For more than 50 million years, the canopy environment has placed stringent evolutionary conditions upon existence within its domain. Primates are a result of that process. Some examples of primate adaptations traditionally attributed to evolution within the canopy include binocular and color vision, long arms and legs, fingernails, grasping thumb, broad shoulders, enlarged brain, vertical posture, giving birth to one young, and a head that sits at a right angle to the spine. Certain features once thought to have originated in the terrestrial environment have now been added to this, including bipedalism among large-bodied apes and a long, opposable thumb. Over the last decade and a half, fossil discoveries have continued to strengthen the view of the canopy as a source of protohuman adaptations.
Since the time of Darwin, theories of human evolution have taught that the arrival of bipedalism brought an end to our dependence on trees. That event cut us loose from our boorish primate origins, freeing us to fulfill our destiny. Arrival at the ground was a fundamental turning point in our lineage that set our hands free to work miracles, and with that, we never once looked back at our arboreal birthplace. Yet since the discovery of Australopithecus afarensis, there has been a growing list of potential ancestors that have turned this view upside down. Not only were they active bipeds, they were also active climbers. These climbers are prominent names in our ancestry, such as A. africanus, Homo habilis, and H. rudolfensis, to name a few. Naturally, the ancestors of those early bipeds were also thought to have been climbers. As shown below, even H. erectus, who is viewed as exclusively terrestrial, used tools designed for canopy applications.
Oddly, the knowledge that our early bipedal ancestors spent considerable time in the canopy has not percolated down into theories about the evolution of human nature and the brain. The original theories, formulated from strained academic efforts to hide our affinities with apes over the past 150 years, promote an outdated terrestrial view of evolution that remains largely accepted and intact. “Canopy theory” unifies myriad disparate data into a single, cohesive, commonsense framework. Comparing terrestrial mammalian evolution during the Cenozoic with primate and marine mammal evolution raises doubts that the terrestrial environment could have been a habitat that promoted encephalization. Canopy theory encompasses early primate evolution and shows that the arboreal process of primate encephalization did not cease once our ancestors arrived at the ground. On the contrary, it shows that a reinvigorated arboreal encephalization process ultimately led to the human-sized brain. To demonstrate the strength of the canopy viewpoint within the space permitted, several of the more intractable problems that, as yet, lack satisfactory explanation will be discussed. These include the loss of thick body hair, tree platforms, and early weapons, such as the Acheulean hand axe.
Naked Ape in the Canopy
Primates are most noted in being quadrumanous, having four hands that are essential appendages for safe travel in the canopy. Quadrumanous primate young cling to the mother’s body until they are capable of independent travel. A few million years ago, evolution sidestepped when the hands at the end of our legs began to evolve into feet. From the canopy point of view, nothing could be more radical. Becoming bimanous greatly altered the behavior of our ancestors in their treetop habitat and led directly to changes in our morphology. This impacted reproductive behavior and drastically undercut the proven primate suite of coevolved adaptations between mother and young that determined how infants were transported from place to place.
Transforming a hand into a foot was a major engineering modification. Long fingers were converted into short stumps called toes, and what was an opposable thumb was realigned to become a nongripping big toe. This made the infants’ toes useless for hanging onto the ancestral primate mother’s gripping-fur. The infant had lost a pair of gripping hands, reducing its attachment points to the mother’s body by 50%. This was a revolutionary mechanical shift in load that resulted in extremely high selective pressure. Gripping-fur and infant hands were a tight revolutionary duo. Change in one immediately forced a complementary change in the other.
An example of coevolution can be seen between trumpet blossoms and hummingbirds. Some trumpet flowers gain reproductive advantage by limiting access to their nectar. This can occur simply by elongation of the floral tube. Over evolutionary time, hummingbird species responded with longer bills to match the changing depth of floral tubes. Close coevolutionary relationships like this have enriched the diversity of the planet’s life by promoting new species.
The ancestral bimanous infant had a less secure grip on its mother’s body. The traditional view explains that the bipedal mother accommodated this change by simply retaining her gripping-fur and holding the baby with her arms, while her hips broadened into a sort of saddle on which to carry her young. But the fossil record tells us that broad hips did not arrive until the infant developed a larger cranial size, a more recent adaptation. Therefore, large hips could not have played a role in the adaptations needed to support the bimanous ape infant. In addition, the fossil record indicates that we still climbed trees when we were bimanous bipeds, and it can be reasonably inferred that hand carrying an infant while climbing would not have been possible. More than ever, we needed our two remaining hands to climb; there were no spare hands to help an infant.
So, how were the young carried? Did they hang with full body weight from two fistfuls of gripping-fur as the mother clambered amongst limbs? From a purely mechanical point of view, climbing is a tortuous activity that can require swings, rapid turns, accelerations, decelerations, and other acrobatic feats. For an infant trying to cling to its mother, the loss of two attachment points would have resulted in a major and deadly mechanical instability. At times, a bimanous infant would pendulum, shifting full body weight from hand to hand. This would produce forces well over a 100% greater than those endured by the infant quadrumanous ancestor. Either the gripping-fur would have pulled out or the infant would have lost its grip. Hanging from two hands or being supported in the mother’s arms would have led to extinction.
One coevolutionary solution to the reduction in attachment points would have been to increase the holding power of the infant’s remaining two hands. Babies today do seem to have an unusually strong grip reflex. The increased strength of the infant handhold would have been matched by an increase in the strength and length of gripping-fur on the mother’s body. This would help ease the tension that developed between the coevolved hand/gripping-fur pair. And this is exactly what happened. Of all apes, we have the thickest, strongest, and longest hair, but that gripping-fur does not cover our bodies. It is found only on the head.
So, why do we have long, strong gripping-hair only on our heads? Because the bimanous grip on body hair was still risky. Safety (natural selection) required that long, strong, gripping-hair be located adjacent to a stout support position for the lower part of the infant’s body that no longer had gripping hands. There is but one location on the human body where that evolutionary formula fits: the shoulders. If this sounds awkward, remember that infant size was smaller, and the infant might have been more precocious than today. Perhaps this is why children love to be carried in that fashion. Humans have longer necks than apes, suggesting the ancestral neck may have lengthened around the time feet lost their ability to grip.
With hands clutching the mother’s gripping-hair and legs securely around the neck, the infant’s weight rested in the only mechanically safe position available. Long head hair, a long neck, and lack of gripping-fur on the body are the results of a coevolutionary process associated with successful reproduction. We are the only “naked ape” specifically because we are the sole extant bimanous ape. Other explanations that have been advanced for the loss of hair, such as thermoregulation, parasites, swimming, and sexual selection, may have acted to reenforce the coevolutionary changes between mother and infant, but not necessarily.
Grip-Climbing in the Canopy
The structure and function of the feet of all mammals require or allow certain forms of behavior and preclude others. The bimanous ancestor that led to humanity would have climbed differently from a quadrumanous ape and would have used the spaces within a tree differently. The shorter fingers, expanded apical tufts, and longer thumb of the bimanous biped are adaptations for grip-climbing: not for toolmaking, as has always been claimed, and not for suspensory climbing. Grip-climbing requires holding onto large-diameter limbs and trunks that have bark grooves; it employs the thumb to a greater degree. The bimanous ancestor was specialized for climbing within tree crowns among the larger branches where weight is borne on the foot while standing in a vertical position.
Conversely, the quadrumanous ape’s long fingers and a shorter thumb are well designed for suspension from branches, providing much safer access to the distal portion of limbs. Sometimes, fossils that have humanlike features are compared to chimpanzee skeletons to try to decide whether or not the fossil ancestor was arboreal. But since the bimanous hand evolved for grip-climbing and for access to the internal tree crown, rather than for suspensory climbing, one cannot directly compare a bimanous skeleton to a chimpanzee and come away with a reliable estimate of the time a bimanous ape spent in trees.
Neocanopy
All great apes build nests, including humans, so there is little doubt that our bipedal ancestors would have built nests much like those made by apes. Recent views on the origin of human nature accept that our bipedal ancestors would have spent time sleeping in the canopy, and there is some acceptance that sleeping-tree locations may have contributed to various aspects of the fossil record. However, these meager acknowledgments fall short of explaining what must have been taking place in the canopy.
H. sapiens, the only living bimanous apes, build tree platforms of a much different style than apes. This style is another facet of the transformation that occurred when our four-handed, bipedal ancestor lost the ability to grip with its feet and became a bimanous biped with an enlarged brain. This places the origin of improved “tree nests” during the time of H. habilis.
Becoming bimanous reduced safety, which would have been compensated for by building a stronger nest in a safer location. Safety translated into larger diameter limbs and stronger “nest” materials. Bimanous ancestors would have used trees with a shape and form that supported larger and stronger tree platforms. Ideal tree limbs were situated over water, where a soft landing was possible after a fall. Optimal tree locations inhibited predation by large cats and allowed simple aerial hunting. Stronger nests took more time to make, leading to reuse of nests. At some point, the bimanous tree nest became a tree platform.
Tree platforms were designed for the terrestrial foot. In subtle ways, the redesign of the quadrumanous nest into one that was bimanous created a totally new environment. That environment would have been unlike any canopy refuge of the past as it evolved into a kind of aerial home base. Canopy theory calls this neocanopy habitat the terrarboreal habitat.
Theorists have long sought an evolutionary feedback process that would promote ongoing brain evolution. The origin of the terrarboreal habitat offers a new explanation for the expansion of the brain of Homo habilis, about which little is understood. Canopy theory proposes that the terrarboreal habitat, along with associated inventions that improved safety and access to the canopy, was the principal force behind the evolution of the human mind. Specific activities that took place in the terrarboreal habitat led to humanlike social interactions, the earliest use of language in the command form, the development of weapons for defense and hunting, early aerial hut designs, and inventions such as roofs, knots, rope, and many others.
The archeological record is practically devoid of terrestrial home base and sleeping sites used by early and later bimana. Tree platforms would have provided dependable security from terrestrial predators, whose strength and competitiveness have been routinely underestimated. Our ancestors spent most of their sleeping hours on canopy platforms. When boughs broke or trees fell, platforms crashed to the ground and were demolished, not likely to be exposed by the trowels of future scientists. Canopy theory speculates that our ancestors routinely used tree platforms until some time after around 50,000 years ago. Our move to a full-time terrestrial existence would have to remain tentative until we could protect ourselves against carnivorous competitors. Once that was achieved, we bade farewell to our birthplace in the trees and began a far different and in some ways more challenging and dangerous journey at the ground.
But such inferences bring us to a theoretical landscape, an uncharted “arboreal continent,” that has never been explored by human evolution theory. There are numerous partially written stories and vignettes locked in the attic of human origins waiting to be brought down and dusted off. One well-kept secret is that strength alone can turn a human into an active climber. H. erectus had basically the same body design as humans, but with a distinct arboreal advantage. Researchers describe the H. erectus arm and shoulder girdle as apelike and robust, meaning exceptionally strong. The upper arm and grip strength of H. erectus would have made the species better climbers than strong humans. Robust is a frequently used word in terrestrial theories. It is another secret that had been locked in the attic. Whenever a primate skeleton is robust and its body is human size and smaller, it is always, without exception, associated with arboreal activities. Although H. erectus is viewed as a terrestrial primate species, its body form tells us it climbed into the canopy. What was it doing there?
Hand Axe: A Canopy Tool
The hand axe is considered the calling card of the African H. erectus, but its exact use is still being debated. These axes are found from South Africa to Europe in the west and India in the east. Hand axes come in many different sizes, with a general trend toward reduction in size over time. The earliest Acheulean hand axes are dated at about 1.5 million years old and were found at Peninj, in West Natron, Tanzania, Africa. This section concentrates initially on early hand axes that have a general tear-drop shape, are about 10 inches long, and weigh about 5 pounds. Issues that remain unresolved are: Why was such a large, hand-held tool bifacial? Why are they found in dense accumulations associated with ancient water? And why did the design remain basically unchanged for over a million years? All are answered by a single canopy explanation.
Hand axes resemble large spear points, but some weigh up to 50 pounds. This huge difference in size has given rise to several views on the tool’s use. There is no chance that the largest hand axes were thrown or used as spear points. Some researchers believe large hand axes represent early religious symbols, perhaps worshipped by a kind of Stone Age, hand axe cult. Even the 10-inch-long varieties could not have been hafted as a terrestrial spear, as the butt end would have been too thick. Some say these tools were large carving-and-skinning knives, and still others feel they were thrown at prey. However, neither underhand nor overhand throws would produce the velocity needed to make the hand axe a weapon.
A discuslike throw could produce the necessary velocity to debilitate prey, were it not for a glaring limitation of H. erectus. The vertebrae of the Turkana Boy, an H. erectus approximately 11 years old, show that the spinal cord opening of his species was considerably smaller than ours. Since the opening is for motor and sensory neurons, it has been concluded the species could not have had great coordination. It would have been impossible for H. erectus to perform the precise spinning motion needed to hurl a hand axe like a discus, even if such a throw could be aimed effectively. This limitation would apply to any hunting technique that requires highly coordinated activities.
Like empty gun-shell casings, hand axe sites are forensic evidence of their principal targets and form of use. Hand axes are typically found in unexpectedly high densities and in clumped distributions. Some locations have thousands of these artifacts piled on top of one another, while others have tens of thousands. If hand axes were used as hand-thrown terrestrial spears and throwing rocks, we would expect to see them more widely distributed, coinciding with animal distributions. But they aren’t. They are in large piles where they fell after they were used. The key to their use is the one-on-top-of-another accumulations.
Hand axes typically are found near ancient riparian habitats where large trees were likely to have grown. The hand axe was actually a “drop-chisel.” It was dropped from high arboreal positions onto prey.
Counterintuitively, the working end of the hand axe was not the pointed end; it was the chisel-shaped, blunt end. Kinetic energy of the falling hand axe was focused on a chisel edge, giving H. erectus a simple-yet-powerful hunting strategy that required little physical coordination. From lofty perches over ideal hunting grounds—watering holes, fishing pools, and river crossings—a vigilant eye kept watch over a diversity of creatures that congregated below. Hunting that took place in the same location, day after day, year after year, over hundreds if not thousands of years, would have been simpler from the comfort of a tree platform.
What about that meter-long, 22-kilogram hand axe? Was it really the first religious idol, or was it something far more practical? Carrying a heavy rock into the treetops could have been accomplished by a robust bimana, but holding the stone over a target while balancing on a limb would have been difficult. Use of this unwieldy tool would have required a tree platform. No longer can it be claimed bimana lacked an effective killing weapon.
Drop-Tools
The drop-chisel did not appear out of thin air; it had a predecessor. Drop-chisels evolved from “drop-rocks” associated with H. habilis and more ancient ancestors. These rocks would have been collected from riverbeds and talus slopes. Their use stemmed from the common primate habit of bombarding potential terrestrial threats with falling objects. Recognizing that drop-rocks would stun or kill small mammals and surface-feeding aquatic vertebrates, such as turtles and fish, would have been a natural outgrowth of typical primate behavior. Masses of irregular rocks, spheroid and choppers, have been found in the geologic strata known as Bed I at Olduvai Gorge. The present view of these accumulations is that they are stone caches; however, some appear to be deposited within light sediments and in aquatic settings. This indicates these “caches” were actually drop-rocks that settled to the bottom of a mud hole and/or accidentally fell off a tree platform and were lost.
Over time, an understanding of the merits of a tear-drop or fusiform rock over a round drop-rock would have dawned on our ancestors. A fusiform rock penetrates into water and therefore would have been a better fishing tool. As a hunting tool, a fusiform rock cuts through skin, as opposed to a round rock that bounces off. This naturally occurring shape can be found in both talus slopes and fractured shale deposits, and superficial adjustments wouldn’t have required great intellectual prowess.
A natural, tear drop-shaped stone was used to test the manner in which the original drop-chisels were held. This stone was dropped from a height of 13 meters, a distance from which one can reliably strike a soup can. Practice is needed to guarantee a drop-chisel will strike edge first. How the drop-chisel is held is critical. Any rotation whatsoever imparted to the tool when it begins to fall tends to turn the leading edge parallel to the earth before it strikes the ground. Prey struck in that position might be stunned, but perhaps not killed. Think of a hand axe as a pendulum. It must be held by the pointed tip, and no matter how still it is held, it will swing a little at the chisel end. A thinner trailing end is easier to hold and more likely to fall true. A bifacial edge on the hand axe could have resulted from paring down the trailing end to provide a steadier grip. With sharp edges, even a near miss could result in a deep gash that would be at least debilitating. Continued tapering of the pointed end would produce a more stable drop-chisel shape known as an “Auchealean pick.”
Onetime use of some drop-chisels accounts for why they are often found in nearly perfect condition. It is unlikely that drop-chisels were ever discarded intentionally. They were retrieved from water and mud until lost, or at times, they may have been abandoned due to the ill intent of predators lurking below the surface.
Investigators report wood deposits on the Pininj drop-chisels, suggesting they may have been used to cut down straight saplings or branches for shafts. The drop-chisel’s sharp-pointed end was a self-hafting blade. Driving the blade into a shaft of green wood would split the wood, creating a pinching force that held the blade in place. The thick end remained the killing end. A wooden shaft combined with the stone would have weighed about 10 pounds. This increased weight improved killing power, and a long shaft fell straight and simplified hunting. The drop-spear was a huge step in drop-tool evolution, as it permitted the use of more recent, flatter hand axes and other shapes that were sharpened around the perimeter. Unwieldy as a terrestrial spear, the drop-spear was an ideal canopy weapon. Thrown at an angle rather than a straight-down trajectory, the drop-spear became the first step in developing a terrestrial spear with a stone point.
Canopy Hunting Platforms
Hunting platforms probably originated during the early Stone Age. A huge effort has gone into trying to divine an answer as to whether or not our bimanous ancestors were hunters or scavengers. It is presently believed these early ancestors were scavengers based on the frequency of tooth marks found on fossil bones. But this determination has not taken canopy-hunting activities into account.
Early bimana would have discovered that leftovers tossed from tree platforms attracted animals. We also know that bimana accumulated stones from the countryside for use as tools. This brought them in contact with kill sites, where they collected long bones previously gnawed by carnivores and scavengers. Back on the tree platform, the bones were crushed, and the marrow was eaten. The remains were then dropped off the platform where they lay strewn below on a stream bank or possibly in the water. There, the leftovers would act as bait, attracting both terrestrial and aquatic vertebrates. After killing one of these scavengers, large chunks of meat were slashed off. Most writing about the subject assumes without question that during such butchery, the stone knives would have scratched the bone. This would not be true if the amount of food made available was in excess of the needs of the hunter. In that case, butchery would have taken place without scratching the bone, while leaving behind plenty of meat for scavengers to consume. Canopy hunting would likely guarantee kills in excess of needs. Below a hunting platform, one would expect to find bones that had been gnawed upon by predators, with few cut marks, as well as cracked and splintered shards of crushed long bones. Obviously, cut marks and tooth scrapes on bones do not tell us much about the activities of our ancestors, whereas bone assemblages, stone piles, drop-chisel design and accumulations, and the robust morphology of our ancestors point to a single conclusion: Our bimanous ancestors were effective canopy hunters.
Turning to some of the sites at Olduvai Gorge, site FXJj50 at Koobi Fora has characteristics that indicate it was a refuse pile from an ancient hunting platform where bait may have been used to attract prey. Bones may have been brought to the site that were already gnawed by carnivores. One of the more interesting bone accumulations studied by Mary Leakey was the FLK- Zinj excavation in Olduvai Gorge. The bones in a portion of those accumulations had an arc-shaped assemblage, once interpreted as a windbreak. The “canopy view” is that the arc-shaped area may have resulted from the fallout shadow of an arboreal home base. Long bones of ungulates are the most frequently found bones in the pile, and it is thought that these were brought to the location from elsewhere. These could have been killed at platforms near watering holes, then brought back to the living platform in the canopy. At another Olduvai site, the percentage of carnivore remains in the bone assemblage reached 21%. This is an extremely high figure that is very unusual. This indicates carnivores were being attracted to bait under a tree platform, then killed as prey.
King of the Jungle
The present terrestrial view of our ancestors is that they were poor at protecting themselves, which was probably true out on the savanna. But an arboreal, bimanous biped who was capable of transporting heavy rocks would have been a formidable forest species. From a lookout in the canopy, movements of dangerous animals below could be observed vigilantly. Predators within the forest were driven off and/or injured. Our ancestors, not large cats, dominated select regions of closed and riparian forests.
The evolution of drop-chisels and drop-spears strengthened our ancestor’s control over forested areas. This long-term control is demonstrated by fossil discoveries at Olorgesailie, Kenya. Artifacts there span hundreds of thousands of years and led to the discovery that hand axes did not change in shape over an extended period of time. One of the more intriguing bone accumulations at Olorgesailie included more than 60 giant-baboon skeletons intermingled with lost drop-chisels. A variety of scenarios have been suggested, but the logical explanation is that these formidable animals were slaughtered through stealth from above. Drop-spears were probably the weapons of choice. Olorgesailie is a classic canopy-hunting site. Data on changing biota and climate establish that over a long period of time, canopy hunting was a reliable way to obtain food. The long life of the drop-chisel establishes that its design was an invention like the wheel. When a tool fits its function, the function defines its form.
Neocanopy Brain Evolution
From the end of the Cretaceous period, the canopy environment stood apart from the ground as a habitat that could promote brain evolution. Primates evolved within that aerial habitat, where they developed a brain-to-body-weight ratio greater than all terrestrial mammals. This ratio changed little over tens of millions of years. During the proliferation of Miocene apes around 15 to 20 million years ago, many species of apes developed larger brains as a result of attaining a larger body size, but they still possessed a brain-to-body ratio little different from that of monkeys. At that point, brain expansion reached a plateau where chimpanzee brain size remains today, but in our lineage, a new spurt began about 3 million years ago. Encephalization in the canopy recommenced as our ancestors were becoming bimanous. The terrestrial habitat played only an indirect role limited to the transformation of a pair of grasping feet into nongrasping feet.
The physical adaptation process produced grip-climbing and modified the hand into its humanlike form. This precipitated simultaneous mental and behavioral adaptations. All of these were associated with the origin of terrarboreal platforms. Two or more individuals were needed to build the larger terrarboreal platforms. The terrarboreal habitat included platforms, roofs, walls, and probably, as with bonobos, more than a single family might have built within a single tree. When one individual was on the ground and another on the platform, the distance between them encouraged verbal and visual communication that led to rudimentary sign language and the first commands of a spoken language. Practical inventions of the terrarboreal habitat could have included rope, twine, knots, bags, and several types of drop-weapons. This author is confident that terrarboreal habitats and inventions needed to keep bimanous apes safe while living in the canopy will prove to be the single most important suite of mental changes and adaptations that acted together synergistically for the evolution of the human mind.
Traditionally, encephalization is attributed to activities taking place on the ground as a result of bipedalism. However, there are no biological examples that demonstrate that the terrestrial habitat can produce primatelike encephalization. On the contrary, when primatelike encephalization has occurred, it was a result of a “multiple-habitat effect,” a process described by canopy theory. The parochial, paleoanthropological view that a terrestrial habitat promoted human brain encephalization lacks rudimentary biological support. No biological doubt exists about the canopy’s ability to promote encephalization. Given the existence of the terrarboreal habitat, we have arrived at the most compelling biological explanation to date for the growth of the brain: that growth was a neo-canopy phenomenon that took place above ground in the evolving terrarboreal habitat.
Our ancestors did not walk along a dusty path on their journey to become human; they traveled arboreal highways of a lost, treetop world. Signposts from our passage through a canopy world can still be seen in ancient Greek columns, cathedral design, skyscrapers, hunting platforms, tree houses, children’s playgrounds, and the innate reflexes of infants. These represent vestigial sentiments and behaviors that sustained us during millions of years of intimate treetop evolution. The interwoven boughs of majestic forest trees, like mother and infant to be, were the nurturing womb of the human mind.
References:
- Clarke, R. J. (1999). Discovery of complete arm and hand of the 3.3 million year old Australopithecus skeleton from Sterkfontein. South African Journal of Science, 95(11/12), 477-480.
- Dawkins, R. (2004). The ancestor’s tale. New York: Houghton Mifflin.
- Dominguez-Rodrigo, M., et al. (2001). Woodworking activities by early humans: A plant residue analysis on Acheulian stone tools from Peninj (Tanzania). Journal of Human Evolution, 40, 289-299.
- Isaac, G. (1977). Olorgesailie: Archaeological studies of a Middle Pleistocene lake basin in Kenya. Chicago: University of Chicago Press.
- Klein, R. G., & Blake, E. (2002). The dawn of human culture. New York: Wiley.
- Perry, D. R. (1986). Life above the jungle floor. New York: Simon & Schuster.
- Tattersall, I. (1995). The fossil trail. Oxford: Oxford University Press.
- Walker, A., & Shipman, P. (1996). The wisdom of the bones. London: Weidenfeld & Nicholson.
