This is Part 5 of a subscriber-only preview of my upcoming book Outsourcing Consciousness: How Social Networks are Making Us Lose Our Minds. We will release the first six chapters through the end of the year. Read Part 1, Part 2, Part 3, and Part 4.
O wonder!
How many goodly creatures are there here!
How beauteous mankind is! O brave new world,
That has such people in't!
Miranda, from Tempest, Act V, Scene I by William Shakespeare
If the arguments for the adaptive benefits of structured language and story are practically self-evident, the opposite might be said for bipedalism. It is not at all obvious that the mutations necessary to become bipedal represented sensible adaptations to the world of the African forest-savannah mosaic at the threshold of the Late Miocene and Early Pliocene between 4-8 million years ago.
That is not because anatomically modern human bipedalism doesn’t yield clear benefits – it does! Yet one of the pitfalls of evaluating the evolutionary advantage of an adaptation is that we are prone to imagining its benefits in an advanced state of evolution. We presume by default the selection of various subsequent helpful and related mutations that accompanied it, and those which took place downstream of those mutations. When we consider something so grand as what it took to get us walking on our own two feet, the list of what we might have in our minds could grow very long indeed. Surely, we must consider the way in which the pelvis evolved to a platypelloid structure with flaring ilia[i], the redistribution of lower limb muscles, the reduction in muscle mass to body weight, the metabolic need for higher body fat percentages, lower skin mass to accommodate heat regulation during bipedal movement, and significant adjustments to balance and posture control to accommodate a brain that underwent a three-fold increase in size[ii]. And obviously we will take into account the modification of the ankle to a globular shape to support bipedal loading patterns[iii]. It would be a crime not to assume we’re dealing with all the adaptations to the heel bone necessary for bipedal locomotion as humans practice it[iv], naturally, and if we’re doing that we might as well consider a broader range of changes in proportions, especially those which made our skeletal structure somewhat independent of body width to maintain an optimal gait[v]. All of that, of course, almost presupposes that we are assuming subsequent modifications to the shape and size of the birth canal, the width of the natural form of the body, and other pelvic adaptations relating to heat regulation[vi].
The point, of course, is that these adaptations and the benefits they offer emerged over hundreds of thousands, and in many cases millions of years. In between were trial mutations which may or may not have been helpful at all. At the very first stages of evolution downstream of Caliban, as I interjected last chapter, it would not be very wrong to think of us as glorified chimpanzees with a janky hip mutation. The whole notion that we can simply tick off a list of the many benefits of a system of related adaptations in isolation from the uneven process whereby they were acquired is ludicrous. Yes, as we will explore, bipedalism led to much of what made us human. It yielded benefits which permitted humanity to become the dominant species on our planet. And yet, at the very first, its evolutionary advantages were marginal at best. At least on the surface.
When Orrorin walked the earth there is no evidence that Caliban’s sons and daughters were proficient toolmakers to any degree that exceeded the capabilities of modern chimpanzees and bonobos. The first such evidence we have found was from millions of years in the future. Hominins taking their first bipedal steps were already reasonably proficient in the motor skills necessary for gesturing, but there is precious little evidence or reason to believe that these first steps would have produced immediate incremental results in communication. The difference in the gesture and pantomime possible for an obligate bipedal animal and one capable of selective and context-dependent bipedalism were not so different that it would seem an adequate cause for a massive and multidimensional change in physiology. Likewise, while it is possibly true that even the first mutations on the path to bipedalism might have permitted us to be a glorified chimpanzee with a janky hip and a related ability to reach higher for fruit or see a predator from further off, it is hard to imagine that this alone would justify such a costly change in our physiology.
And that is precisely what bipedalism is. It is a costly adaptation in multiple ways, and obviously beneficial in only a few, at least at first. Walking bipedally in the way humans do can be significantly more energy efficient than chimpanzee brachiation or quadrupedal locomotion, especially over very long distances[vii]. This benefit relies, however, on morphological adaptations that may not have been present in Caliban and his immediate descendants. Any net energy benefit in the early stages of evolution in this trait may have been smaller[viii]. Maybe even negative[ix]. Beyond energy expenditure considerations, bipedalism also subjects the body to a new set of injury risks, placing new strains on the lower back, hips, knees, and ankles. The spine, pelvis, and lower limbs must support the entire body weight[x]. Bipedal creatures require much more demanding apparatuses for balance, and even with those capacities are subject to tipping and falling at greater rates than with other means of locomotion[xi]. Over the short distances predators and prey generally would have pursued or been pursued by our hominin ancestors, both quadrupedal movement and brachiation would probably have been more useful[xii]. The adaptations required to facilitate bipedalism are sufficiently specialized that they create a stronger obligation toward that means of locomotion. There is a reason the last time you did bear crawls was probably during junior high school field day. Or during Crossfit. But if you were into Crossfit, you'd be doing Crossfit, not reading this book.
The costs of the early stages of bipedalism were not confined to inefficiency. While transitional bipedalism almost certainly emerged both in the trees and on the ground, it is the terrestrial form that would eventually become a hominin calling card. And compared to life in the trees, life on the ground in Kenya during the Early Pliocene when Orrorin tugenensis’s more terrestrial descendants ambled through both the trees and the bush was a horror show. While modern lions and leopards had not yet emerged, predatory cats were still a menace. Panthera, the genus of bigger roaring cats, diverged from the smaller purring cats that led to cheetahs and your lazy, good-for-nothing housecat about 11 million years ago[xiii]. Over the intervening several million years between that and Orrorin, early tigers emerged. Basal or stem species ancestors of later members of Panthera like the lion-sized principialis or the leopard-like shawi may have been present in East Africa around this time[xiv]. Their feline cousin Amphimachairodus kabir certainly would have, a half ton of knife-toothed cat that would have eaten a newly bipedal, thoughtfully gesturing 100-pound hominin and asked what was for dessert[xv]. If knife-toothed and saber-toothed cats like Smilodon’s ancestor Megantereon were not bad enough, Orrorin’s grandchildrenwould have had early specimens of the so-called scimitar-toothed cats of the genus Homotherium and Lokotunjailurus to contend with[xvi]. In short, we are rapidly running out of types of swords to describe the teeth that would have been happy to scarf down an ape committed to the bipedal lifestyle in Early Pliocene East Africa.
Even so, big cats were not the worst of the realities of the ground. The largest known skull of any true crocodile belongs to Crocodylus thorbjarnarsoni, an extinct but enormous predator[xvii] found near where Orrorin’s descendants would have wandered in the Turkana Basin of Kenya in the Early Pliocene. During the initial forays into the savanna undertaken by Orrorin himself, it is possible that there were still some lingering basal caniforms, colloquially known as bear-dogs. While most known fossils in Africa pre-date Orrorin, later fossils found in Europe[xviii] suggest the potential that Amphicyon giganteus may still have been there to stalk earlier bipedal hominins on walkabout. These bear-dogs were five feet tall at the shoulder, seven or more feet long, and three-quarters of a ton of fun.[xix]. Again, it isn’t immediately obvious that the physiologically and neurologically significant adaptation of bipedalism would be particularly successful. But it was. There are several distinct schools of thought on the benefits that would outweigh these costs, from having the ability to reach higher foods, to heat regulation, to better visibility of prey and predator. Three hypotheses stand out, I think.
The first and most well-known hypothesis, first proposed by anthropologists Peter Rodman and Henry McHenry[xx] at UC Davis and later expanded by their colleagues Lynn Isbell and Truman Young[xxi], suggests that food scarcity created an ecological niche for creatures capable of traversing long distances. This period of the late Miocene (about 5-7 mya) was one of climactic change. Mean Earth temperatures around 13-15 mya, the earliest proposed date for Caliban to have lived, were the highest they have been at any point since[xxii] – some 7 degrees Celsius higher than present mean temperatures. By the time Orrorin showed early signs of obligate bipedalism in hominins about 6 mya, mean temperatures had fallen as much as 4 or 5 degrees, with much sharper temperature gradients at different latitudes[xxiii]. While temperature alone would have produced meaningful ecological change, even more change was the result of the drying that took place. The existing adaptations for fruit-eating in these early hominins would have given them access to one of the highest energy food sources in an environment of scarcity, but also one with more dispersed availability. That is, fruit resources tend toward concentrated but sometimes isolated distribution as a result of pollination requirements, seed dispersal mechanisms, and more specific soil and climate requirements than other food sources[xxiv]. This, some have scholars argued, would have contributed to the selection of adaptations for efficient long-distance travel, even if they came at all the many costs of descending from the trees[xxv]. Bipedalism would (eventually) have been exactly such an adaptation.
The second major hypothesis for the initial selection of bipedalism is that changes were likely already taking place in the social structure of hominin groups. It is a logical argument more than it is archaeological or ecological, but it remains compelling. The scale of benefit that would be necessary to overcome the initial costliness of the transition to obligate bipedalism is large enough that few beneficial adaptations would qualify. Child-rearing is one of them. When Kent State evolutionary anthropologist Owen Lovejoy published his now-famous article The Origin of Man in Science, he cast doubt on many of the ecological niche arguments put forth for hominin bipedalism[xxvi]. The climatic trends of the Late Miocene would likely have produced ‘diversified mosaics’ rather than ‘broad-scale forest reduction,’ he argued, and the contentions in favor of long-distance grasslands traversal would have been dependent on significant changes in social structure anyway to develop better strategies for avoiding concerningly large crocodiles and the like.
Instead, Lovejoy observed two special things about hominins. First, while most apes are altricial – positively useless and seemingly suicidal as infants – these vulnerabilities are worse in chimpanzees and worse again in humans and their early hominin ancestors. We also experience comparably long periods of gestation. Human women carry children more than 50% longer than macaques, for example. The period of helpless infancy is more than twice as long as that of a gibbon (in addition to being many times longer than any first-time human parent could ever have imagined). Longer gestation and altricial infancy increase ‘environmentally induced mortality,’ which is the scientific way of describing the various curious ways that organisms manage to walk into the indifferent buzzsaw of nature. Higher primates, Lovejoy notes, most successfully address those heightened mortality risks through ‘strong social bonds, high levels of intelligence, intense parenting, and long periods of learning.’ In short, infant mortality in light of comparably long altricial and gestational periods was a major problem. Adaptations which could shorten the time between births or otherwise reduce this mortality would have been very well-adapted.
Lovejoy argues that increasing tendency toward and capacity for bipedalism would have produced two early such adaptative benefits. A not insignificant share of ‘environmentally induced mortality’ was a function of quadrupedal apes being lousy at keeping hold of their babies and the rather unfortunate associated complication that they literally lived in trees[xxvii]. Yes, this is pretty funny. It is also a real thing. The ability to carry things (including babies) more safely and effectively is clear advantage of bipedal developments. That is also true for objects like food. Lovejoy’s core thesis is that this capacity would also have created a strong evolutionary pressure for the adoption of a provisioning role for males. In other words, he argues that even the earliest bipedal adaptations would have facilitated a thorough restructuring of early hominin society. Newly bipedal mothers could now safely hold, mother, teach, and intensively parent their offspring. Newly bipedal fathers could range further in search of food and successfully transport more back to mother and child, reducing mortality risks for both and increasing the success of more frequent new births. The nuclear family, pair bonding, monogamy, more fixed habitation ranges, and new social roles driven by sexual dimorphism would all have been reshaped, he argues, by the interaction of bipedalism with the existing pressure placed by the environment on hominin infant mortality. So, too, would the preference for living on the ground, where these advantages might be multiplied.
It is difficult to prove his hypothesis; we cannot ask several million year-old Orrorin whether he had a wife and kids, and how often he ventured down to the savanna. The infant mortality claim and the advantages of a secure carrying capacity are well-supported. So is the later evolution in hominin social structures, which lagely reflects what Lovejoy suggests was beginning to take place in these societies. The evolutionary question is not so much whether what he suggests took place, but rather when, where, and in what order.
To that end, the third hypothesis, while the newest, is in many ways the simplest. It casts doubt on the idea that hominin bipedalism must have evolved largely in response to terrestrial environmental pressures. In other words, it presents a theory that much of Caliban’s exile from the Garden of Eden was not an abrupt departure – that early adaptations toward bipedalism were still largely driven by the environmental pressures of the arboreal setting[xxviii]. We lived for the most part in trees, and we began to walk upright for the most part in trees[xxix]. It is an attractive theory not least because it explains certain complications in the fossil record. As I observed previously, Orrorin still possessed certain physiological structures suited for brachiation (tree-swinging), most of which were generally written off as evolutionary baggage. It is easy to think of them as vestigial traits, as holdovers from prior evolutionary states like your coccyx, wisdom teeth, and appendix.
But like the appendix, which new research indicates may serve a non-vestigial role acting as a ‘safe house’ for beneficial gut flora, physiological traits beneficial for brachiation would not have been vestigial in any meaningful way for transitionally bipedal early hominins[xxx]. Being able to hang from and function in trees would have continued to be perfectly useful. We know that in part because we can observe continued adaptations in these traits after the emergence of the traits we associate with the adaptation of obligate bipedalism. These are not neutral traits that stuck around by accident. For example, the morphology of the hand of Ardepithecus ramidus from 4.4 mya shows continued adaptation of a full range of suspensory features of the hands we would associate with modern-day chimpanzees and bonobos, millions of years after the emerge of Orrorin and australopithecine ancestors to modern Homo sapiens[xxxi]. It seems clear that it was still really helpful to be able to hang from branches for a very, very long time after hominins had begun to prefer walking on two feet. It is not at all a stretch to suppose that many of the earliest stages of human bipedal development would have taken place in the canopy of East Africa rather than on the ground – and that the nature of these first successful mutations would have been those that were well-adapted to that environment rather than the Kenyan savanna.
In a sense, this is precisely what you would expect from a process of evolutionary graduallies – a series of related adaptations whose first steps proved useful to an initial environment and later proved useful in new and unexpected ways in another environment. Perhaps more compelling than the standalone sensibility of this third hypothesis is that it strengthens rather than contradicts Lovejoy’s contentions in The Origin of Man. Both theories acknowledge the likely reality of Late Miocene Africa as a forest-savanna mosaic, which meant that building a theory on the need for long-distance travel across open expanses of savanna in search of scarce food was no longer necessary. Both theories furthermore reinforce that gathering, visibility, and carrying advantages would have combined to produce a powerful suite of adaptive benefits to bipedalism. Ease in standing on two feet makes it easier to grab things, spot things, and carry things. That is no less true in an argument for its initial development in an arboreal setting (i.e. in Drummond-Clarke, et al) than in a terrestrial setting (i.e. in Lovejoy). As it happens, physiological and cultural adaptations which reduce accidental baby-dropping and allow us to carry food to nursing mothers are evolutionarily useful in all sorts of environments. Go figure.
Some scientists have quite aggressively resisted the straw man argument that arboreal adaptation theories must oppose terrestrial theories for bipedalism[xxxii]. For our purposes, however, this is not as important. Whether we remained principally arboreal for millions of years after Caliban, and whether Orrorin himself spent much of his time there certainly matters to those interested in telling the full story of human evolution. For us it is far more important to recognize that the most credible hypotheses all identify the transformations of early hominin society, family structure, parenting, learning, and communication as fundamentally co-evolutionary processes with the adaptation toward bipedalism and the subsequent physiological and neurobiological adaptations it influenced.
It is easy, for example, to see how these changes spurred in social structure might have put evolutionary pressure on adaptations in hominin physiology relating to communication alongside morphological adaptations facilitating bipedal movement. Our ancestors in the Late Miocene and Early Pliocene would have been somewhat more capable of gesturing more frequently and effectively as habitual standers, for example, but the introduction of parenting and provisioning roles probably also would have increased the advantages of more sophisticated forms of such gestural communication associated with those roles. Bipedal locomotion would have permitted more useful long-distance carrying even in an arboreal setting, but the rewards of this on the ground as the adaptations grew more exaggerated may have been greater still. In light of the aforementioned risks of the Early Pliocene savanna, this may have created further evolutionary pressures to develop planning and communication strategies for predator avoidance, deterrence, and vigilance. Or simply for communicating more complex messages about increasingly complex human activities over longer distances.
Bipedal posture would have increased our capacity to safely hold children, but the associated increase in parenting intensity would probably have exposed children to much greater volume of communication at important developmental stages. If we are willing to use modern bonobos as a proxy, then Caliban’s earliest descendants probably experienced brief critical periods for the development of communication capabilities as well. When it became easier to safely hold infants in the trees and on the ground, perhaps our ancestors recreated the accident of Kanzi, whose presence during exposure to experimental language revealed a remarkable latent capacity for the acquisition of the structure of hominin communication.
In each such case, the rolling ball of increasing social complexity created evolutionary advantages for the selection of adaptations capable of exploiting it (and vice versa) in a self-reinforcing cycle. Capacities for tool-making, gesture, terrestriality, social complexity, and vocalization all would have been influenced by these cycles and influenced them in turn. Even if future studies prove the order of these adaptations to be just another just-so story – perhaps changes in the structure of hominin society came a bit later than I suggest here – the story of the co-evolution of human physiology, culture, cognition, and communication set off by a glorified chimpanzee with a janky hip remains true.
I think there are three features of this story that are critically important to the understanding of the tale of language and storytelling in the age of social networks. Each will come up again later in this book. The first is that culture and social structures influence the path of biological evolution. The second is that early hominins emerged as multi-modal communicators from the very start. The third and most important is that the interaction between intensive parenting, long altricial periods, and the very special human capacity for language, symbolic communication, and storytelling has been a fundamental feature of our evolution since the sons of Caliban were first sundered from one another. This would come to define how we experience, internalize, seek out, and tell stories.
But janky hips alone do not tell stories. The story we have told is that as newly bipedal creatures, hominin society adopted new social structures and new adaptations which would prove more advantageous to us in this two-legged state. Over time, this would include adaptations in the hands, the nervous system, locomotion, and the vocal apparatus. But the much more important story we must tell is the story of the mind. Because while the story of story started with the single literal step of a newly bipedal descendant of Caliban, its most important chapters concern what it was that permitted us – no, forced us – to adopt the language of consciousness.
The Pliocene Mind
If the millions of years of co-evolution of bipedal locomotion, dentition, social structure, culture, and communication were on Hemingway’s list of graduallies, both the encephalization and development of language-focused structures in the brain of the first storyteller – probably Homo erectus around 1.8 million years ago, as I will argue in the next chapter – fall pretty squarely into Hemingway’s list of suddenlies. To be fair, ‘suddenly’ is relative when we are speaking on a geologic scale. Since all adaptations begin with a single genetic mutation in a single individual, changes can emerge in small groups of creatures quite rapidly. But the scale and scope of change that would designate a new species like Homo erectus typically involve far more than a single genetic mutation, which usually means hundreds of thousands or millions of years. They also require a process of selection and propagation through a growing population of a predecessor species that over time becomes a hybridized species and then a new one. By any measure, however, the magnitude and speed of Homo erectus’s brain adaptations relative to Caliban and the hominins we know of in the years between them are striking.
In the span of the several million years between Caliban (8 mya) and the earliest known Homo erectus fossils, during that long co-evolutionary process I just described, the brains of humanity’s ancestors got bigger. A lot bigger. Using modern chimpanzees as a model, Caliban probably had cranial capacity in the range of 350-400 cubic centimeters or so[xxxiii]. Homo erectus, by comparison, had a skull that could fit a brain of more than twice the volume. And even that figure is based on the earliest Homo erectus fossils found at Koobi I in Kenya, dating to some 1.76 million years ago[xxxiv]. There are well-documented and more recent Homo erectus individuals with positively huge noggins by comparison. Sangiran 17, an excellent specimen found in Java in the 1960s, had cranial capacity of more than 1030 cm3 [xxxv]. Skull XI from the Zhoukoudian site in China was roughly the same size[xxxvi].
But size isn’t everything. The number of neurons and the ways in which they are organized are more important in some ways than the simple volume of brain matter[xxxvii]. The complexity of neural circuits, synaptic density, and the connectivity of brain regions play crucial roles far beyond simple brain volume in determining what we would call intelligence[xxxviii]. The brain’s plasticity – its capacity for reorganization – also acts as a force multiplier on the cognitive power conveyed by simple volume or mass of brain matter[xxxix]. Still, many scientists have theorized that some ratio comparing the size of an animal’s brain to its total size ought to act as a good predictor of intelligence, however they choose to define that amorphous concept. In fairness to the scientist who coined the most common measure for brain volume relative to an animal’s size – the so-called encephalization quotient (EQ) – he was also among the first to point out its deficiencies[xl]. He would not be the last[xli].
The Raccoon, for example, has a mean EQ that is closer to that of chimps than chimp EQ is to Homo erectus. Trash pandas are notoriously clever little shits when it comes to accessing any container with rotting food, but they’re not that clever. The closest they come to a capacity for grammar is eating dumpster foods in descending order of foulness. The encephalization quotient range of vampire bats begins to overlap with that of chimps, and vampire bats are not especially adept problem solvers. Their evolution involved a suddenly of its own, but instead of evolving to possess the most powerful brain in the known universe at the time like Homo erectus, Desmodontinae used its 4-million-year evolutionary sprint to become nature’s brainiest blood-sucking parasite[xlii]. Marmosets rate higher in EQ than most australopithecines would have, and they are sap-eating idiots in comparison to most other apes.
It is helpful then that many of those things which matter more than brain size alone were also adaptations that Homo erectus would have enjoyed that Caliban and his many children did not. We know, for example, that Homo erectus would have had significantly higher degrees of cortical folding, or gyrification. While we do not have intact brains from these ancient humans, we know this because endocasts can reveal imprints the folds of a brain left on the individual’s skull before the tissue rotted away[xliii]. These endocasts also reveal asymmetry in the Sylvian fissure and expansion of the planum temporale, both of which would have been critical to the storytelling and storyseeking features of the brains of both Homo erectus and modern humans[xliv].
Yet what is most interesting about the unique brain of Homo erectus is how very late in the five million plus year path from Caliban these adaptations emerged. Earlier I mentioned the archaic humans at Olduvai Gorge in Tanzania. This region gave the name ‘Oldowan’ to the industry employed by these people in the fashioning of crude stone tools. The individuals who developed this industry were active 2.5 million years ago, only a million years before Homo erectus, the first storyteller I will introduce to you in the next chapter. And yet it could be argued that in terms of brain size, density, and complexity, the species present at this site may well have been more like Caliban than Homo erectus. Homo habilis, generally thought to be the progenitor of the Oldowan industry, left skull remains at this site with mean volume of only 600 cm3. Australopithecines were present in Olduvai Gorge as well. They possessed even more limited cranial capacity. More importantly, there is little evidence from endocasts at Olduvai Gorge that the brains of any of these archaic humans had evolved in ways that produced expansion of the planum temporale, asymmetry in the Sylvian fissure, bulging in what is now Broca’s area, expansion in the prefrontal cortex, or gyrification more broadly, much less any changes in the composition, mix, nature, or properties of individual neurons or brain network structures[xlv]
Endocasts and skulls can only tell us so much, of course. There was a lot going on inside the heads of these individuals that we can never know. Nonetheless, we can assert with at least some confidence that the most significant anatomical changes in the human brain which we generally relate to language and communication appear to have emerged in the last million years of the more than 6-million-year gap between Caliban and Homo erectus. It is a suddenly at the tail end of a string of graduallies in the adaptations that would have been necessary for the emergence of the Hamlet and Iago in all of us. From a literal first step driven by emerging social structures in early hominins, evolution led humanity to its very first story.
Continue with Chapter 5.
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