History makes no sense without prehistory, and prehistory makes no sense without biology.
Humans are an exquisitely intelligent and capable species of ape. Not only are our complex brains a wonder of evolution, but our bodies are engineering marvels. Our physiology has been fine-tuned for efficient long-distance running; our hands are elegantly dextrous for manipulating and making; and our throats and mouths give us astonishing control over the sounds we make. We are virtuoso communicators, with myriad forms of language, able to convey everything from physical instructions to abstract concepts, and to coordinate ourselves in teams and communities. We learn from each other, from our parents and peers, so new generations don’t have to start from scratch. Our culture is cumulative: we have amassed our capabilities over time. We have progressed from master crafters of stone tools to wielders of technologies such as supercomputers and spacecraft.
But we’re also deeply flawed, both physically and mentally. In many ways, humans just don’t work particularly well.
What do US presidents George W. Bush and Ronald Reagan have in common with actors Elizabeth Taylor and Halle Berry? They all almost choked to death on their food (a pretzel, peanut, chicken bone and fig, respectively).1 In fact, choking is the third-leading cause of death at home today.2 Compared to any other animal, we seem breathtakingly inept (literally) at the key survival skill of eating without accidentally killing ourselves. The reason for this relates to the changes to our throat that enabled us to form the complex sounds of speech and so become such expressive vocal communicators. During the evolution of our species, the larynx rose higher in the neck and changed its structure to allow more control over sound generation. In all mammals, the pipelines for breathing and eating share a short section of the same tube, with a small flap called the epiglottis serving as a trapdoor to close off the windpipe when swallowing. But the remodelling of the human throat significantly increased the chances of food getting stuck in the windpipe.3 As Darwin noted: ‘Every particle of food and drink which we swallow has to pass over the orifice of the trachea, with some risk of falling into the lungs.’4
This is only one of a number of basic design flaws in the architecture of the human body. We evolved to walk upright, but the posture puts huge strain on our knees, and back pain strikes most of us in our lifetimes. The wrist and ankle joints contain pointless vestigial bones that restrict movement and render us susceptible to twists and sprains.5 We have a number of nerves that take ludicrously long and indirect routes through the body, as well as muscles that no longer serve any purpose (such as those used by other animals to twist their ears). The light-sensitive layer at the back of our eye – the retina – faces back-to-front, leaving us with blind spots in our vision. We’re also riddled with defects in our biochemistry and DNA – data-corrupted genes that no longer work – which means, for instance, that we must eat a diet more varied than almost any other animal to obtain the nutrients we need to survive. And our brains, far from being perfectly rational thinking machines, are full of cognitive glitches and bugs. We’re also prone to addictions that drive compulsive behaviour, sometimes along self-destructive paths.
Many of these apparent faults are the result of evolutionary compromise. When a particular gene or anatomical structure is needed to satisfy several conflicting demands at the same time, no one function can be perfectly optimised. Our throats must be suitable not only for breathing and eating, but also for articulating speech. Our brains need to make survival decisions in complex, unpredictable environments, but they need to do so with incomplete information and, crucially, very rapidly. It is clear that evolution strives not for the perfect, but merely the good-enough.
What’s more, evolution is restricted, in finding solutions to new conditions and survival problems, to tinkering with what is already at its disposal. It never gets the chance to go back to the drawing board and redesign from scratch. We have emerged from our evolutionary history as a palimpsest of overlaying designs, with each new adaptation modifying, or being built on top of, what already existed. Our spine, for instance, is poorly conceived to support an upright posture with a large head on top, but we had to make do with the backbone handed down to us from our ancestors who walked on all fours.
To be human is to be the sum total of all our capabilities and constraints – both our flaws and our faculties make us who we are. And the story of human history has played out in the balance between them.
We migrated from our evolutionary cradle in Africa to become the most widely distributed terrestrial animal species on the planet. Around ten millennia ago, we learned to domesticate wild plants and animals to invent agriculture, and out of this grew increasingly complex social organisations: cities, civilisations, empires. And over this whole, staggering breadth of time, through growth and stagnation, progress and regression, cooperation and conflict, slavery and emancipation, trading and raiding, invasions and revolutions, plagues and wars – through all this tumult and fervour, there has been one constant: ourselves. In almost all key aspects of our physiology and psychology, we’re basically the same as our ancestors living in Africa 100,000 years ago. Across cultures worldwide there’s a wonderful diversity of beliefs, practices and customs, but while there are superficial differences in our appearances, and more significant genetic variations, to all intents and purposes we are built identically. The fundamental aspects of what it means to be human – the hardware of our bodies and the software of our minds – haven’t changed.
In this book, I want to take a deep dive into human history and explore how our fundamental humanness has expressed itself in our cultures, societies and civilisations. How have different quirks of our genetics, biochemistry, anatomy, physiology and psychology manifested themselves, and what have been the consequences and ramifications – not just in terms of singular, momentous events but for the over-arching constants and long-term trends of world history?
As well as the idiosyncrasies of our humanity, we’ll explore what we share in our body and behaviour with other animals. Much of our refined culture and society is no more than a thin veneer over our inherent animal nature. We are often no different from other beasts when it comes down to competing for resources and sex or trying to give our children the best chances in life. These primal drives have manifested themselves through history in everything from our family structures to the efforts of royal dynasties to control their bloodlines. We’ll take in the latest research in anthropology and sociology, and also see how many aspects of our everyday lives are deeply rooted in our biology.
Many of the requirements and restrictions of our bodies are obvious. We can survive within only a certain range of temperatures, and the efficiency with which our lungs can extract oxygen from the air limits how high we can live. (The highest permanent settlement today is the town of La Rinconada, at 5,100 metres of altitude in the Peruvian Andes.) Our need for a constant intake of water and nutrients to survive also determines the environments in which we can permanently settle. Our inability to drink seawater has historically limited oceanic voyages that relied on supplies of fresh water. Our life cycle, with the long period of development before reaching sexual maturity, governs how quickly we can reproduce and grow populations. Our bodies are vulnerable to being invaded by microscopic organisms and other parasites, which can have fatal consequences. The force our muscles can exert limits the achievements of our labour and has driven us both to harness beasts of burden such as the ox, camel and horse and to develop technology. And our need to sleep dictates the activity cycles of society.6
But features of our body have influenced human cultural development – the customs, behaviour and skills that we learn from each other – in more subtle ways as well.
All spoken languages use intricate sequences of sounds created by our upper respiratory tract: air is exhaled from the lungs, and the vibrations of the vocal cords are modified by our throat, mouth, tongue and lips. This sophisticated capability for vocalisation is considered one of the defining characteristics of our species.
Speech is composed of a series of open sounds or vowels – such as ah, ee, oo – interspersed with a greater diversity of consonants: collectively, these are the phonemes of language. Consonant phonemes can be created in a large variety of ways: the plosive release of air for a ‘p’ or ‘t’; the fricative restriction of airflow within the mouth for ‘f’ or ‘s’; the steady airflow around the sides of the tongue for ‘l’; the nasal resonance of ‘n’. All the world’s languages are composed of a total inventory of around 90 different sounds, although most don’t use more than about half of them;7 English, for example, is composed of around 44 discrete phonemes.8 By far the most common consonant sound in human speech is ‘m’, which seems to be the simplest to form. It’s used in 95 per cent of the 450 languages studied in detail by the UCLA Phonological Segment Inventory Database (UPSID) – from Abipon to Zuni (and including!Xu).9 This widespread phoneme is produced by bringing both lips together and sending air through the nose, and it is similar to the lip-smack behaviour of chimpanzees and other primates.10 It’s the phoneme that begins one of the first words ever spoken by over 5 billion of us: a linguistic variant of ‘mama’. Thus all languages around the world are dominated by the sounds we find easiest to produce – by the anatomical limits of being human.
Some features of our bodies have profoundly influenced not only what we’re physically capable of but how we think about the world. The fact that we have five fingers on each hand (and five toes on each foot) – that we are pentadactyl – is an evolutionary happenstance that became fixed in our fish-like ancestors around 350 million years ago. (It is shared by all other four-limbed vertebrates, from crocodiles to birds to dolphins.) But it has come to have profound implications for our conception of numbers and numerical calculation. We have ten digits to count on, and so most ancient cultures around the world adopted a base-ten numerical system.fn1 We think in round numbers of tens or hundreds or thousands – rather than in multiples of, say, six, 36 and 216, as we might if we were tridactyl. By the fifth century AD, the Indo-Arabic numeral system had devised the place-value notation which then developed into modern decimal numbers and the metric system for measurements. Our entire conception of mathematics is ultimately founded on the number of digits that sprout off our forelimbs.
Other aspects of the world we created are inextricably linked to our anatomical traits too. The beat of the second is roughly equivalent to our resting heart rate; the inch was traditionally the thickness of a thumb; and the mile was defined as a thousand Roman paces and thus the composite of our base-ten counting system and the length of the leg.
As we’ll see, it’s not just our physical features that have left indelible marks on our world. Our evolved psychological mechanisms and predispositions have influenced human culture in very particular ways. Many of these are so deeply ingrained in everyday life that we tend to overlook their biological roots. For example, we have a strong tendency towards herd behaviour – fitting in with those in our community by copying their decisions. In evolutionary terms this has served us well. In the natural world full of dangers, it is probably safer to follow everyone else, even if you’re not convinced it’s the best course of action, rather than risk going it alone. Often, even if we feel we’re right, we are loath to stand out from the pack. Such herd behaviour is a way of crowd-sourcing information – others may know something we don’t – and can serve as a quick judgement tool, allowing us to economise on the time and cognitive effort in deciding everything for ourselves from scratch. For example, walking through an unfamiliar city looking for a good place for dinner, we’re naturally drawn to the busy restaurant rather than the empty one next door.
This herding bias has caused the surges of fads and fashions throughout history. It influences the adoption of other cultural norms, religious views or political preferences as well. But the same psychological bias also destabilises markets and financial systems. The dot-com boom of the late 1990s, for instance, was driven by investors piling in to back internet companies even though many of the start-ups were not financially sound. Investors followed one another, assuming that others had a more reliable assessment or simply not wanting to be left behind in the frenzy, only for the bubble to burst and stock markets to fall sharply after early 2000. Such speculative bubbles have recurred through history since ‘tulip mania’ in the early-seventeenth-century Netherlands, and the same herding behaviour is behind modern boom and bust cycles such as in cryptocurrency markets.
This book is the third in a trilogy of titles – each of which can be read separately – in which I wanted to explore the grand scale of history and the making of our modern world from a different angle. The first was The Knowledge: How to Rebuild Our World from Scratch, which used the conceit of a manual on how to reboot civilisation as quickly as possible after some kind of apocalypse. It used the notion of the loss of everything that we take for granted today to peer behind the scenes of the modern world, explore how it all works and reveal how different discoveries and inventions enabled humanity’s progress. The second book, Origins: How the Earth Shaped Human History, zoomed out and explored how features of the planet we live on – from plate tectonics to climate belts, from mineral resources to atmospheric circulation – have profoundly influenced the human story. Origins took us from the emergence of our species in the giant crack of the East African rift valley, through millennia of rising and falling civilisations and empires, right into the modern world, showing how the distinct fingerprint of the natural world can be discerned even in politics today.
What I want to do in this book is extend this line of inquiry and put the focus on us – to tell the human story from the perspective of biology and the essence of what it means to be human. I am a biologist by training, and so for me this represents something of a return to my home turf. I’m hoping to reveal the profound and often surprising ways in which intrinsic aspects of our anatomy, genetics, biochemistry and psychology have left their mark on human history.
We’ll explore how romantic love and the human family developed as a consequence of our quirky evolution, and how marriage came to be exploited as a political tool by ruling dynasties. Why were European royal families particularly prone to unreliable reproduction, and how did other dynasties solve the problem – in the process creating sterile soldiers akin to those of ant colonies?
We’ll take a detailed look at how our vulnerability to infectious diseases has played a multitude of pivotal roles in the history of the world. How did endemic diseases lead to the political union of England and Scotland or help double the size of the United States overnight? Epidemics helped the spread of a once-obscure religion and ushered in the decline of feudalism but also drove the transatlantic African slave trade to the Americas.
Fundamental features of human populations such as growth rate and the balance of males and females can have far-reaching consequences, and we’ll explore the effects of such demographic forces. We’ll also discover ways to alter our state of consciousness, and how by affecting our minds psychoactive substances came to change the world. We’ll explore how alcohol became an intoxicating social lubricant, the stimulating impact of tea and coffee, the invigorating moreishness of tobacco, and how the poppy was wielded as a tool of imperial subjugation.
Errors in our genetic code have far-reaching ramifications. We’ll see how a rare mutation that arose in Queen Victoria had disastrous consequences for the ruling dynasties across Europe a century later and also had a hand in the Russian Revolution. Another defunct gene, shared by all of humanity, played a defining role during the Age of Sail and inadvertently led to the emergence of the world’s most notorious criminal organisation.
Finally, we’ll explore the wide-ranging consequences of bugs in our mental software. Which particular cognitive bias gripped Columbus, was a powerful factor that led to the invasion of Iraq half a millennium later, and today lurks behind the problem of political polarisation? Which other mental glitches resulted in the disastrous Charge of the Light Brigade in the Crimean War and today haunt international trade negotiations and territorial disputes such as that between Israel and Palestine?
But we’ll start by examining our evolution and see why, long before we cultivated wild plant species and tamed wild animals to create agriculture and civilisation, we first had to domesticate ourselves. How did humans develop to coexist harmoniously in larger and larger populations and cooperate successfully on shared ventures?