Lucy’s Lullaby: How losing our grip 3 million years ago may have set us on the path to language

It was dark when the pain began, I remember that much. I blinked half-awake into an unfamiliar room, wrenched too quickly from the depth of sleep. Consciousness was reluctant, and slow in coming. The glow of the small digital clock said 2 a.m. The pain faded and sleep tugged at me. I was only just at the surface, still within its grasp. I drifted, remembering combinations of the last words I’d heard or perhaps dreamed, “Get some sleep, as much as you can. It will be the last for a long time.” Before I could sink back into the abyss, the pain returned. This time it was urgent and sharp and very real. And it had rhythm; a slow, certain mechanism like the turning of a wheel. My heart began to race.

I was awake now, truly.

I took a slow, deep breath and ran a hand over my swollen belly. There was a kick, and another. I began to hum the song I had been singing for months, the Rainbow Connection with its words of love, exploration and refraction of light. This was our lullaby. I was offering a tether of familiarity that I hoped would see us both through this. This time when I spoke, my tone was different. Lighter, reassuring, melodic.

“Yeeees, I knoooow. I’ll see you soon.”

It wouldn’t be long now, or so I thought. The hours came and went, then came and went again. Pain pinned me to the here and now, preventing sleep and a wandering mind in equal measure. Monitors blinked, midwives made notes and said reassuring things. As the amniotic fluid dwindled, the familiar dome of my pregnant form withered and the baby’s shape took on an alien strangeness. Still, nothing progressed. But when everything is new to you, it’s hard to know what is unusual. Sixteen hours had passed when the obstetrician stood at my side and informed me the baby’s head was stuck.

“We’ll have to use the sunroof,” he quipped, trying to keep things light.

“OK,” I replied, equal parts worry, gratitude and surrender.

Time moved swiftly then, the bed transfer, being wheeled to the operating theatre, the quick and practiced medical choreography under bright lights, the calm competence of the staff. My tired mind was slow to catch on to true nature of the subdued emergency, and when it did it was met with the gentle pedantry of a veteran anaesthetist: “Dear, if you are able to tell me you can’t breathe, then you can breathe.”

And then, in an instant, I had a daughter. She was out and she was mine, all bundled and perfect in my arms, bleating like a tiny lamb. I quietly began our song again. Love, exploration and refraction of light. When I spoke to her, by way of introduction, I used that slow, melodic tone. For a moment it was just us and our music. I’d all but forgotten that the surgery continued, and scarcely noticed how someone held a tiny oxygen mask close to her nose as I held her. I didn’t realise it was not normal for a newborn to bleat like a lamb. But when everything is new…

Then they took her from my arms and to another hospital entirely. It’s hard to know whether, if the birth had progressed normally, if she hadn’t become stuck, if that would have kicked her lungs into full gear and she would have immediately filled the room with a lusty cry. But this was our reality. The complications of human birth. And according to an interesting theory, it began not sixteen hours earlier, or even 9 months before that, but more than 3 million years ago.

This is the story of not one lullaby, but perhaps all of them.

**********

It begins with Family.  Or to be more precise, it begins with Tribe, which sits subtly between Family and Genus on the major taxonomic rank:

Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species

As humans (Homo sapiens), we belong to the tribe Hominini. We aren’t the only ‘hominins’ in the tribe; but we are the only ones who are still alive. The other members include our extinct predecessors and close relatives. Several million years ago, hominins began the slow evolutionary process of walking upright. The fossil record is rich with evidence for this. The foramen magnum, for example, is a hole in the underside of your skull that the top of the spinal column fits into. Humans are unique among primates in having a foramen magnum placed so centrally underneath the skull, it is one of many features that facilitates upright locomotion, making it easier to keep your head erect as you walk. By comparison, other primates like chimpanzees and apes have their foramen magnum located toward the back of the skull. Our tree dwelling common ancestor would have shared this feature. The emergence of a more centred foramen magnum sometime between 6 and 7 million years ago suggests that the shift toward bipedal locomotion had begun. Over time, a number of other changes slowly took place. Walking upright, after all, was an unusual mode of transport. It was strange, ungainly, and for a long time not very efficient. The shift towards bipedal locomotion required a whole body re-structure to provide support, balance and ease of motion. This included changes to the foot, knee, femur, the lumbar vertebrae, the curvature of the spine and the sacrum at its base, and of course, the pelvis.

There was another change, too. It’s one that you might not intuitively associate with walking upright, yet it may have played an important role in setting us on the path toward language and symphonies and quantum physics.  But we’ll get to that.

First, imagine this: it 3.66 million years ago, in what is now northern Tanzania, near the edge of the Serengeti. A nearby volcano has recently erupted, leaving a layer of ash covering the ground. It rains, and the ash becomes damp and pliant. Three hominins make their way across the landscape, heading north. Perhaps they are a family travelling together, it’s almost romantic to think so. Or perhaps they are three individuals travelling one after another. They are in no hurry. Their pace is easy. They make impressions in the rain damp ash as they go. One pauses for a moment, and for reasons we’ll never know, turns west, then resumes course and continues on beyond the ash field. Soon the ash dries, hardening like clay. Subsequent volcanic eruptions soon blanket the footprints in more ash, preserving them for millions of years. The fossilised footprints are discovered in 1978 by Mary Leakey and her team, and are called the Laetoli Footprints. They tell us this: these hominins were fully bipedal, walking upright with a heel to toe motion. The big toes were no longer recessed and opposable like that of a chimpanzee or gorilla. The feet of the ash walkers had a similar appearance to our own.

IF

The Laetoli Footprints            Image Credit: NegesoMuso CC-BY NC 2.0

 

The trio most likely belonged to the same species as the famed ‘Lucy’: Australopithecus afarensis. Lucy lived 3.2 million years ago, in what is now Ethiopia. She was a fully grown adult, but still quite small. I’m not that tall, but I would have towered over her diminutive 3 foot 7 inches. In 1974 around 40% of Lucy’s bones were recovered and we know from the position of her pelvis, her knee and ankle that Lucy was an upright walker. Although her cranium was incomplete, the pieces that were discovered gave an indication of her skull size. This, along with information provided by a number of discoveries of other A. afarensis remains, tells us that although they had begun to walk upright, Lucy’s species still had quite small brains (around 500 cubic centimetres), roughly one-third the size of the average human brain.

Lucy_blackbg (2) wikimedia

Cast of Lucy’s skeleton    Image Credit:  120 via Wikimedia Commons  CC 3.0

 

 

The point here, is that bipedalism evolved while the brain sizes of ancient hominins remained small. Yet here we are today, modern humans with lovely big brains an average size of around 1.4 kg (~ 3 pounds). They’re staggering complex, too, with around 86 billion neurons functioning in a dizzying array of neural networks. When and why did this happen?

The majority of the increase in our ancestors’ brain sizes took place between 800,000 years ago and 200,000 years ago culminating in the appearance of Homo sapiens, with our complex stone tools and eventually our iPhones. Interestingly, our brains haven’t grown since our species first appeared. In fact, they’re actually shrinking. We’ve lost about 100 – 150 cubic centimetres of brain volume since the first Homo sapiens appeared. In other words, the iPhone using brain is smaller than the stone tool using brain was. But don’t panic. It’s thought that this is most likely to do with a slight decline in overall body size compared to the first humans due to changes in environment and lifestyle. After all, brains aren’t just for puzzling over string theory and Sudoku, they also regulate body functions. Smaller bodies can be run by slightly smaller brains without sacrificing intelligence. Einstein’s brain was smaller than average, and he was also shorter than average. This body-size/brain-size connection is believed to have played a role in the initial gradual increase in brain size (between 1.8 million years ago to 800,000 years ago) that took place prior to the big brain-growth spurt. During this time hominins gradually grew bigger overall, and they were able to improve their calorie intake by using stone tools to cut meat into easily digestible pieces, which certainly would have helped fuel larger bodies and bigger energy-hungry brains.  However, the fossil evidence suggests that bigger brains weren’t only dedicated to running the increasingly demanding bodily functions of bigger hominins.  Something else was going on. Technology was becoming decidedly more complex.

A surprise discovery announced in May 2015 revealed that scores of stone tools had been found west of Lake Turkana, Kenya around six hundred miles north of the Laetoli footprints. Once again, thanks to layers of volcanic ash, they could be dated. They are 3.3 million years old. This is 700,000 years earlier than any other discovery of deliberately modified stone tools. It suggests a remarkable cognitive leap. These hominins, with their small brains, were beginning to think differently.

Unfortunately, we can’t directly examine the brains of these extinct hominins. They are lost to time. However, we can do the next best thing. Endocranial casts, or ‘endocasts’, are molds made of the brain casing of a fossilised skull, and sometimes palaeontologists can see patterns left by the surface of the brain. It’s no MRI, I’ll grant you, but it can give us an idea of brain structure and how it has changed over time. Endocasts of A. afarensis tell us that the relatively small brains of Lucy’s species were gradually taking on a new structure.

Professor Dean Falk is an evolutionary anthropologist at Florida State University, and recently at the 2015 World Science Festival, she explained that there’s an intricate link between the way stone tools were becoming smaller and more complex, and the fact that the hominin brain was becoming larger, reorganised and rewired.

The question remains: why did this happen?

Falk proposes that a critical piece in the puzzle wasn’t something we gained, but something we lost. She also believes that it has quite a lot to do with why birth is more difficult for modern humans than any other primate.

 

The Devolution of Us

Hold your hands out in front of you for a moment and wiggle your thumbs. You wouldn’t intuitively think they had much to do with walking upright, much less with the development of bigger brains.

“With bipedalism, the entire motor system rearranged,” says Falk, “and it wasn’t just feet. Hands are genetically linked.”

Genetic adaptations for walking upright led to changes in hand structure, including longer thumbs, making it easier to make and manipulate tools. But this came at a high price.

As Falk explains in her new paper in the Journal of Anthropological Sciences, “By the time of Australopithecines, hands and feet had lost important adaptations for grasping.”

Moreover, this would have had a significant impact on infants during a time when they were more helpless than they’d ever been.

We tend to think of bipedalism as an evolutionary step forward, but first steps can be awkward and hazardous. As bipedalism evolved, infants required a longer time to develop the body structures required for fully independent motion. Falk points out that we still see this in modern human babies, who take longer to hold their heads up, crawl, stand and move around than their distant primate cousins. That might not have been much of a big deal for our ancestors if it hadn’t been for those changes in their hands. It wasn’t just tree branches they needed to grasp; infants needed to hold onto their mother’s hair.

A chimpanzee mother will carry her baby in front of her up to approximately 6 months; around this time the baby is then able to climb onto her back and grasp onto her hair for long periods of time.  Gorillas follow a similar pattern.  One thing chimpanzee and gorilla mothers don’t normally do is put an infant down so they can use their hands for other things. They don’t have to.

Mother Chimpansee walking by with carrying young.

Image Credit:  Andreanita copyright Dollar Photo Club

 

 

Our ancestors would have most likely still had plenty of hair to hold onto around 3 million years ago. Although there’s no consensus on precisely when hominins began to lose their body hair, genetic evidence suggests they may have been quite hirsute until around 1.2 million years ago.  So around 3 million years ago, the hair was still there, but changes to the infant’s hands and feet would have made it difficult to cling for long periods of time. Arguably, it would have been even trickier to hold onto an upright mother versus one leaning forward and moving on all fours.  We still see a grasping reflex in infants’ hands and feet today, and though we often marvel at its strength, it’s not nearly as strong or enduring as it would have needed to be.

And so, Falk proposes this: “helpless nurslings must have been carried in caregivers’ arms and on their hips and, for the first time in prehistory, would have sometimes been put down nearby.”

It seems like such an unremarkable thing to do: set the baby down for a little while so mum can rest her arms, her back; perhaps have something to eat. It sounds so very ordinary. But Falk proposes that this was a critical moment in the evolution of language and brain structure.

 

The First Conversation

Bipedal infants, who had lost the ability to grasp onto their mothers, still needed contact comfort, says Falk.

“They want to hang on, but they can’t, so there was a trend to seek contact comfort.” She believes this opened up a ‘vocal channel’ between mothers and their infants.

“It is likely that pre-historic mothers whose babies were unable to sustain clinging were the originators of stimuli that are still used to soothe and hush unhappy infants, including physical placaters (hugging, rocking, bouncing, picking them up ) and vocalizations (lullabies, shushing).” {JAS 2016}

This vocal channel, she says, could have enabled increasingly more complex give and take between mother and child, involving prolonged eye contact and vocal communication between them. She also believes that this would have played a role in the evolution of babies’ emotional crying and signals to be picked up, and proposes that this early life communication was a step on the path to early forms of language. Again, we can’t directly examine our ancestors’ brains, but we can look at the cognitive processes that take place in modern infants during this same highly dependent, pre-walking period to see where we’ve ended up. We can also look at the way we talk to babies.

Today, ‘motherese’ or ‘infant-directed speech’ persists, and it goes by many names, including ‘baby talk’. It is melodious. It’s slower. Vowels are emphasised, as are individual syllables and words. Moreover, it is a wide spread human phenomenon. Research shows that it helps babies discriminate between speech sounds, making it easier for them to break down speech into its components.  And modern human babies, in turn, are primed to process this information.  They are capable of an astounding level of statistical analysis.

 

Baby, the statistician 

Across all the world’s languages there around 600 consonants and 200 vowels. Moreover, each language has a particular set of speech sounds, called phonemes. English, for example, has around 40 phonemes and the differences between them can be incredibly small, such as the subtle but critical difference between /b/ and /p/, which can change the entire meaning of a word.

Human infants begin discriminating between phonemes from birth.  By six months they can distinguish between the 800 consonants and vowels across every language; they are learning and listening, their brains cataloguing patterns, noting acoustic regularities and unconsciously processing the statistics of everything they hear. As Moti Lieberman of The Ling Space points out, if they weren’t doing this, they’d be making way more mistakes when they start speaking than they actually do. By 12 months infants have honed in on their own language; they lose the ability to distinguish phonemes of other languages but can hear and process those in their own language extremely well. We hold onto these phonemes so tightly, says Lieberman, that when we learn other languages as adults, we tend to bring our accents with us.

Research by Professor Patricia Kuhl at the University of Washington and her colleagues shows that these linguistic processes are given a boost by the brain’s reward systems, highlighting the importance of social interaction in language acquisition. Interactions such as the mutual gaze between parent and infant, as well as the child’s ability to follow the parent’s gaze provide social cues that boost comprehension. As Kuhl explains in her recent overview for Scientific American, the result is “a mastery that occurs more quickly than any complex skill acquired during the course of a lifetime”.

And so, we have gone from an early ancestor infant who was physically a late bloomer who could no longer hold onto its mother to a human infant who is still quite functionally helpless in the first year, but who can now process a stunning array of linguistic information. Falk reasons that the development of give and take communication between caregiver and infant would have helped compensate for that lost-grip and longer physical development; and it would have conferred a survival advantage. Moreover, she hypothesises that it could have triggered the development of larger, more complex brains.

This is because brain research that compares hummingbirds to whales, and humans to other primates tells us that as brains change size, they tend to do so in a coordinated manner. They grow as a whole, not one section at a time. Falk puts it another way: for the brain structures related to a particular behaviour (like the emergence of language) to get bigger, the rest of the brain must become bigger, too. Evolving larger, more complex neural networks to facilitate the parent-infant communication in the first year of life, she argues, could have set the ball rolling for a brain that became bigger and more complex over time.

Naturally, there’s a catch.

 

Birth of a big brain

The fastest growth of the human brain takes place not only in the first year of life but also in the last trimester of gestation. This is not seen in any other primate.

Overall, human gestation is just a bit longer than a chimpanzee’s by about 30 days. They follow a fairly similar pattern of growth and growth acceleration up until around week 22.  Then something interesting happens. In chimpanzees, brain growth starts to slow down. But in humans it does the opposite: it continues to accelerate. By 32 weeks, chimpanzee brains are only growing at 4 cubic cm per week, while the human brain is growing at around 26 cubic cm per week. The stark divergence is remarkable. Consequently, the average human is born with a brain that is one third the size of an adult human brain, and is already similar in size to that of a fully grown adult chimpanzee, and not much smaller than that of an adult gorilla.

For humans, this comes with risks.

While brain size was changing over the course of roughly three million years, so was the bipedal anatomy. It underwent its own fine tuning, evolving from the short stature and wide pelvis of Lucy’s time, to the now familiar human form. Among other things, this involved narrowing of the pelvis and, consequently, the birth canal. It was long thought that a narrower pelvis allowed more energy efficient locomotion, but a recent study suggests that this was not the case, and that a wide pelvis is just as energy efficient. As such, the evolutionary advantage of the modern pelvis is not entirely clear; it’s possible that a narrower pelvis can facilitate higher running speeds or reduce injury. Whatever the reason, the alterations to the human female pelvis coupled with infants’ pre-term cranial growth-spurt have contributed to a situation where human births are much more difficult than those of other primates. An infant with a large noggin ready for phoneme parsing is an extremely tight fit in the human birth canal. Sometimes, it simply doesn’t fit at all.

*****

It’s the next day in the maternity ward. I’ve been asking for updates as often as I can get them. I’m told my daughter has improved, her cries now full and robust. This is wonderful but bittersweet because I still haven’t held her since the moment we met. We had just that song and nothing more. I tell them that if she is to remain at the other hospital then I’m coming, too. Given my post-surgical bed-ridden state, the logistics are unclear to me, but I don’t care. Then I get the call. They’re bringing her back. I have no recollection of getting into the wheelchair, but I doubt it was graceful. Soon I’m in the neonatal ICU, surrounded by a dozen or so incubators, each containing a newborn. Tiny chests rising and falling, to each their own rhythm. Maybe it’s this that reminds me of the sea, or how precious they are, contained and watched over. They me think of ships in bottles, each with their own journey ahead. Mine is among them. It takes an excruciatingly long time to remove all the tubes and the tape. And then at last I get to hold her again, and she lays that big beautiful head of hers on my chest, and we are alright.

More than 9 years have passed since that moment. It’s a school day and she’s meant to be getting ready, but I can hear her at the piano. She’s composing something off the top of her head again and I’m elated at how random and kind of beautiful it is. I also know I will never hear it again in exactly like this, so I keep quiet and still the way you do when you’re close something you don’t want to frighten away but is not yours to keep. That’s what the music is for me, a momentary glimpse into the world inside her mind. Later we talk of where stars come from, whether pandas have whiskers and how to spell various dinosaur names (which is not easy before coffee, I might add). There’s a lot going on in there.

The evolution of the brain is itself a complex story, with many contributing factors, and that story is far from complete. So, too, the story of language. Whether it will ever be possible to identify a single trigger that started us toward language and symphonies and quantum physics is difficult to say. But Falk’s hypothesis has me intrigued. I’ll certainly never look at my thumbs in quite the same way again, nor the strength of a baby’s grasp, as well as its limits. It’s possible that the moment an infant lets go contains within it another moment millions of years old: a mother in the tall grass with an infant who is now too heavy to carry but who cannot hold on; a mutual gaze held a little longer than it had ever been before, and within it the first glimmer of a lullaby.

 

**********************

 

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Further Reading and Viewing:

World Science Festival 2015  — Planet of the Humans: The Leap to the Top

Falk, Dean (2016) “Evolution of brain and culture: the neurological and cognitive journey from Australopithecus to Albert Einstein” Journal of Anthropological Sciences Vol. 94 (2016), pp. 1-14 

Kuhl, Patricia (2015) “How Babies Learn Language” Scientific American 

Nadja Reissland and Barbara Kisilevsky, eds. Fetal Development: Research on Brain and Behavior, Environmental Influences, and Emerging Technologies. 2016.  Springer International Publishing

The Ling Space gives a good overview of phonemes and how different languages ‘carve up the sound spectrum’ [Ling space on Phonemes]

Images:

Copyright of gazing baby feature image belongs to Fiona McMillan

Copyright of the last baby image in the article belongs to Michael Webster and Fiona McMillan

10 Comments on “Lucy’s Lullaby: How losing our grip 3 million years ago may have set us on the path to language

  1. An absolutely enthralling read, well done Fiona! I really enjoyed reading this piece.

    Like

  2. beautifully written, joyous to read. lost in those blue eyes. thank you, Fi

    Like

  3. Pingback: The Best Australian Science Writing 2016 | DR FIONA McMILLAN - SCIENCE WRITER

  4. Pingback: 2. Songs of the Savannah | In the Footsteps of the Young Naturalists

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