Chapter 3: Caliban’s Garden

This is Part 4 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 here, Part 2 here, and Part 3 here.

It is poetic, I think, that humanity’s oldest surviving stories are about how we became storytellers. When the Yahwist wrote of a man eating from the Tree of Knowledge of Good and Evil, he described him standing at the precipice of understanding the true nature of himself and the world. It is a creation story, of course, of the sort that exists across every human culture and of the sort that would have been told and retold long before we gained the capacity to write it down. Most humans see the patterns of creation stories because we have heard them so many times. Even more because our cultures are suffused with symbol-rich stories of how our world began. But mostly we see the patterns of creation stories because of a conscious mind that has evolved to seek them out.

Richard Dawkins and evolutionary biologists of a similarly antagonistic bent toward religious belief have stridently asserted a byproduct case for the predisposition toward belief in a god or gods who created our universe [i]. That is, they presume we seek out God as an accident of some more useful adaptation from millions of years ago. The brain has specific neural circuits that process and respond to novel or unfamiliar stimuli as potential threats[ii], so perhaps through evolution we came to possess a fear of the unknown[iii] that we calmed with gods and ritual. Maybe we are predisposed to abstract away the uncertain details of the world that might otherwise prove cognitively paralyzing. ADHD as a defense mechanism, lest we gaze too long into the abyss. It might be that an instinct toward temperance and self-control proved an occasionally well-adapted trait[iv] which also just so happened to spawn a predilection toward religious belief mandating such behaviors. Some proponents of a theory of mind – the idea that a key evolutionary mechanism for the anatomically modern human was the capacity to form predictions about other people’s thoughts – have suggested there is a curiosity about cause and effect built into those adaptations. Perhaps this is why we constantly generate predictions and causal explanations for other phenomena[v]. It is easy to see how this might also influence us to seek stories about creation, especially if we could ascribe those predictions and causal explanations to another mind – one like, say, that of a god. Or God.

Yet the Tree and the Apple are far more than elements in a creation story. They are far more than complex symbols which mean something about sin, the fall, and how evil entered the world. They are a coming-of-age story, not for a man but for mankind. To eat from the Tree of the Knowledge of Good and Evil is to become conscious. It is to become capable of abstraction. It is to become a promiscuous teleologist[vi] who cannot help but wonder at the purpose of the tree, the seemingly arbitrary rules of the Garden, and the local custom of going on walks while giving one’s dangly bits a good airing out. Even our holiest stories are not immune to the charm and good taste of a solid reference to genitalia, you see.

The story of the Garden of Eden is certainly about all those things. It is also about how we assumed our mantles of Iago and Hamlet – of storyteller and storyseeker. The primeval garden story is neither the only nor the first to tell us about how we assumed these mantles. In the even earlier story of Enkidu, we learn about a friend of Gilgamesh who ran with the beasts until he was given language and the habits of man. While perhaps not as well-known as the Genesis story, this origin story of man-as-storyteller from the Epic of Gilgamesh may be an even more direct analog. What transforms Enkidu from a fur-wearing, forest-dwelling, grunting beast is not a fruit. It is not a snake. It is not looking down like Adam to see that our recurring nightmare of forgetting to put on pants before we left the house came true. What transforms Enkidu forever is procreation. Sex.

Sex also transformed man. It is through reproduction that our genes are passed on and through reproduction that new mutations in our genes emerge. Those mutations are tested by nature in a process we call natural selection. About 6-12 million years ago (mya), surviving mutations in different populations of an ape species caused a divergence between the genetic paths that would lead to Homo sapiens and those that would lead to modern chimpanzees. Scientists arrived at that date range using simple models that rely on mutation rates and typical generation lengths[vii]. Yet hybridization among still-diverging species is surprisingly common in nature[viii]. Not to be indelicate, but your ancestors were not always picky about how genetically similar their sexual partners needed to be. Or how dissimilar they needed to be – useful context if you happen to be a member of a European royal family. Speciation – a rough estimate of when our ancestors clearly became a new species that was not a chimp and not a chimp hybrid – had probably taken root by the more recent end of that range. Perhaps 8 million years ago or so[ix]. It isn’t particularly important to our story to be precise about when during this period this ancestor may have lived. Whether it was 8 or 12 million years ago, the evolutionary and ecological questions of relevance begin in Late Miocene Africa with the split of humans and chimps. Instead of the ‘Chimpanzee-Human Last Common Ancestor’, let us call this great-grandfather of ours Caliban after the half-man, half-beast of Shakespeare’s Tempest, a mute ultimately given agency through the gift of language.

An Elizabethan Enkidu, as it were.

Perhaps a half million generations form the bridge between Caliban and you. I will argue in subsequent chapters that by around 1.8 mya, the adaptations which survived the ongoing process of natural selection had empowered some in that line of descendants to think in the abstract and to communicate and create using symbolic references. These ancient humans became the first to tell stories and the first to seek them out. These impulses and capacities were probably the product of both continuous and discontinuous evolutionary processes. Or, to adapt the immortal words of Hemingway through his character Bill Gorton, humans became storytellers in two ways: gradually, then suddenly.

We must now tell a story of both how and why. How did we follow the path of evolution from our split with the chimpanzee to this newly symbolic man of a million-and-a-half years ago? And why would nature have selected these adaptations? Some of this story may be told through facts. Mostly that means that we can learn certain truths from the fossil record. Some of the story must be circumstantial, informed by the logical evaluation of archaeological facts and what we know about evolutionary processes more generally. It is difficult, fiendishly tempting, and often misleading to look at even a significant observable physiological adaptation and conclude that it was singularly responsible for some trait or tendency of a species. That is especially true for the brain. Much of its final structure is the result not of genetic determination – the idea that your genes might provide a functionally complete schematic – but of something very much like evolution that takes place among and between neurons during your lifetime. A genetic mutation affecting an area of the brain or types of neurons cannot help rippling through other neural structures. There are several such complex adaptations relevant to the emergence of the Iago and Hamlet in each of us. All are indispensable parts of our tale and indispensable steps on the path to a modern notion of human consciousness.

Yet we must also concern ourselves with the co-evolution of social structures, language, and story alongside those anatomical adaptations. We focus a great deal on how miraculous the human capacity for communication seems. And with good reason. The ability of human children to acquire language is astonishing and has no parallels in nature. Yet that understandable focus sometimes leads us to place excessive emphasis on theories for the biological evolution necessary to produce human language. Noam Chomsky proposed the hard wiring of language, syntax, and grammar into our brains from infancy in a theory called Universal Grammar [x]. Eric Lenneberg provided many of the biological explanations for the language acquisition device that would be necessary to support Chomsky’s theory[xi]. We cannot dismiss these theories entirely, especially since Homo sapiens certainly possesses a wide range of neurobiological adaptations which contribute to the comprehension and production of language. However, we often ignore the far greater capacity of language, symbols, and stories themselves to adapt to the properties of human cognition and learning. Or at least we did until the pioneering work of scholars like Brian MacWhinney, Elizabeth Bates, and Terrence Deacon that will feature prominently in the coming chapters. Still, neurobiological, linguistic, and cultural adaptations alike are necessary Narrative elements in our tale. But with all these co-dependent evolutionary drivers of human storytelling, where do we even begin?

Caliban

There is a story to be told about how Caliban in the Garden became each of us doom-scrolling on social media, but it doesn’t begin how you might think. We tell most stories today through writing, a technology still at least 8 million years away when Caliban walked the Earth. Others we tell through spoken language, which was…well, also roughly 8 million years away. We cannot begin there. We cannot even begin with our capacity for vocalization since most of the evolution of the human vocal apparatus appears to have begun in earnest closer to 2.5 million years ago, if not more recently still. It is an attractive notion to start with the brain, which has more to do with storytelling than any other human adaptation. But there, too, we could progress through millions of years of pre-history before we found anything that looked more like modern Homo sapiens than Caliban himself. The most important adaptations to language and storytelling appear to have emerged beginning somewhere around 1.8 million years ago. No, this journey must begin as all journeys do: with a single step. Literally. To tell the tale of man as storyteller, we must first tell how he learned to walk.

Caliban was not bipedal. He could almost certainly walk on two legs, of course, but that would not have been his primary means of getting around. The preference for walking on two legs, which usually makes other forms of locomotion a pain in the ass (and back and neck and hips), is what scientists call being an obligate biped. Scientists have found a range of fossils from hominins which might have lived around the same time and place as Caliban, and the earliest are universally brachiating and/or quadrupedal. That means that their physiology was designed to move them around by swinging from trees or walking on front knuckles. But around the time that human and chimp lineages diverged, evidence of gradual change was beginning to emerge. For example, Sahelanthropus tchadensis, better known as Toumai, probably lived about 7 million years ago around the border of modern-day Chad and Niger [xii]. Toumai might have been an ancestor to Caliban, but it is more likely that he was a grandson, nephew, or cousin. The earliest studies speculated based on available fossils that Toumai might have walked on two feet like us. Most of this speculation was based on a skull with an opening perfect for the kind of spinal cord we know to be more consistent with the posture of bipedal locomotion. More recent work on other fossils has cast some doubt on that claim. Some scientists contest the nature of the opening in the skull[xiii], while others found leg bones still more consistent with an arboreal preference – that is, mostly living in trees[xiv]. Toumai was probably not the first obligate biped.

Two thousand miles to the east and a million years later, another hominin called Orrorin tugenensis might have been. He was probably a descendant of Caliban. He may even have been your ancestor. It is more likely, however, that he is a sort of great uncle, part of another branch of hominins born some point after we split from chimpanzees. That conclusion is based largely on two features of the fossils: teeth and hips. Orrorin had teeth with thicker enamel, molars meant for grinding[xv], and less prominent canines than other non-human apes, including chimpanzees[xvi]. More importantly, however, Orrorin possessed an adaptation called an obturator externus groove[xvii] and femur morphology consistent with bipedal locomotion. Basically, Orrorin had hips built to walk on two feet by default, and its femurs bore so much similarity to those of Homo sapiens that their discovery caused some scholars to consider that australopithecines – the biggest ‘missing link’ species between Caliban and you – might not be our ancestor at all, but rather a side branch of the hominin phylogenetic tree[xviii]. Subsequent analysis of how hips would have produced locomotion casts doubt on such a grand claim[xix], and there are features of Orrorin physiology like the shape of the bones after the last joint in each finger which still seem engineered for tree climbing. For that reason and others, I think we can conclude the expansion of bipedalism falls rather more in Hemingway’s compendium of evolutionary graduallies.

Still, Orrorin is the best candidate we have found for the first hominin to stand on its own two feet – habitually, anyway. Whereas the brain’s importance to storytelling, symbolic thought, and language is self-evident, if you find yourself questioning why you are reading about bipedalism, I understand. Part of the reason it is important is that how humans walk, like how we think, is one of the distinguishing traits of humans relative to other great apes. Nearly all our living relatives, including chimps, are habitually arboreal or otherwise quadrupedal[xx]. Literal knuckle-draggers. None are obligate bipeds like us, however much they may demonstrate bipedal behaviors in certain contexts.  

Bipedal locomotion is by no means incontrovertible evidence of the place occupied by any species in the hominin family tree. Creatures often develop similar adaptations to comparable environmental challenges in a process called convergent evolution. When they aren’t flying, birds are obligate bipeds just like the theropod dinosaurs from which they are descended. So are kangaroos and wallabies. A couple species of mice and pangolins, too. There are other species that move on two legs for short distances and limited purposes, but otherwise this is basically the extent of living obligate bipeds. This doesn’t mean we are all closely related, however much we might adore pangolins. It just means we faced similar environments and that nature selected similar mutations that were well-adapted to those environments. Both dolphins and sharks evolved to possess fin-like structures, for example, but not because they are closely related. Their last shared ancestor lived at least 439 million years ago[xxi], around twice as old as the oldest dinosaur. Yet there is something intrinsically useful about a fin in water that causes them to be selected in unrelated aquatic species. So it might have been for bipedalism within some ecological niche occupied by various archaic humans and archaic chimps in the Late Miocene. It is entirely possible that multiple apes before or after Caliban experienced similar evolution in leg and hip morphology in response to the same pressures. As far as we know, however, among primates obligate bipedalism is a peculiar feature of humans and our nearest ancestors. As a result, adaptations toward obligate bipedalism are circumstantially useful to scientists who are trying to understand where genetic lineages probably diverged.

For our purposes, the rise of bipedalism is doubly interesting because its emergence in archaic humans predates and then begins to overlap with other evolutionary changes important to human language and storytelling. We don’t have enough fossils to know what else may have been happening with Orrorin. We do know that Australopithecus afarensis – almost certainly part of your genetic ancestry – had a slightly larger skull and more brain matter than modern chimpanzees. It was the beginning of a process called encephalization, or the growth in the brain mass of a species relative to its overall size. Paleoanthropologists have found afarensis fossils from Tanzania, Kenya, and Ethiopia that are nearly 4 million years old[xxii], which would place these fossils about halfway between Caliban and you.

Over the next few million years, bipedalism and encephalization would, in turn, overlap with evidence of the expansion of existing and new structures of the brain we now know are related to producing and understanding language. This evidence, too, begins to overlap with adaptations of the vocal apparatus that start to look more like that of Homo sapiens, and then with anthropological evidence of social organization, creativity, and a much more sophisticated kind of thought. But is this a coincidence? Does the fact that adaptations related to bigger brains, expanded language-related brain structures, bipedalism, vocalization, artifact production, and social organization seemed to evolve together really mean anything? Do they merely overlap or is there a mutual causal relationship among them?

Yes! Well, probably. In our story, Caliban stands – or hangs – at the inflection point of significant evolution within each of those capacities. Using modern members of the genus Pan as a model, Caliban might have been capable of associating symbols with words or concepts – if there had been anyone alive capable of producing them. He might have possessed the limited capacity for more human-like imitation, as distinguished from the simple mimicry of most apes. In the right circumstances, he might even have been able to learn the structure of the most basic grammar and syntax of human language. Such a feat would allow new words and ideas to be much more readily placed within that structure, and one which until recently would have been considered the unique province of Homo sapiens.

Everything I just listed was among the achievements of Kanzi, a very real and particularly talented modern bonobo. Yet much of what he achieved was the result of almost accidental exposure to high volumes of human language and teaching during his comparatively brief period of infancy. Caliban would not have enjoyed the benefit of these external stimuli. It probably wouldn’t have mattered very much. Even Kanzi, for all his advantages, lacks the capacity to produce tools at anywhere near the proficiency we would later observe from Homo habilis about 2.5 million years ago[xxiii]. Maybe not even the Lomekwian tools produced by more primitive hominins some 800,000 years earlier[xxiv]. He cannot create novel symbolic expressions spontaneously, understand sentences with more than the simplest ordering of words, or produce the recursive properties of language. We cannot be certain, but it seems likely Caliban and other early members of archaic human lineage would have possessed similar faculties and limitations[xxv].

Like other great apes, Caliban probably possessed formidable episodic memory, which allowed him to recall specific events from past experiences[xxvi]. This means that he might have remembered individual episodes, such as where he found food, interactions with other troop members, or specific tools they used. What he lacked that humans possess is our vast capacity for semantic memory, which is the ability to store and retrieve general knowledge about the world. That may include things like raw facts but also conceptual abstractions and meaning attached to those facts. This would have had a powerful and obvious effect on Caliban’s cognition. His episodic memory would have enabled him to navigate his environment and social structures effectively, utilizing past experiences to inform current behavior. However, his limited semantic memory constrained his ability to generalize that knowledge and apply it to new contexts in the way humans do.

For instance, while he might have remembered the exact location where he found ripe fruit last season, he would probably struggle to abstract that knowledge into a broader understanding of fruiting patterns of different trees or the concept of seasons. His cognition was context-specific and less generalized than that of later hominins like Homo erectus. This would have severely impaired his ability to innovate, communicate complex ideas, and develop cultural traditions in the same way modern humans do. Yet it is in Caliban’s increasingly multi-modal communication and in the earliest signs of symbolic thought and tool use that we see the seeds of something new to come.

Even in the early stages of this process, Caliban could use his facial muscles, arms, hands, legs, and toes to make gestures that would be understood by others of his species. Many of these gestures would not have been learned or taught in any way that would seem familiar to us[xxvii], even though they possessed inherited and socially reinforced components after their own fashion. Unlike those of most other animals, Caliban’s gestures would have often have been intentional, a fancy way of describing them as directed toward a goal rather than being simple emotional responses[xxviii]. It means they might convey specific messages and requests designed to be understood. It often means they were intended to change someone else’s behavior and that the communicator was willing to be persistent until he was understood – or even obeyed[xxix]. For many years, we thought this capacity to be far more common among chimpanzees and bonobos than other apes – that most other apes are best thought of as only occasionally intentional communicators[xxx]. New research is challenging this long-held assumption[xxxi].

Scientists have also revisited long-standing assumptions about the nature of ape vocalizations. Even 8 million years ago, Caliban would certainly have been capable of vocalization, but it would have sounded nothing like the voice of a modern human. Based on similarities in skull shape and cavities within the skull used to produce sound, it is likely that his vocalizations would have sounded more like those of modern chimps and other great apes. Just as primatologists long believed that members of pan were unique among non-homo apes in producing reliably intentional gestures, most also believed that all ape vocalizations – unlike gestural communication – were nearly always stereotyped. Primatologists believed that these species could adjust the intensity and frequency of some vocalizations, but perhaps not at the level of flexibility and intentionality displayed in their gestural communication[xxxii]. This belief originally extended to all apes, including chimpanzees and bonobos (and by extension, probably Caliban), but gave way over time to a belief that our cousins from pan might be uniquely capable of some intentional vocalization, too[xxxiii].

The leading hypothesis was that the neural circuitry connecting cognition to gesture in non-human apes did not connect in a similar way with the vocal apparatus. All great apes possess adequate vocal capacities to achieve significant modulation and flexibility[xxxiv], so the prevailing belief was that it was principally a missing neural link between vocalization and ape cognition rather than morphological limitations in the vocal tract that most set other apes apart from Caliban and his early hominin descendants (later hominin vocal apparatuses have evolved significantly). Emerging research into intentionality and affect present in ape vocalizations has shifted the current thinking on intentional vocalizations to include most apes – not just chimpanzees, bonobos, and the odd orangutan[xxxv]. What’s more, primatologists are beginning to explore the more fundamental question of whether primate verbal and non-verbal communication are even the distinct things we have made them for decades[xxxvi]. In short, apes are multi-modal communicators, and the story of storytelling is the story of how humans evolved to become the ultimate multi-modal communicators.

Despite these growing capacities, however, it is worth remembering that Caliban was not human just yet. His was largely a world of immediate, tangible interactions. He might greet his fellows with a series of grunts and hoots, each sound carrying a specific meaning. It might be a call to join him in foraging, a warning of a lurking predator, or an invitation to groom. His gestures were perhaps more important. A raised hand or a gentle touch spoke volumes in his social circle, conveying reassurance, submission, or a request for companionship. In his habitat of sprawling trees and hidden clearings, this grandfather to chimps and humans produced vocalizations that were adapted to the dense foliage. Loud, resonant calls traveled through the forest, ensuring his messages reached distant members of his troop. He relied on a repertoire of facial expressions—bared teeth, widened eyes, and pursed lips—to express emotions like fear, excitement, or aggression. However, he also experienced a world in which there were few abstract concepts to ponder or debate. While modern ape studies have obvious limitations, we may suppose that he sometimes planned as much as a day ahead[xxxvii], but for the most part his interactions were rooted in the present. They were focused on survival and social bonds. He rarely communicated about hypothetical scenarios or unseen entities. His world was rich in immediate, sensory experiences, and his communication was a reflection of that grounded reality. But this reality rarely unfolded on the actual ground. Most of Caliban’s experiences would have taken place in the canopy of a Late Miocene forest. But not all. There was something happening in Caliban’s society, something happening in its individual families that would change forever where and how his descendants lived.

For many years, the story went something like this: the gradual transition toward bipedalism frees a creature’s hands to do things. They are free to communicate, to point, to pantomime, and yes, to gesture. They are free to start performing carrying, gripping, toolmaking, and tool-using tasks far more regularly. Those things have a corresponding effect on how well-adapted further cognitive developments might be, especially since we believed gesture to be the primate communication domain uniquely connected to something more than delivering mere warnings and emotional reactions. We then consider the brain of an individual with a novel genetic mutation which expanded that brain’s capacity to produce finer motions in the manipulation of objects or finer motions in the production of gestures. We then consider whether that mutation would be more likely to prove advantageous to a creature which walked around on all fours or swung from trees, or one which walked upright and had free hands to make use of those new cognitive capacities.

It is an old story because it is a good story and it is a good story because it is true. Habitual bipedal species do have free hands more often, and the value of cognitive advances would have demonstrated coevolutionary advantages with gestural communication. Yet bipedal species and those on a hybrid path with an existing arboreal preference would have lived between earth and canopy, with new and different communication needs. Their capacity to carry infants, whether in the tree or on the ground, might have exerted untold influence on social structure and the value of certain kinds of communication. Their capacity to operate over larger ranges and longer distances might have changed diets, foraging strategies, hunting strategies, security strategies, social structures, and the adaptive benefits of different kinds of communication. The story of bipedalism isn’t a linear story that takes us from walking to gesturing to trolling people on the internet. It is a story of the co-evolution of hominin biology and hominin society. It is the story of a brain evolving to manage multi-modal communication.

And yet, the first steps to make us the storytellers that apes can never hope to be were the literal steps of Caliban and his descendants beginning to experiment with bipedality, even if in fits and starts. Chimpanzees and bonobos, like most apes, can be temporarily bipedal in certain contexts. That is not to say that they do not have differing tendencies. Chimpanzees tend toward more display-oriented uses of bipedalism, for example, while their bonobo cousins tend toward expressions associated with object carrying and vigilance[xxxviii]. But all members of pan vary in how and when they stand on their own two feet. Their age, sex, the availability of different types of food, whether they are in a tree or on the ground, and the social environment all interact with how and when our closest ape relatives exhibited bipedal posture and locomotion[xxxix]. We don’t know whether Caliban was more like a modern-day chimpanzee or bonobo or something more foreign still, but we do know that his descendants would be distinguished by an evolutionary cycle that began in earnest with the accelerating adoption of habitual bipedal locomotion. Alas, Caliban himself was doomed to gaze outward through the locked gates of the Garden of Eden we call the African forest canopy of the Late Miocene.

For the next few million years thereafter, a pattern of graduallies would be a defining and recurring characteristic of human evolution. Archaic humans experienced a cycle of mutually reinforcing adaptations in (1) locomotion, (2) fine motor skill-driven tool use, (3) fine motor skill-driven gestural communication, (4) vocalization-based anatomy, and (5) general anatomy, both in the brain and elsewhere. Increases in bipedal locomotion freed hands and increased the selection benefit of a wide variety of mutations, each of which would inevitably feed back into social structures and further physical and neurobiological adaptations. Many would necessarily lead to further cognitive development. After all, what is the point of being able to flake a stone with precision if you cannot imagine its prospective uses? What is the point of being able to produce and recognize finer gestures if the brain of the sender and receiver cannot process them? What is the purpose of being able to form a clear, intentional vocalization if the receiver cannot process their sounds and interpret their meanings?

As these adaptations continued to co-evolve, Caliban’s grandchildren found themselves equipped with increasingly sophisticated tools and more nuanced multi-modal communication capacities. At some point this growing complexity in physical and cognitive skills set the stage for another revolutionary development necessary for what we would today call storytelling: the further evolution of hominin vocalization from Caliban’s primitive capabilities, along with the cognitive capacities necessary to incorporate it into more flexible and emergent symbolic communication. It is not difficult to imagine the evolutionary imperative. Gestures are difficult to see in the dark[xl]. They cannot be transmitted over longer distances[xli]. The dimensions possible for speech – rhythm, pitch, and volume, among others –increase the potential complexity of its semantic content by orders of magnitude[xlii]. We know this happened at some point between 8 million years ago and 100,000 years ago – the earliest reasonable date when structured language might have emerged – but when?

By the time Caliban’s grandchildren were flaking away bits of stone to create some of the first sophisticated tools in the Olduvai Gorge of Tanzania some 2.5 million years ago, we know minor physiological adaptations to facilitate the use of vocalizations to communicate had probably taken place. In australopithecine fossils from similar time horizons, researchers found changes to auditory canals indicative of evolution toward hearing the frequencies of short-range communication over open – possibly terrestrial – spaces[xliii]. The few Homo habilis skeletal remains found demonstrate flexion at the base of the skull first thought to be indicative of some expansion in the range of possible vocalizations, although we have since discovered that this is not an especially reliable relationship[xliv]. The vocalization potential of our ancestors, even then, would have been limited by the relatively small adaptations that had taken place since Caliban.

What we can be confident of is that somewhere between Homo habilis 2.5 mya and Homo erectus 1.8 mya, these small adaptations to hominin vocalization capacity were becoming not-so-small adaptations. This, in conjunction with the cognitive developments we may infer from the more advanced toolmaking practices of the time, is circumstantially powerful evidence that the incorporation of vocalization into a more human-like mode of communication was beginning to take place as our timeline approached the birth of Homo erectus. “The vocal tract would not appear in isolation from a radical change in hominid communication,” as Canadian cognitive neuroscientist Merlin Donald summarized this idea especially well. “This in turn would not occur without the existence of appropriate cognitive skills.” In other words, the mutual reinforcement of cognitive, social, cultural, and language-specific adaptations meant that they were also mutually reliant. Multi-modal. There is no reason for the selection of vocal apparatus adaptations unless there were a context in which they could be put to use greater than that of mere indication or the expression of emotion. The selection of a vocal apparatus at all is by no means indication of structured language – that was almost certainly still a couple million years off. But it is a strong indication that the natures of hominin communication and social structure were changing dramatically in this period between Homo habilis and Homo erectus, and probably in some ways that relied on the far more versatile potential tool of vocalization.

It is an insight which has broader implications for the tale of humanity’s meandering figurative and literal evolutionary walk. As I have told it so far, bipedalism and upright posture gave birth to a slow process of mutually reinforcing adaptations in hominin cognition, fine motor skills, vocal apparatuses, and communication. At every stage – but especially as we approached the last 2.5 million years – those capacities reached a point where we can conclude that they were increasingly shaping and being shaped by social and cultural influences. This, in turn, accelerated cognitive growth, specific cognitive adaptations relating to communication, and even the early adaptations needed for more human-like vocalizations.

Yet there is a fundamental question we have not yet grappled with: why bipedalism? Why would I suggest that this was the boot that nudged the ball of human evolution over the lip of the hill? It is intuitive enough that walking lets us do more with our hands, and as a result our brains can think of lots of cool new valuable things to do with them, which sets off a cascade of other related adaptations that might prove valuable. Interesting, but is it enough? Even more importantly, before nature selected all those additional things to do with our hands thousands of years after bipedalism emerged, it was first a tree-dwelling version of us with a mutation in our hips with no special additional talent with our hands. It is not as if nature knew that we would develop finer motor skills over hundreds of thousands of years. Nature could not know that we would reach the limit of what gestural communication could communicate a million or two years after we began walking on two legs. It told us through life and death what mattered then and there. So why would nature select bipedalism for Caliban’s children if all its benefits were just promises from the distant future?

Continue with Chapter 4 here.

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