Andrew Skeoch

author - naturalist - wildlife sound recordist

Supplementary Chapter:

The Evolution of Rhythm


Notes and References

By any biological and evolutionary measure, the rise of Homo sapiens has been an extraordinary chapter in the story of life on Earth. As much as any other, we are a sound-making species. Given how pivotal sonic strategies are to the success of other species, what can we speculate about how sound may have shaped our own?

The Colobus Monkeys of Mt. Meru

The Cape Buffalo is a massive creature, more so when viewed from close to the ground. Pulling back the tent flap and looking out into the night, I unexpectedly saw one in the torchlight grazing about twenty metres away. Fortunately, and to my relief, by the time I'd pulled on my boots and emerged into the tropical night air, it had ambled off.

We were camped in an open glade encircled by equatorial forest on the slopes of Mount Meru in Tanzania. Its sister volcano, Kilimanjaro, lay some sixty kilometres distant to the east. The previous afternoon, our driver Roger had taken Sarah and I to look out over a soda lake, to view the mountain's magnificent bulk on the horizon, rising from the surrounding plains with those famous snows clearly discernible. In the foreground, hundreds of Greater Flamingos fed on the nutrient-rich waters, occasionally taking wing in flights of delicate pink.

Returning to camp along roads through Meru's evergreen forests, we'd come across a group of Black and White Colobus Monkeys, and observed them foraging high in the tree-tops. They are handsome animals, their shaggy coats of coal black and pure white ending in a lengthy and luxuriously-furred tail. Entirely arboreal, they moved gracefully around the tree-tops, and we watched them resting sprawled lengthwise along branches, or perched high in the canopy, grooming each other while peering out at their world. Their chilled lives seemed rather admirable.

Back at camp, our cook Ally had set up our tents and was preparing dinner in a small kitchen building secure from animals. Standing in the glade as the last light of day paled into soft salmon, I became aware of a murmuring growl that seemed to emanate from far away. Puzzled, I was listening intently when the trees around us suddenly erupted with powerful, gruff voices, the air pulsing with deep, guttural growls. It was entirely unexpected, and I spun around seeking the source of this wondrous racket. Roger watched me with amusement, he wasn't letting on. Then I saw movement in the trees: Colobus Monkeys. We had a troupe of them living right above us.

Not expecting this dusk chorus, I'd been unprepared for recording it, however Roger said they'd call again just before dawn. In anticipation, I now gathered my recording gear and set off across the grassy clearing toward the forest edge. The night was still and the sky clear. Dew pattered from the tree-tops and every now and then I'd hear the eerie cries of Brown Greater Galagos, those possum-like animals also known as bush babies.

I was vigilant as I entered under the canopy into the close gloom of the forest. The Tanzanian Parks Service had allocated us a ranger armed with a rifle overnight, but he was slumbering usefully in the kitchen. I wasn't sure what I should be alert to, but I imagined the reflected shine of a pair of close-set eyes could be a Leopard. I moved slowly, sweeping my head torch methodically around me. Suddenly I saw what I feared, a pair of eyes glistening in the torchlight. I froze, but the eyeshine disappeared as the animal turned and crashed off into the underbrush. It was a Dik Dik, a gorgeous and tiny antelope, and possibly the first one of its species to momentarily terrify a human.

Around half an hour later, with the microphones placed and recorder ticking away, I noticed a first subliminal hint of growling coming from far off. It gradually grew, approaching as each troupe of Colobus Monkeys sparked their neighbours in turn, a Mexican wave of communities spaced out around the base of the mountain, each taking their turn to announce their presence.

Soon the group in the trees above me began calling, the incoming wave reaching the shore. With pulsing baritone growls, several animals joined in; RRRRAAOK, RRRRAAOK, RRRRAAOK, RRRRAAOK... These monkeys had such vocal charisma! Slight disturbances in the tree-tops accompanied their waking chorus, but after a minute or so they settled down again. Stillness returned, the tidal surge having passed on. Ten minutes later it came again, another wave of communal vocalising.

The Evolution of Rhythm

Hearing these Colobus Monkeys brought me to reflecting that we were in Africa – 'the cradle of humanity'. The mosaic of equatorial forests and grasslands around me were exactly the kind of habitat in which Australopithecines – those pre-hominin animals from which we're ultimately descended – are believed to have once lived. Australopithecines are thought to have been partly arboreal, descending from trees to walk upright, albeit still a little awkwardly, possibly across open glades in the forest similar to the one we were camped in. I imagined them, capable in the trees, increasingly confident on the ground, and ever watchful for Leopards with a similar sense of anxiety that I had.

I found myself wondering... What would Australopithecines and their later hominin descendants have sounded like? We can assume their vocalisations would have shared a common inheritance with primates. But in what way, and to what degree? Unfortunately, palaeontology gives us few clues, the fossil evidence only offering a tantalising and fragmentary picture of how ancestral species may have lived. If we only knew of Colobus Monkeys through fossil remains, we'd know nothing of their pied, shaggy coats, chilled social interactions, powerful voices and habit of chorusing so gruffly in Mexican waves every dawn and dusk. Their communicative behaviours would remain unknowable. We'd probably be able to infer they were largely arboreal, but after that we'd be guessing.

Which is what much discussion of human origins is: educated speculation. Much of this speculation concerns physical circumstances: the use of fire, a greater consumption of meat, hunting or scavenging lifestyles, tool technologies, palaeoclimates, long distance migrations, defences against predators, temperature regulation, loss of fur and the energy needs of an expanding brain. While these factors are doubtless part of our story, it was the aspects explored by Steven Mithen, professor of archaeology at Reading University, that I found particularly thought provoking. He focused instead on communication.

Mithen's book, The Singing Neanderthals, proposes hominins developed vocal behaviours that could be described as proto-musical. This idea is not particularly new, Darwin himself speculated along similar lines. However Mithen explores the subject by drawing on contemporary research.

Beginning by considering modern primates, Mithen notes how physical grooming is an essential part of daily life. As we observed at our Meru campsite with a group of Olive Baboons lazing on the grass, the intimacy involved is considerable. Few parts of the body are left unexamined in minute detail. The purpose of course is only partly to remove parasites, its greater function being to facilitate social stability and bonding. This is so important that a considerable proportion of a primate's daily routine is spent grooming companions.

Physical grooming is manageable when your family clan comprises a dozen or two animals, but some primate species live in much larger groups. For instance Geladas, an old-world monkey found in the highlands of Ethiopia and initially thought related to baboons, live in communities that may comprise up to 200 animals. That's a lot of grooming to get around to. Geladas have developed a nuanced system of social vocalisations, by which they negotiate their relationships and maintain group cohesion. They've largely replaced physical grooming with vocal grooming.

It is speculated that early hominins also lived in large communities, a beneficial adaptation to living in more open habitats. Vocal grooming, perhaps similar to the low, reassuring moans we often heard among foraging baboons, may have been part of this transition, shifting vocalisations toward increasingly sophisticated social purposes.

Murmurings of reassurance among a troupe of Olive Baboons.

Mithen then turns to the fossil evidence, detailing the way Australopithecines began, and hominins completed, the transformation to walking upright. Bipedalism required a suite of co-ordinated anatomical changes; longer legs, the configuration of toes, the angle of the hip joint opening, a lower lumbar curve with the spine becoming more upright, which in turn altered the angle of head and neck. This last realignment was significant, as it constrains the throat area, requiring the larynx to be situated further down the airway, which in turn permits a more flexible vocal mechanism. So it seems that a byproduct of walking upright was a change in the capacities of the voice, allowing greater subtlety of expression and a more melodic, less guttural tone.

Another recalibration of this transition, more profound yet not discernible in the fossil record, occurred in the brain. Watch any child take its first faltering steps, and one is aware of the mental processes involved in walking upright: balance, posture, and a fluid sense of movement. Without these, we topple. Evolving this synchronisation required development of the timing centres of the brain. Walking involves not simply footfalls, but arm swinging and counterbalancing. When this all falls into place, we have a grace of movement. And we have pacing – left, right, left, right...

To walk upright is to possess a natural rhythm.

Mithen proposes that for early hominins, this natural rhythm of brain, body and movement, plus a mellifluous vocal capacity, combined into a form of vocal grooming that could be described as proto-musical. He suggests that this change in communicative behaviour, originating as it did with bipedalism and the adaptation to a savannah lifestyle, may date to nearly 3 million years ago, and be integral with the emergence of the first species of a new lineage that has ultimately lead to us: homo. I find this an exciting possibility – once again, we are seeing a novel vocal strategy at the inception of a new taxonomic lineage.

While melodic vocalisations are found widely in nature, notably in birds and cetaceans, the capacity for rhythm is a hugely significant development. It is a completely novel sonic strategy, its implications comparable with learning in songbirds. To begin to appreciate its significance, we must first recognise that rhythm is not generally found in nature, at least not in a refined form. Perhaps this may come as a surprise, as we often talk of the rhythmic calling of frogs and insects. But we have to be clear. The essence of rhythm is not regularity of timing, but synchronisation. While frogs do co-ordinate their vocalising, it is irregular and non-metrical, and functions in the avoidance of calling together. The stridulations of crickets are triggered by a simple neural mechanism at regular intervals. While each individual may call more or less consistently, one hears stutters and erratic hesitations, and there is no synchronisation within a community. Among birds, the monotonous calls of the world's pigeons or barbets are similarly given at periodic intervals, each individual calling at its own pace, independently, drifting in and out of phase with others as they do so. Rather than rhythmically synchronised, all these vocalisations are simply repetitive.

Repetitive calling of Barbet species in a Thai rainforest

Researchers have however identified a proto-capacity for rhythm in a handful of animals, notably sea lions, cetaceans and (famously, as with Snowball the dancing cockatoo) parrots. This has prompted experiments in assessing rhythmic ability, such as introducing elephants to ensembles of jumbo-sized percussion instruments. They've been observed to take great pleasure in crashing and banging them together, however getting together on a groove seems to elude them.

Recently, researchers studying the Indri Lemurs of Madagascar identified simple rhythms in their songs. Indris are monogamous, live in small family groups, and sing antiphonally together with tonal hoots. The intervals between two sounds have been measured to have either the same duration, a 1:1 pattern, or a second interval twice as long as the first one, 1:2. The 1:1 pattern may be thought of as fundamentally a repetition, however unlike birds, frogs and insects, Indris do seem to synchronise calling among their group to this basic timing. They then add a little spice, with the 1:2 variation being analogised by researchers to the 'stomp-stomp-CLAP!' of Queen's 'We Will Rock You'. These are termed categorical rhythms, and indicate that Indris have a sense of pulse, joining the very few animals who seem to display this capacity.

Indri Lemurs are known locally in Madagascar as Babakoto, which can be translated as 'father of child' or 'ancestor'. While lemurs are primates, and thus related to us, they are only somewhat distantly affiliated, sharing a common ancestor with us around thirty million years in the past. Interestingly, while Indris display this proto-rhythmic capacity, our closest living relatives, Chimpanzees, seem hopelessly inept at rhythm (although they do show a propensity to 'dance'). This indicates that our human ability to come together on a groove, while emerging from a latent potential in nature, has evolved quite independently.

Rhythmic Entrainment and Sociality

Rhythm may be an exceedingly rare sonic strategy in nature, but why should it be a biological game-changer? Why have humans developed rhythmic capacities to a point where Freddie Mercury could so effortlessly inspire an audience of seventy thousand at London's Wembley Arena to 'stomp-stomp-CLAP!' in time? We experience rhythm as action synchronised to an internally felt beat or pulse, but the behavioural significance is profound.

When synchronising sounds, we are actually synchronising minds.

This is apparent to anyone who makes music with others. A friend of mine, Carl Panuzzo, one of the most intuitive and gifted musicians I know personally, told me of an occasion that illustrates the power of music to link minds. Carl was the drummer in a band, and on turning up to rehearsal, was told by his bandmates that they'd met a new sax player and invited him to come along. However as their guest had yet to arrive, they began playing anyway, just jamming. When he arrived soon after, he set his instrument case on the floor, opened it, calmly assembled his instrument, and joined in. They were improvising; weaving lines, listening, acknowledging, anticipating, responding to what each were doing, conceiving and adding new ideas, picking up and elaborating those already established, stepping forward at times to take leads, and then back to support. They played together for nearly half an hour, and after concluding among smiles, the new sax player came over to Carl to introduce himself. Carl told me; "He didn't need to, I already knew everything about him from his playing".

We 'play' music, 'play' an instrument, and describe a skilful instrumentalist as being a good 'player'. And herein lies the magic of music. It is play in a biological sense; a way of learning and emotionally connecting.

Emotional expressiveness is a feature of mammal communication, not found to the same degree in other creatures. Listen to mammalian voices and one can hear rich emotional lives articulated in sound. In humans, whilst we may speak with feeling, it is through music that this communication of emotion can most deeply be shared. With music, we're able to take mammalian emotional connection to an advanced level. Irrational and instinctive, music making – musicking – reveals the soul. As Carl's anecdote illustrates, our personality and character cannot be hidden in the process of making music in the way they can otherwise. Musicking is socialising.

This addresses a puzzle of early human researchers. Our closest relatives, Chimpanzees and Gorillas, live in hierarchical groups. Their positions of status prevent them from abiding on easy terms with each other. They squabble over food and mates. There are frequent disputes and physical altercations. They seem chronically unable to just hang out with each other amicably.

How did humans evolve from these primate behaviours to become one of the most truly social and co-operative species on the planet? Anthropologists have suggested a two-step process: firstly learning to overcome distrust and become 'friendly' with one another, and secondly, developing the capacity for actual collaboration.

I suggest that both steps were achieved by the emergence of new sonic strategies. The first was synchronised vocalising, with vocal grooming as a stepping off point. Opening the way for a new form of synergy, rhythm brought early hominins together, bonding families into a community, and parties of hunters into a team who knew and trusted each other. Grooving together became infectious, and rhythm a pathway to sociality.

If indeed this pivotal step began with full bipedalism, and signified the emergence of the Homo lineage, then this puts the earliest origins of the behaviour we now know as music making at possibly around 3 million years ago. From this time, the fossil record shows a steady increase in cranial capacity, slow at first but undergoing a dramatic growth spurt over the last 600,000 years. Researchers have speculated brain size and architecture were driven by the complex requirements of social interaction. I'd be specific and suggest it was communication, with the emotional play of synchronised sound making being its form of expression.

I cannot easily imagine what the vocalisations of early hominin animals may have been like. I envisage a simple expression of rhythm, yet one that could not fail to get everyone moving. Sound and dance, possibly in representation of animals or each other, would have blurred the boundaries of individuals and generated a trance-like state, bringing them together into communality. Very possibly, utilising their supple vocal abilities, their musicking would have been melodious, spontaneous and emotionally expressive, bonding clans into a knowing and trusting of one another that was vital to their survival. However if they had given voice with something like the pulsing chorus and gruff charisma that I heard from Meru's Colobus, I would not be surprised. Likely they joined their voices around the world's first campfires. Intriguingly, clans of Chimpanzees have been observed to gather, yelling out, slapping hands and banging sticks on tree trunks to create a collective ruckus. Perhaps early hominins similarly threw quite a party.

This picture suggests music as we understand it is an evolutionary development with profound consequences. Rather than a recent cultural or artistic phenomenon, it is an ancient and biological one. Music links us to the soundworld of nature, not through imitation of it, but in being a novel innovation departing from ancestral animal communications. From this perspective, the mysterious hold that music has on our contemporary minds begins to be more explicable. It also helps us appreciate why participation in musicking is so universal and important in Indigenous cultures, and suggests that we'd do well to encourage a renaissance of community musicking in our own societies.

So hominin sociality and a gradual development of higher intelligence may have been the outcome of that first acoustic innovation – synchronised sound play. The second step, taken much more recently, was a gradual transition from gestural communication to actual language. Perhaps this originated in the threat-specific alarm signals inherited from monkeys, and expanded into a far more articulate system of abstract verbal signalling.

Alarms calls from a troupe of Olive Baboons, likely in response to a leopard

Vervet Monkey leopard alarm calls

Vervet Monkey human alarm calls

Indian Hanuman Langurs, usual troupe interaction calls

Hanuman Langur tiger alarm calls

Whatever its origins, the indications are that language was initially slow to develop. Grammar and syntax allow single ideas to be manipulated and joined together to communicate far more complex meanings. A lack of innovation in stone tool technologies throughout the Palaeolithic indicates that this kind of linguistic sophistication didn't really take off until the Neolithic. Even so, if its essential form originated prior to this, possibly by around 100,000 years ago, then language may have been the sonic strategy that defined the emergence of a new species: Homo sapiens.

The Earliest 'Listening Peoples' – Our Pre-human Ancestors

With the Colobus Monkey chorus at Mount Meru subsiding, the dawn birdsong commenced. I was hearing Mountain Greenbuls, Variable Sunbirds, a distant Emerald-spotted Wood-dove, and joining in a little later with hoarse, barking calls, a group of psychedelically colourful Hartlaub's Turacos. These species, along with the Colobus, created the soundworld of an evergreen realm – east Africa's equatorial forests.

Shortly after, we decamped and moved on to experience the 'familiar' Africa; a landscape of acacia scrubs, stately baobab trees and open savannah grasslands. Here we encountered Zebras, herds of Wildebeest, Elephants, Lions and Giraffe. It was also, as I soon found, home to an entirely different suite of birdlife.

Under an ancient baobab silhouetted against the paling sky, I set up my microphones on the banks of the Tarangire River to hear this iconic environment for my first time. As the dawn birdsong began, I identified Spotted Morning-Thrushes singing in ebullient outbursts of rippling notes.

Meanwhile a variety of doves were forming a murmuring burble across the landscape. Ring-necked Doves called, oo-RROO-o, oo-RROO-o, oo-RROO-o... in evenly repeated cycles, while Red-eyed Doves sang their own pattern; u-WO-WU, u-WO-WU...

These doves formed a pulsing undercurrent upon which other species soon joined. Red-and-yellow Barbets began singing in duet with a repeated titi-kwau, titi-kwau, titi-kwau...,

and a Red-fronted Tinkerbird gave a steady pok, pok, pok, pok.... There were other voices I couldn't identify; a whistled Wi Wi weww, Wi Wi weww, Wi Wi weww..., and another bird with a somewhat mournful, upslurred note which repeated every few seconds.

An almost duck-like, nasal, waa, waa, waa... I later discovered to be a White-bellied Go-away-bird.

Then the francolins and spurfowl kicked in. They are both loud birds, their voices strident and slightly manic. The Crested Francolins were calling with a scratchy k-k-k-kraing, k-k-k-kraing, k-k-k-kraing…, and the Yellow-necked Spurfowl with a harsh series of kek, kek, kek..., each bout settling into a pattern which built to a frenzied conclusion.

The songs of so many of these species were made up of short phrases repeated over and over.

To my ear, their vocalisations wove together in complex patterns and layers. One could describe the affect as polyrhythmic, yet as I could clearly discern, there was no rhythmic synchronisation among them. Each individual bird was calling at its own tempo, all of them together creating a chaotic yet pleasing impression.
To be accurate, I'd describe it as cyclical and repetitious, and the most remarkable aggregation of such birdsong I have encountered anywhere in the world.

As the light grew, and this multi-layered tapestry continued, a new voice caught my ear. It was a reverberant, bass booming, also in a repeated pattern. Two pitches of notes alternated, higher and lower, which I later found to be female and male voices blending together to create the impression of one. These were Southern Ground Hornbills; large, terrestrially-living birds, black plumaged with red neck wattles, which we were later to encounter often as they padded around the savannah in small family groups. They are found widely across sub-Saharan Africa, making their booming voices an ever-present component of Africa's sonic landscape. Listening to them that morning, I could easily imagine I was overhearing drumming from a distant village – the hornbills sounded so evocatively African.

As our field trip progressed, I heard these repetitious patterns of birdsong as characteristic of the grasslands. Of all the planet's wild soundscapes, those of the East African savannahs are uniquely 'rhythmic'.
I was also aware that our travels paralleled the human evolutionary journey. From the evergreen forests that were once home to Australopithecines, we had, like the first Hominins, moved out into open country. Like them, we'd transitioned from a soundscape without 'rhythmical' birdsong, to one dominated by it.

I could easily imagine early hominins in those savannah landscapes. I could visualise groups of them walking through the swaying grasses, their steps falling into a natural rhythm, often synchronising footfalls with their companions. In those micro-silences between steps, they would listen around them, ears tuned to their surroundings. For every day of their lives, they would be enfolded in repetitious patterns of birdsong. Like us, they would have heard Ground Hornbills drumming each morning. In a state of sensory immersion, these sounds of the African bush would have been all our far distant ancestors knew.

Still animals, but with nascent intelligence, they would have initially vocalised non-rhythmically, like primates. Yet their patterns of easy walking movement may have naturally predisposed them to develop a more rhythmic manner of calling. As their gruff voices drifted out, they were echoed back by cyclical patterns of birdsong. It is not hard to imagine this sonic influence encouraging their rhythmic vocalisations to become more refined. As with their footfalls, they began more and more to synchronise their voices and play with sound patterns between each other. In their mammal play, they gradually became more social, not only surviving better but stimulating their intelligence. As they became natives of the grasslands, they were evolving away from their primate cousins – the Chimpanzees, Gorillas and Bonobos – each of whom continued to reside in those evergreen forests.

In being subliminally influenced by the unique sound world of their new home on the savannahs, early Hominins unknowingly began the journey that would result in humanity. As I listened to the birdsong of Africa, I sensed its long-forgotten role in inadvertently shaping their path.

Modern African musical cultures remain the most rhythmically literate and adept in the world. On our return from Tanzania, Sarah and I joined a local djembe group to learn this drumming culture. African drumming really is a language unto itself, with nuances of timing so subtle that we were struggling to even hear, let alone replicate them. As we learned traditional rhythms, I knew we were practicing drumming patterns that had been played for untold generations. And in them, I was hearing echoes of the duets of Africa's Ground Hornbills.

Audio and text © Andrew Skeoch, 2023