“What a piece of work is a man!” marvels Hamlet, in awe at our specialness.
How noble in reason! How infinite in faculty!
In form, in moving, how express and admirable! In action how like an angel!
In apprehension how like a god! The beauty of the world! The paragon of animals!
“The paragon of animals” is a lovely phrase. Hamlet exalts us as truly special, touching the divine, limitless in our thought. It’s a prescient phrase, too, as he raises us above other animals while acknowledging that we are one. Just over 250 years after William Shakespeare wrote those words, Charles Darwin irrefutably cemented humankind’s classification as an animal—the slightest of twigs on a single, bewildering family tree that encompasses four billion years, a lot of twists and turns, and a billion species. All of those organisms—including us—are rooted in a single origin, with a common code that underwrites our existence. The molecules of life are universally shared, the mechanisms by which we got here the same: genes, DNA, proteins, metabolism, natural selection, evolution.
Hamlet then ponders the paradox at the heart of humankind:
What is this quintessence of dust?
We are special, but we are also merely matter. We are animals, yet we behave like gods. Darwin sounds a bit like Hamlet, declaring that we have “god-like intellect,” yet we cannot deny that man— and, to bring his language into the twenty-first century, woman— carries the “indelible stamp of his lowly origin.”
This idea, that humans are special animals, is at the root of who we are. What are the faculties and actions that put us on a pedestal above our evolutionary cousins? What makes us animals, and what makes us their paragon? All organisms are necessarily unique, so that they can exist within and exploit their own unique environment. We certainly think of ourselves as pretty exceptional, but are we really more special than other animals?
Alongside Hamlet and Darwin comes a possible challenge to our ideas of human exceptionalism, from an arguably lesser piece of modern culture, the animated superhero film The Incredibles: “Everyone is special . . . which is another way of saying that no one is.”
Humans are animals. Our DNA is no different from anything that has lived in the last 4,000 million years. The coding system employed within that DNA is no different, either; the genetic code is universal as far as we know. The four coded letters that make up DNA (known as A, C, T, and G) are the same in bacteria and bonobos, orchids, oaks, bedbugs, barnacles, triceratops, Tyrannosaurus rex, eagles, egrets, yeast, slime molds, and ceps. The way they are arranged in those organisms, and how they are translated into the protein molecules that enact the functions of a living being, are all fundamentally the same, too. The fact that life is organized into discrete cells is also universal,* and these incalculably numerous cells harvest energy from the rest of the universe in a process common to all of them.
These principles are three of the four pillars of biology: universal genetics, cell theory, and chemiosmosis, which is a rather technical yet elegant word for the basic process of cellular metabolism—how cells draw energy from their surroundings, to be spent in the process of living. The fourth pillar is evolution by natural selection. Combined, these grand unifying theories coalesce to reveal something unarguable—that all life on Earth is related by common ancestry, and that includes us.
Evolution is slow, and Earth has been host to life for the vast majority of our planet’s existence. The timescales we talk about so casually in science are utterly baffling to comprehend. Even though we are a latecomer to life on Earth, our species is more than 3,000 centuries old. We have traversed that ocean of time largely unchanged. Physically, our bodies are not drastically different from Homo sapiens in Africa 200,000 years ago.* We were physically capable of speaking then as we do today, and our brains were not significantly different in size. Our genes have responded in small part to changes in the environment and diets as we migrated within and out of Africa, and genetic variants account for the minuscule percentage of DNA that spells out the differences between individuals, changes in the most superficial characteristics—skin color, hair texture, and a few others. But if you tidied up a Homo sapiens woman or man from 200,000 years ago, gave them a haircut, and dressed them in twenty-first-century clothes, they would not look out of place in any city in the world today.
There’s a conundrum in that stasis. Though we may not look different, humans did change, and profoundly. There’s debate about when this transition occurred, but by 45,000 years ago, something had happened. Many scientists think that it was a sudden change— sudden in evolutionary terms means hundreds of generations and dozens of centuries, rather than a thunderbolt. We don’t quite have the language to relate to the timescales involved in such transitions. But what we can observe from the archaeological record is that we see the emergence and accumulation of a number of behaviors that are associated with modern humans, and there was a time before that where we see fewer or none of them. Given how long life has existed on Earth, this switch happened relatively in a heartbeat.
The transformation occurred not in our bodies or physiology or even in our DNA. What changed was culture. In scientific terms, culture refers broadly to the artifacts that are associated with a particular time and place. They include things like tools, blade technology, fishing gear, and use of pigment for decorative purposes or jewelry. The archaeological remains of a hearth show the ability to control fire, to cook, and maybe its position as a social hub. From material culture, we can infer behavior. From fossils we can try to piece together what people looked like, but with archaeological evidence of the paraphernalia of our ancestors’ lives, we can address what people were like in prehistory, and when they became like that.
By 40,000 years ago, we were designing decorative jewelry and musical instruments. Symbolism in our art was rife, and we were inventing new weapons and hunting technology. Within a few millennia, we had fostered dogs into our lives—tamed wolves that accompanied our search for food long before they became our pets.
The concatenation of these behaviors is sometimes referred to as the Great Leap Forward, as we jumped into a state of intellectual sophistication that we see in ourselves today. Alternatively, it’s a “cognitive revolution,” but I dislike the use of that phrase to describe a process that was both continuous and probably lasted a few thousand years or more—real revolutions should be thunderbolts. Nevertheless, modern behavior emerges permanently and quickly in several locations around the world. We began to carve complex figurines, both realistic and abstract, sculpted make-believe chimeras out of ivory, and we adorned cave walls with pictures of hunts and of animals important to our lives. One of the two earliest known pieces of figurative art by Homo sapiens that we know of is a 40,000-year-old twelve-inch statue of a lean man with the head of a lion. It was carved from a mammoth tusk during the last Ice Age.
Soon after that time we were making small statues of women. They are known today as Venus figurines. We don’t know if there was a specific purpose to these dolls, though some researchers think they may have been fertility amulets, as their sexual anatomy is exaggerated: bosomy women with swollen labia, and often bizarrely small heads. Maybe they were just art for art’s sake, or toys. Either way, to create such sculptures requires great skill and foresight, and a capacity for abstract thought. A lion-man is an imagined being. The Venus amulets are deliberate misrepresentations, abstractions of human bodies. These figures cannot exist in isolation, either; artisan craft requires practice, and though today only a handful of these beautiful works of art remain, they must represent an iterative process, a lineage of skilled craftspeople.
Some of these types of traits pop up before the full transition to our modern behavior, but they do so fleetingly, and then vanish from the archaeological record. Homo sapiens were not the only humans to have existed in the last 200,000 years, and not the only ones to have refined culture. Homo neanderthalensis, far from the brutes of popular lore, were simply people, too. We are wrong to think of them as merely upright apes, living in dust with crude language and tools, all set for extinction. Neanderthals showed clear signs of modern behavior: They made jewelry, employed complex hunting techniques, used tools, had a control of fire, and made abstract art. We have to consider that they also were sophisticated in a way indistinguishable from our direct
Homo sapiens ancestors, which undermines the uniqueness of our own forward leap. Though we have traditionally considered Neanderthals to be cousins to us, they were also ancestors: We now know that our lineage and theirs diverged more than half a million years ago, and both groups were isolated in time and space for almost all of that period. But our ancestors left Africa some 80,000 years ago, and were immigrants into Neanderthal territory.
We reached Europe and central Asia, and around 50,000 years ago, we bred with them. Their bodies were different enough that they lie outside the range of human physical diversity as we see it today—a bit less chin, a bit more chest, heavy-set brows, and robust faces. They weren’t so different that we didn’t have sex with them, women and men from both sides of the species fence, and together we had children. We know this because our genes are in their bones, and theirs are in our living cells. Most people of European descent carry a small but significant percentage of DNA that was acquired from Neanderthals, and this blurs any hope of a clear boundary between two sets of people that we have declared separate species—that is, organisms that cannot produce fertile offspring. Though Neanderthal DNA is slowly being purged from our genomes for reasons that are not fully understood, humans today bear their living genetic heritage, as we do the genes of another type of human, the Denisovans, farther to the east, and maybe others that are yet to be discovered but whose legacy sits within our DNA.
When we first met, the Neanderthals and those other people were not long for this world, and by around 40,000 years ago, Homo sapiens had outlived the last of them. Whether the Neanderthals had undergone a full transition to the behavioral modernity as we saw in Homo sapiens, we do not know, and may never know, but the evidence is pointing toward those cavemen and women being much like ourselves in every way.
We lived and they died. We don’t know what gave Homo sapiens the edge over Neanderthals. All life is set for extinction over a long enough timescale; more than 97 percent of species that have ever existed are already gone. The Neanderthals’ tenure on Earth was much longer than we have racked up so far, and we are yet to firmly understand why their light was finally snuffed out 40,000 years ago. We don’t think there were ever very many Neanderthals, which may have contributed to their demise. Maybe we outsmarted them. Maybe we brought with us diseases that we had lived with and earned immunity to, but which were lethal to a virgin population. Maybe they simply petered out of existence. What we do know though is that around this time, the last type of human began to permanently and globally show signs of who we are today.
We certainly outbred all our nearest relatives. Homo sapiens went forth and multiplied very effectively. We’re the dominant life form on Earth by many measures, if ranking matters to you (though bacteria outnumber us—you carry more bacterial cells than human ones—and are far more successful in terms of longevity. They have a four-billion-year lead on us, and no prospect of extinction). Today there are upwards of seven billion humans alive, more than at any time in history, and that number is still rising. Through our ingenuity, science, and culture, we have eradicated many diseases, drastically reduced infant mortality, and extended lifespan by decades.
Hamlet marvels at our brilliance, as have scientists, philosophers, and religions for millennia. But the progress of knowledge has chipped away at our specialness. Nicolaus Copernicus dragged us away from a world at the center of the universe to one merely orbiting an ordinary star. Twentieth-century astrophysics revealed our solar system as an average one among billions in our galaxy, which itself is one of billions in the universe. We still only know of one world that harbors life, but since 1997, when the first planets beyond our Sun’s gravity were discovered, we have learned of thousands in the heavenly firmament, and in April 2018 a new satellite was launched specifically to seek out strange new worlds. We’re getting a good grip on the conditions required for chemistry to transition into biology, and for life to emerge from a sterile rock. The question of whether there is life beyond Earth has mutated: It would now be surprising if there weren’t living things elsewhere in the
universe. That is all still to come, and for now, we only know of life on Earth. But we might not be as unique as we once thought, and the more we learn the clearer that becomes.
On Earth, Charles Darwin began the process of inching us back into the natural world, and away from special creation. He showed that we are animals, evolved from other animals, and placed us firmly as a creature begotten not created. All of the incontrovertible molecular evidence of those pillars of biology was yet to come when he exposed the world to his big idea in 1859 in On the Origin of Species. He avoided including humans in that great work, but teased us that his mechanism of natural selection would soon shed light upon our own origins. In The Descent of Man in 1871, he applied his meticulous and foresightful brain to our genesis, and cast us as an animal evolved just like every organism in Earth’s history. Mostly bald, you’re an ape, descended from apes, your features and actions carved or winnowed by natural selection.
In that sense we are not special. We evolved with a biology indistinct from all life, and under the auspices of a mechanism that is similarly universal. But evolution also equipped us with a suite of cognitive powers that gave us, ironically, a sense of separateness from nature, because it allowed us to develop and refine our culture to a level of complexity well beyond any other species. It gave us a clear sense that we are special, and specially created.
Yet many of the things once thought to be uniquely human are not. We have extended our reach so far beyond our grasp by utilizing nature and inventing technology. But many animals also use tools. We have decoupled sex from reproduction, and almost always have sex for fun. Scientists are reluctant to admit the possibility of pleasure in animals, but even so, a huge proportion of sexual activity in animals does not and cannot result in reproduction. We are frequently a homosexual species. Once—and in many places to this day—homosexuality was decried as contra naturam, a crime against nature. In fact, sexual acts between members of the same sex abound in nature, in thousands of animals, and, for example, may well dominate male giraffe sexual encounters.
Our ability to communicate appears to trump all other animals, though maybe we just don’t know what they’re saying yet. I am writing this book and you are reading it, which is a degree of communication that has evolved far beyond any other level we have observed in any other species. Though that certainly makes us different, a mantis shrimp doesn’t give two hoots about that. It can see in sixteen different wavelengths of light compared to our puny three,* which is rather more useful to them than all the culture and self-regard that we have mustered over the millennia.
Nevertheless, a book is a thing that typifies the gap between us and all other beasts. It is the sharing of information generated by thousands of others, almost none of whom I am closely related to. I have studied their ideas and recorded them into a tool of almost unimaginable complexity, so that our minds might be enriched with this collection of stories that are new and hopefully interesting to anyone who cares to pick it up.
This is a book about the paradox of how we became us. It is an exploration of an evolution that bestowed enormous powers of intellect on an otherwise average ape, to create tools, art, music, science, and engineering. Through old bones and, nowadays, genetics, we know about the mechanics of our evolutionary journey through the eons (though there is so much still to discover), but we know far less about the development of our behavior, of our minds, and of the way that we uniquely evolved into the cultural and social beings that we are today.
At the same time, though, it is a book about animals, of which we are one. We’re a self-centered species, and we find it hard not to see ourselves and our behaviors 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 behavior 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 behavior, of creating horrible nightmares—violence, warfare, genocide, murder, rape. Are these different from the often horrifying behaviors 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 scrutinizing the reasons behind the evolution of behavioral 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 behaviors are outliers, truly unusual characteristics. Others might be generalizable 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 behaviors 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 behavior today with a presumption that that is why the behavior emerged in the first place. There are many tempting myths about the origin of our bodies and behaviors 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 behaviors are explained with the central idea of evolution, which is adaptation. Many behaviors, 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 behaviors, which we will inspect in detail. We see familiar sexual behaviors 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 toward them, you can see things that wish to eat you and swim away. Once it had evolved, vision spread rapidly. Since then, the genetic program 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 behaviors 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 socialized 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 case:
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. Here is a compendium of what unequivocally fixes us within the animal kingdom, and simultaneously reveals how we—humanimals—are extraordinary.