The Book of Humans Read online

  At the same time though, it is a book about animals, of which we are one. We’re a self-centred species, and we find it hard not to see ourselves and our behaviours in other animals. Sometimes those characteristics do have a shared origin with our own. Often they do not. Regardless of their genesis, I am attempting to demystify our own behaviour by pointing to where else on Earth we see those traits, and trying to sort the things that are uniquely us, shared with close evolutionary cousins, or just things that look similar, but are in fact unrelated. I’ll be examining the evolution of technology in humans – having mastered the crafting of stones, and sticks, and fire hundreds of thousands of years ago – and in the many other animals that also use tools. Evolutionary biologists love thinking about sex, and I’ll be delving in, not only to try to understand how we decoupled sex in all its myriad forms from reproduction, but how the sex lives of animals are also a carnival of delights that are not always simply the direct manifestation of the biological imperative to create offspring. While this is a celebration of both us and the wondrous variation in nature, we are indubitably a creature capable of less than angelic behaviour, of creating horrible nightmares – violence, warfare, genocide, murder, rape. Are these different from the often horrifying behaviours that are part of the brutal natural world, the violence and sexual practices that don’t get showcased on television documentaries? In the final part, I will be scrutinising the reasons behind the evolution of behavioural modernity – meaning the emergence of people who are like us today. Our bodies became modern long before our minds did, which is a puzzle worth examining.

  Biologists appraise the wonders of evolution, sometimes to understand ourselves, often to understand the grand scheme of life on Earth. This book is a glimpse of the epic meandering journey that every organism has made. After all, we are the only ones who can appreciate it.

  What a piece of work we are!

  The pillars of biology are firmly in place, installed over the last two centuries and tested over and over again. We have bound the principles of natural selection to genetics, in cells powered by chemistry. We have aligned these principles in history, to draw a picture of how life spread from such a simple beginning in the basement of the oceans to every inch of this planet. You might think that this means the study of life on Earth is pretty much done, and now we’re just filling in the details. But science never sleeps, because there are always leviathan gaps in our knowledge. Most of nature remains unobserved, and it continues to utterly astound us with new discoveries every day, new species, and new traits in animals and other organisms that we simply have neither seen before nor perhaps even conceived of.

  Some of the things described in the pages that follow were only discovered in 2018, the year I finished writing this book. That may mean details are scant, or have been seen only once or on a few occasions. It may mean these newly observed behaviours are outliers, truly unusual characteristics. Others might be generalisable to many species, or even all. Some may turn out to be not what we originally thought. For all the glorious documentaries that we see on television, most animals spend almost all of their lives unseen by human eyes, and live in environments that are inhospitable or alien to us. That is the nature of science: seek and ye shall find. Studying these animals is important on its own terms, and may yet provide insight into our own condition.

  Sometimes these behaviours appear to have a shared evolutionary origin with us. Others exist in non-human animals because they are clearly of great use in the struggle for existence, and have evolved many times over, just as insects, bats and birds all have wings but with little in common in their histories of acquiring flight. The philosopher Daniel Dennett calls these ‘good tricks’, meaning that they are characteristics of such benefit that they arise many times in history. Flight is a good trick, and has evolved repeatedly in distantly related creatures, but it has also evolved many times over within the same groups of creatures. Evolution can be efficient in that way: once there is a plan to make a particular trait, that plan can be deployed whenever desirable. Insect wings have come and gone dozens, maybe hundreds, of times in the last few hundred million years to suit survival in the local environment, though the genetic mechanism that underlies wings remains largely unchanged during this time. Flying is only useful when it’s useful, and it’s a costly activity, so can be discarded, and the genes filed away, when not needed, like a winter wardrobe.

  There are plenty of potential pitfalls in studying our own evolution. Just as we must be careful about ascribing similarity of function with common origins, we must also be cautious about confusing our behaviour today with a presumption that that is why the behaviour emerged in the first place. There are many tempting myths about the origin of our bodies and behaviours that teeter near the edge of pseudoscience. Let me be clear on this: all life is evolved. But that doesn’t necessarily mean that all behaviours are explained with the central idea of evolution, which is adaptation. Many behaviours, especially in us, are there as by-products of our evolved existence, and not because they have specific functions that aid our survival. This fallacy is particularly prevalent in our sexual behaviours, which we will inspect in detail. We see familiar sexual behaviours in animals, some of which are associated with pleasure in us, and some with criminal violence. No matter how neat or appealing an explanation might be, science looks to facts and evidence, and an ability to test an idea to destruction.

  Every evolutionary pathway is unique, and while all living beings are related, how each one came to be is a different story, with different pressures driving selection, and random changes in DNA providing the template from which variation, selection and evolutionary change can occur. Evolution is blind, mutation is random, selection is not.

  Error and trial is a conservative process; radical biological change normally results in death. Some evolutionary developments are clearly so useful that they never truly go away. Vision is one example. Being able to see in the oceans clearly conferred a significant advantage for whatever life form first acquired vision, more than 540 million years ago – you can see things you wish to eat and move towards them, you can see things that wish to eat you and swim away. Once it had evolved, vision spread rapidly. Since then, the genetic programme for phototransduction – that is, converting light into sight – has remained virtually identical in all organisms that can see. In contrast, a crow with a bent stick wheedling out a fat grub from the bark on a tree is a skill that has evolved entirely independently of a chimpanzee doing exactly the same thing, and has little specific genetic underpinning in common. All abilities are evolved, which doesn’t mean that they all have common roots. Unpicking and filtering the similarities and difference in behaviours that appear familiar to us is crucial in understanding our own evolution.

  We have to separate out all of the attributes discussed in this book, even though each is dependent on others. We cannot recreate the order or circumstances in which they appeared. Our brains expanded, our bodies changed, our skills sharpened and we socialised differently. We ignited sparks and lit fires, tilled the earth, crafted myths, created gods and commanded animals. The beginning of culture relied upon all of these things, powered by the flow of information and expertise. It was not an apple that gave us this knowledge – apples are a product of our own agricultural ingenuity. It was how we lived our lives. We began living in populations that grew to sizes where kin became communities, and tasks within communities fell to specialists – musicians, artists, craftspeople, hunters, cooks. In the transfer of the wisdom of these experts – in the interconnectedness of minds – modernity arose. Uniquely, we accumulate culture and teach it to others. We transmit information, not just via DNA down the generations, but in every direction, to people with whom we have no immediate biological ties. We log our knowledge and experiences, and share them. It is in the teaching of others, the shaping of culture, and the telling of stories, that we created ourselves.

  Darwin, with typical prescience, suspected that this might be the c
ase:

  Man alone is capable of progressive improvement. That he is capable of incomparably greater and more rapid improvement than is any other animal, admits of no dispute; and this is mainly due to his power of speaking and handing down his acquired knowledge.

  Crucially, we are the only species to have held ourselves up to the light, to have asked, ‘Am I special?’ Paradoxically, the answer turned out to be both no and yes.

  Over the eons, we have moved from being not particularly special animals, to thinking ourselves uniquely created and distinct from the rest of the living world, to a sort of quantum state where we can occupy both positions at the same time. What follows is a compendium of that which unequivocally fixes us as animals, and simultaneously reveals how we are extraordinary.

  1 Viruses are normally and traditionally excused from this definition; arguments rage over whether viruses are living or not, though I vacillate between not caring and thinking that for all intents and useful purposes they display the characteristics of being alive. That they cannot reproduce themselves without the presence of a cellular living entity is, to my mind, not relevant. No organism has ever existed without dependence on another. The role of viruses in evolution cannot be understated and has been a major driver of the continuation of life for its entire duration, as is discussed later.

  2 The earliest Homo sapiens are found in Morocco and are around 300,000 years old, but these are sometimes referred to as archaic, rather than anatomically modern, humans, the oldest of which are more like 200,000 years old.

  3 Or four: we are beginning to think that some women are tetrachromats, meaning that they have photoreceptors that are optimised to detect four primary colours, rather than the standard trichromatic three. The new primary colour will be in the green range.

  PART ONE

  Humans and Other Animals

  TOOLS

  Humans are creatures imbued with technology. That is a word that has taken on a specific meaning in the modern age. I write these words on a computer, with an internet browser on in the background connected via Wi-Fi. We tend to think of these types of electrical gadgets and services as being the embodiment of technology today. The science-fiction writer Douglas Adams came up with three rules concerning our interaction with technology:

  1. Anything that is in the world when you’re born is normal and ordinary and is just a natural part of the way the world works.

  2. Anything that’s invented between when you’re fifteen and thirty-five is new and exciting and revolutionary and you can probably get a career in it.

  3. Anything invented after you’re thirty-five is against the natural order of things.

  Certainly, there is a seemingly constant suspicion of new technologies in the media, especially by older people expressing concern for the young: won’t somebody think of the children?

  It is the same as it ever was. In the fifth century BCE, Socrates railed against the dangers of a new disruptive technology for fear that in young men it would nurture:

  Forgetfulness in the learners’ souls, because they will not use their memories . . . they will be hearers of many things and will have learned nothing; they will appear to be omniscient and will generally know nothing; they will be tiresome company, having the show of wisdom without the reality.

  The technology that prompted Socrates’ ire was writing. Two thousand years later, a sixteenth-century Swiss polymath, philologist and scientist called Conrad Gessner expressed similar angst at the potential of another innovation for information technology – the printing press.

  Plus ça change . . . The current cultural techno-malaise is born of our time spent interacting with screens. The media, both in print and online, endlessly fret about the amount of time we spend in front of screens, and the potential damage that it might cause. Everything from low-level delinquency to spree killing to autism to schizophrenia has been attributed to excessive screen time in recent years. It’s a frustrating pseudo-scientific discussion in general, as the terms of the problem are poorly delineated and ill-defined. Is five hours immersed in a video game alone of equal impact to five hours absorbing a book on a reading device? Does it matter if the game features violence or puzzles or both, or if the book is an incitement to violence or to manufacture weapons? Is watching a film at the cinema the same as playing a video game with your family?

  The data is not yet available, and studies that have been done so far have not drawn any strong conclusions or have been flawed in some way or other. Part of the discourse though is that we spend too much time on screens, when we should be doing more creative or cultural things or expressing ourselves without a reliance on technology. Of course, a paintbrush is a technological tool, as is a pencil, a sharpened stick or a particle accelerator. Very nearly nothing we do, artistic, creative or obviously scientific, could exist without technology underpinning it. Singing, dancing, even some forms of athletics and swimming, operate without direct reliance on an external technology, but as I watch my daughter tie her hair into a bun and spray it into place, clip her battered toenails and don her pointe shoes before ballet I can’t help but think how we are an animal whose entire culture and existence is completely dependent on tools.

  So, what is a tool? There are a few definitions. Here is one from a key textbook on animal behaviour:

  The external employment of an unattached or manipulable attached environmental object to alter more efficiently the form, position, or condition of another object, another organism, or the user itself, when the user holds and directly manipulates the tool during or prior to use and is responsible for the proper and effective orientation of the tool.

  Which is wordy but covers most bases.1 Some definitions make a distinction between use of a found object and a modified item, which qualifies it as technology. The key idea is that a tool is a thing external to the animal’s body that is used to exert a physical action for the animal that extends its powers.

  Tools are an inherent part of our culture. Sometimes we talk about cultural evolution in opposition to biological evolution, the former being taught and passed down socially, the latter being encoded in our DNA. But the truth is that they are intrinsically linked, and a better way to think about it is as gene-culture co-evolution. Each drives the other, and cultural transmission of ideas and skills requires a biologically encoded ability to do so. Biology enables culture, culture changes biology.

  Millions of years before the invention of the digital watch, we had an obligate technological culture. We have even specifically acknowledged our technological commitment in scientific nomenclature. One of our earliest genus cousins – probable ancestors – is named Homo habilis. Literally, this means ‘handy man’. They were a people that lived between 2.1 and 1.5 million years ago in east Africa. There are a few specimens that have been classified as habilis, which generally have flatter faces than the earlier Australopithecines from around three million years ago, but still retain long arms and small heads – their brains were typically half the size of ours. To look at, Homo habilis would have been more ape-man than man-ape. They were probably the ancestors of the more gracile Homo erectus, though co-existed with them as well, maybe indicating that Homo habilis diverged within its own species group.

  Their handy-man status is largely due to the discovery of specimens surrounded by evidence of lithic – that is, stone – technology. Some researchers suppose that the presence of tools represents the boundary between the genus Homo and what came before, meaning that humans are actually defined by tool use. The densest collections associated with Homo habilis come from the Olduvai Gorge in Tanzania, and this type of technology is referred to as the Oldowan tool set. There is a lot of technical jargon involved in describing this kit and how they were worked; ‘lithic reduction’ is one such term, which broadly means chipping a stone, often quartz, basalt or obsidian, to shape and sharpen. Many of the archaeological clues come in the form of lithic flakes – the detritus knapped from a raw stone into a tool, when the tool itself is
lost in time. Obsidian2 is an igneous rock – a type of volcanic glass, and a good choice for a cutting tool, as it forms edges so sharp that some surgeons use it today in preference to steel scalpels.

  These actions imply a cognitive ability that enables selection of suitable stones, and a plan. You need a hammerstone and a platform, an anvil, on which to chip away at the raw material. Knapping is a deliberate and skilful activity, and the set required contains different tools. Some are heavy duty, such as the Oldowan chopper, which we think was used as an axe head. Others are lighter-duty tools – scrapers for removing meat from skins, chisel-edged stones called burins and other tools for engraving wood. Again, this variation in the overall set of tools presupposes a cognitive ability to distinguish appropriate tools for different actions.

  Homo habilis is among the earliest members of the lineage that we have decided is human, and tool use is part of that definition. But this artificial boundary has not been borne out in scientific history; handy man wasn’t the first to get handy. A thousand kilometres to the north of Olduvai is Lomekwi, on the western shore of Lake Turkana, another of the key areas in the nursery of early humans. This was the site of the discovery in 1998 of a specimen that has been designated Kenyanthropus platyops, roughly meaning ‘flat-faced Kenyan man’.3 It’s a not-uncontroversial earlier great ape, that some have argued is morphologically similar enough to Australopithecus to suggest that it is not a separate species. I’m not sure it matters that much, as our taxonomic definitions are blurred at these arbitrary boundaries, and many assumptions must be made due to the specimens being few and far between – fragments from more than 300 Australopithecine individuals have been found, but only one Kenyanthropus.