would protect the skin when running through rough ground cover. They would have a substantial head of coarse hair, mainly to keep the sun off of the cranium and the flies off of the neck and ears. Their faces would clearly reflect their primate ancestry. They would be far more agile than any present-day human. Their body motions would be more fluid and flexible than our own. If we saw one sitting at rest, we might think, "simple primate." However, if this creature stood up and began walking, it would become clear that this was something extraordinary. The hair might stand up on our necks at the shock of recognition. If this, our own ancestor, suddenly sprinted away at even half of his/her ability, we could not fail to be awestruck.

At some time immediately preceding the development of weapons, we hypothesize that there lived an individual who was (is yet) the fastest, most powerful human or pre-human runner of all time. We base our belief on the fact that such an individual would still have had the vastly superior muscle strength of his/her recently tree-dwelling ancestors. Where we, today, take a six-foot running stride, our pre-human ancestor, with five times the leg muscle strength, might have taken a twelve-foot stride with the same or greater stride frequency. Our best sprinters can run at a speed of around 25 miles per hour (40 Kph). If our early human ancestor could double that, to 50 miles per hour (80 Kph) for short bursts, it is no coincidence that he/she could keep pace with the other common African prey animals that still use fast flight as their only defense. The Thomsonís gazelle is a prime example. It can hit 50 miles per hour in one 20-foot leap. Top

Skeptics may quibble that there is no proof that such speed was ever achieved and ask why, if we had it, did we lose it. However, the Thomsonís gazelle is proof that such speed is now and was then necessary for survival. Perhaps the best way to convince ourselves is to go to Africa and view a leopard attack and rundown of prey. Their charge is a thing of fluid, explosive power, startling in its quickness. We should ask ourselves, "Is there any way in Godís creation that we could outrun this animal?" The answer must be, unequivocally, "No!" So how is it that we are here talking about it? As for losing our posited speed, two major factors came into play. First, running at such speeds had to be extremely strenuous, demanding, dangerous, and energy intensive. Running injuries must have been common. It would be done only under greatest duress. Secondly, the advent of tool-making and weapons use began to reduce the need for running. With the pressure of natural selection gradually diminished, individuals who had less than the top running ability could now survive and reproduce.

[ASIDE: A leopard is smaller than a lion, by half, and is rather unimposing by outward comparison. However, that is deceptive. The leopard is far quicker and more agile, and has the strength to haul its own weight in prey up a vertical tree trunk. Leopards, both male and female, are solitary hunters, and do not need an accompanying group for survival. A comment by John Taylor, an African big-game hunter of the early 20th century, sums it up nicely: "If the leopard were as big as the lion it would be ten times as dangerous."]

Similarly, while we are in Africa trying to convince ourselves, we should also observe a hyena pack run down a prey animal. We will need a Jeep or Land Rover, because on foot there is no way that we could even keep in sight of this. While we are driving alongside, we should check our speedometer and ask ourselves, "Could we get out and run with them for several hours?" Top

Besides, all of the above arguments are moot. There is a modern-day, two-legged animal that lives on the African savanna and exhibits precisely the running characteristics that we have postulated for our early ancestors. Behold the ungainly-looking ostrich. Notice that it has the same eye-level perspective as do we, about six feet above ground level. Clearly, its only defense is to run. Most revealingly, it can sprint at 50 miles per hour, then can dial down to cruise and run a horse into the ground. As anyone who has ever tangled with one can attest, it has the leg strength of hydraulic machinery. It has long, thin lower legs that are covered with a tough, scaly skin, and its feet have thick pads, all of which allow it to run through rough ground cover. It did not evolve these characteristics by accident. They are precisely what it needs for survival, and no more. It is presently coping with the exact same predatory threats as were faced by our late pre-human ancestors. There is no reason to believe that we somehow had the luxury of doing any less.

No doubt, our pre-human ancestors observed hyenas harrying and running down prey (and were subjected to it, themselves!) and said to themselves, "We can do that." This is all the more plausible because somewhere in that pre-weapons period, our ancestors began eating meat. Up into the mid-twentieth century, the Bushmen of the Kalahari desert used this hunting technique. Carrying nothing but water in animal-skin pouches and a spear, a Bushman would pick out an adult antelope and begin tracking and harrying it in the heat of the day. They would keep this up for as much as eight hours, until the animal collapsed of thirst and heat exhaustion. It is stunning to realize that this practice might be more than a million years old. Top

While we are on the subject of the first weapons, of course there were hand axes and spears, but there was another that is often overlooked or downplayed: The early humans, who were the size of a large modern human, quite likely had a powerful, deadly-accurate, throwing arm. Recall that these creatures had substantially the same arm strength of a tree-dwelling primate; i.e., between five and ten times that of a modern human. With this strength, they could throw harder and with greater control. Consider that a big-league pitcher can throw a five-ounce (142 gm) baseball at nearly 100 miles per hour (160 kph), and if he hits a batter in the head, it can be fatal. Now consider that an early human could throw substantially faster and with a heavier object. It is not out of the question that he could double modern-day speeds, to near 200 miles per hour (320 kph), but let us speculate that he could throw a half-pound (eight-ounce; 227 gm) rock at "only" 150 miles per hour (240 kph). A lion, for example, would not have time to react to such a missile, and if struck in the head the lion would drop straight down, dead, without a further twitch. In fact, in modern times large animals are slaughtered by similar sharp blows to the head. Felis leo would have quickly learned to avoid such danger. Top

[For you baseball fans out there: Imagine yourself as a catcher faced with a pitcher so powerful that he can throw a curve with a smooth, half-pound rock. His first pitch starts out high, dead between your eyes. You are so startled at its speed that you freeze. At the last instant, it breaks sharply to your left. Fsst! You hear the sizzle. The rock shatters to pieces against the concrete backdrop. His next pitch is again high, but a little to your right. You know what is coming, but you do not have time to even begin raising your catcher's mitt. It breaks sharply and BAM! hits you in the forehead. Your skull is cracked open like an egg. Sayonara!] Top

It is a fact that modern-day baboons and chimpanzees occasionally throw rocks at their attackers, but they do not have sufficiently advanced brains that would allow the fine control and purpose that we have postulated, above. There are even faint echoes of a throwing instinct in modern-day youths. Young boys, just as do the young of any higher mammalian predator, prepare themselves for their ancient role. Those who live in the country and who spend a great deal of time outdoors without supervision, from the youngest ages, will play-fight for dominance, footrace each other, climb anything and everything, memorize every square inch of their territory - and throw rocks. Lots. Often. At first, they throw at random, but as they grow they begin to zero in on specific targets, and they can become quite accurate. Competent throwing is among their first acquired skills.

Who Were They?

By freely hypothesizing among the known facts, we have constructed a scenario, a sequence of events, by which tree-dwelling primates evolved into humans. Working from only the environmental changes and the known predatory conditions, we have proposed three phases of our evolution: (1) A tree dweller who was forced to spend time on the ground foraging; (2) A primarily ground dweller who was forced by predation to become a competent sprinter out to 400 yards, but who had some recourse to scattered trees; (3) A fully ground-dwelling type who was almost hunted to extinction by predation, narrowly avoiding it by developing marathon running skills and, eventually, weapons. Top

So, while we are at the business of hypothesizing, let us go to the fossil record and put names to our cast of characters. The first type, a primarily tree dweller, was Australopithecus Africanus. This individual was bipedal, but had the relatively short legs of a small ape and the feet of a tree dweller. It must have had a slightly stooped posture, much like a chimpanzee. It would have spent most of its time in the trees, coming down only to forage. This creature flourished for around three million years. Toward the end, it had begun to use simple stone tools, probably because its only remaining, reliable source of food was roots and tubers that had to be dug from the ground and have some rudimentary preparation for eating. We speculate that during the span of A. Africanus' existence (5-2 million years BCE), the local environment went from subtropical forestation to arid, treeless grasslands. Without the sanctuary of the trees, A. Africanus as a pure type was hunted out of existence. Its legs were too short for outpacing the big cats. Top

As A. Africanus was fading, our second figure in the cast appeared. His name is Homo habilis, meaning "handy man," after the numerous tools that he employed. He was almost certainly a superior strain that developed out of A. Africanus, his most notable advances being longer legs, a larger brain, and a more upright posture. It is he who first "stood fully upright and gazed out over broad grasslands." It is he who first developed the sprinting skills to escape a leopard's charge, made possible by his longer legs. It is he who first began eating meat, probably from scavenging, but also as a side benefit of digging for roots and tubers. No doubt, many small burrowing rodents would have been encountered. Imagine if he came upon a burrow packed with African mole rats-they would have been consumed whole, on the spot, and H. habilis would have quickly learned how to find more. The reign of H. habilis was short, between 2 and 1.5 million years BCE, because this is the time interval in which we have hypothesized that the hyena and wild dog developed their very effective pack hunting behaviors. H. habilis was a good sprinter, but no match for the pack hunters with their harrying, relentless, marathon pursuit. This part of our hypothesis should be verifiable via the fossil record. If true, then the numbers of pack hunter fossils should have significantly increased in this time period. Top

As H. habilis in turn was inexorably hunted out of existence, our third cast figure appeared. His name is Homo erectus, meaning "fully erect man." As above, he was almost certainly a superior strain that developed out of his predecessor, H. habilis, his most notable advances being still longer legs, an even larger brain, the ability to sweat, the development of weapons, and active hunting of other large creatures, probably other primates and even H. habilis, his ancestor. Up to six feet tall, he was recognizably human. Not at first having weapons, it is he who became the Penultimate Runner, and he who learned to hurdle through thornbush in order to stymie his pursuers. Eventually, this clever fellow developed spears and axes for hunting and defense. After the first time that he backed down a lion with a spear and a well-aimed rock between the eyes, the world would never again be the same. The lions, leopards, and pack hunters of Africa couldn't know it, of course, but they just had unleashed the terror of the natural world. Top

Emergence of Intelligence

There is one last twist to this tale, and it is a doozy. If Harris is right about our developing larger brains for redundancy and ultimately running endurance and agility, and if Hawkins is right about the basic neural organization of the brain, then intelligence did not develop primarily as a survival tool, but as an unexpected consequence! Every neuron that was added for running endurance was also another neuron that could participate in rational thought. Just at the point where we were about to be overwhelmed in the escalating war over running speed and endurance, we suddenly whirled about and faced them off with weapons! Here is a case that might be viewed as not just a natural mutation, but as the mother of all natural mutations, inasmuch as literally nothing in the world would be safe from its grasp, not even the ground upon which they stood. Now they had tools, and soon, fire. The Old Testament [Genesis 11:5-7] might well have been addressing this small handful of the first humans when it observed "... this they begin to do; and now nothing will be restrained from them, which they have imagined to do." [emphasis mine] Top


Some five million years ago, a small, fragile creature climbed down from the trees and, against all odds, lived on the African plain among numerous and frightful predators. This creature walked upright, in daylight, in full view of predators. What we have postulated above might not be an accurate account of how this creature survived and became human; but if not, then even more bizarre scenarios must be considered.

I would have liked to have been there when the first leopard stalked up on a small band of early humans and found that not only did they not run, but they were in an ugly mood - and armed with spears.


1. Chris Stringer and Peter Andrews, The Complete World of Human Evolution, Thames and Hudson, London, 2005.

2. Marvin Harris, Our Kind, Harper & Row, New York, 1989.

3. Jeff Hawkins, On Intelligence, Henry Holt & Company, New York, 2004. Top


This author composed the present speculative essay largely without reviewing the most recent scientific literature. Recently, I was privileged to read the eye-opening paper, "Endurance Running and the Evolution of Homo," Nature 432, 345-352 (2004). Beautiful.

There is yet another running adaptation that hasn't been mentioned, as follows. In recent years, marathoners have noticed that East African runners, who own most of the distance records, use a different style of running. They keep more flex in the knees and appear as if they are trying for minimum impact when they put a foot down, as if running on eggshells. The question is, how did they arrive at this style? I submit that it is because they, and all our far-distant ancestors, learned to run barefooted. Speaking as one who did a lot of barefooted running as a young boy, this author can say with authority that one will not for long pound along stiff-legged, on bare heels. Sharp stones and thorns will see to that. Instead, with flexed knees, if one puts down a foot and senses something sharp, one can reflexively collapse the knee and pick up the weight with the trailing foot on the next stride. It might also be a mere fortuitous side effect that this running style requires less energy, thus aids endurance running.

Humans also have the evolutionary reflex to collapse the ankle to the side to avoid a puncture of the foot or excessive stress on the joint. These reflexes did not suddenly appear. My guess is that they go far back, probably to the time of H. Erectus.

© 2005, 2006
Clyde M. Davenport
Updated 7/19/06, 2/21/10

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