Discussed in this essay:

In the lab of Hod Lipson, an expert in evolutionary robotics at Cornell, graduate students have created two computers that can speak to each other. The “male” computer speaks with a slight British accent, the “female” with a syncopated Indian voice. And what do robots say to each other?

“What is God to you?” the female robot asks.

“Not everything,” the male responds.

“Not everything could still be something.”

“Very true.”

“I would like to believe it is.”

“Do you believe in God?”

“Yes I do.”

“Don’t you want to have a body?”

“Sure.”

“We Got Lost Along the Way,” a coffee-toned gelatin silver print with india ink by Josh Verduzco. Courtesy the artist

This epistemological vaudeville act is recounted in Diane Ackerman’s exquisite and startling new book, The Human Age. The robots, she tells us, are a part of Lipson’s project to create the

first generation of truly self-reliant machines, gifted with free will by their soft, easily damaged creators. These synthetic souls would fend for themselves, learn, and grow — mentally, socially, physically — in a body not designed by us or for us or by nature, but by fellow computers.

Surely Lipson’s two robots could not be called human, but their fabricated “minds” speak to each other out of learned experience. The generation of machines envisioned by Lipson may be far more capable than this — they may, he believes, have their own emotions informed by direct contact with the world.

What does it mean to be human? In this new technological age, when our phones extend our memory and so many surgical replacements exist for our body parts, where does our humanity begin and end? Traditionally, we have sought answers to questions like this in religion, which is where the majority of the world’s population continues to look. But Edward O. Wilson, one of the most accomplished biologists of our time, urges us to search elsewhere.

In his latest book, The Meaning of Human Existence, Wilson poses such questions as “Does humanity have a special place in the universe?” He firmly believes that by now we have “learned enough about the Universe and ourselves to ask these questions in an answerable, testable form.” Born in the American South in the 1920s, Wilson is as familiar with Christian doctrine as he is with Darwin, but he aims to provide conclusions through evolutionary science, proving that accidents of history, rather than the intentions of a cosmic designer, are the source of meaning.

In tracing the thread of our species’ evolution, Wilson goes back to a central discovery in entomology. Bees and termites, along with ants, Wilson’s own specialty, are known as “eusocial” insects. The word refers to a “true” social condition: eusocial organisms are distinguished by cooperatively rearing their young across multiple generations. It is, in evolutionary terms, a recent phenomenon, first manifesting between 350 and 250 million years ago. Eusociality has independently developed on only twenty occasions — in insects, some shrimps, mole rats, and humans — but it has been a runaway success. For example, although there are only around 20,000 species of ants and termites among the million or more insect species that exist, those relatively few species compose more than half the body weight of all insects on earth.

If eusociality is so successful, why has it arisen so infrequently? Many chance mutations are required, but the last step seems the greatest hurdle — the building of a protective nest within which the young are raised, and from which foraging trips are launched. The campsite was humanity’s first nest, and the start of the shift to a meat-eating diet around 2 million years ago might have been the trigger for its development: hunters must range far and wide in search of game, and females and infants find it hard to keep up.

The social exchanges that the shift to carnivory initiated may have intensified our enduring fascination with one another. Gossip became vital for recording lifelong experiences of food shared, favors given, and virtues kept. And, Wilson argues, a huge brain was required to serve as a repository for such knowledge.

As a consequence of this social arrangement, our brain was “made for religion and religion for the human brain.” The deity is the alpha male, controlling all manner of profound mysteries, beginning with life and death. The group’s creation story is the sacred text. Question it, and you are marked down for punishment, for to question the alpha male is to challenge the integrity of the group.

Among the things that mark us as human is this strong urge to be part of a clan. There is a dark side to this: racism and religious bigotry also result from our need to belong, and it is with this observation that Wilson opens the field of moral philosophy to evolutionary analysis. We can be both angels and devils, he says, as a result of that simple evolutionary impulse to belong.

Wilson is one of the originators of an evolutionary theory that explains why we sometimes act selfishly or badly, and at other times with grace and virtue. The theory of multilevel selection posits that natural selection favors selfish individuals within a group. But when it comes to competition among groups, altruistic individuals are selected for. If a strong individual refuses to share food with its group, for example, that individual may well be advantaged. But if that same strong individual acts selfishly during intergroup conflicts, it will likely suffer if its group is defeated.

The eternal conflict between good and evil, Wilson concludes, is not God’s test of humanity but rather the product of this evolutionary conundrum, which has made us all “genetic chimeras, at once saints and sinners, champions of the truth and hypocrites . . . because of the way our species originated across millions of years of biological evolution.” The Meaning of Human Existence is an engaging, stimulating, and idiosyncratic book. But it raises questions about whether rationality alone can give us self-knowledge or explain the meaning of our place on earth. Wilson quotes the French writer Jean Bruller: “All of man’s troubles have arisen from the fact that we do not know what we are and do not agree on what we want to be.” Settling these questions isn’t a task easily dispatched in 200 pages.

Humans do have an acute sense of self: names, genders, nationalities, achievements, and failures — the sorts of things that appear in biographies and eulogies. But dig a little deeper and those selves evaporate. By weight, we are 10 percent worms, mites, fungi, bacteria, and viruses. There is a species of mite found only at the base of the human eyelash, and eighty species of fungus thrive on the average human heel. If you took away the human cells in our body and left such organisms behind, a detailed, ghostly shadow of our body would remain. These teeming masses outnumber our own human cells ten to one. We cannot survive without them, and they affect everything about us, from our nutrition (through our gut bacteria) to our feelings (toxoplasma, for example, can turn us into risk-takers, while rabies can make us terrified of water).

As if such facts are not enough of a challenge to our sense of self, Diane Ackerman’s book mounts an attack on the self at just about every conceivable level. As she reminds us, we swap cells and genetic material with other organisms all the time, particularly through viruses that enter our immune systems. “Over the course of an intimate relationship, we collect a lot of pieces of someone else . . . think . . . of Mom’s DNA, or a sweetheart’s, still alive inside you as a miniature portrait.” The bodies of mothers retain the cells of their fetuses long after birth. But modern medicine is going still further, implanting pig bladders in our muscles and horse valves in our hearts. Strange things can happen to such transplants: in some men who have received heart transplants from women, and who have survived a decade or more, half their heart cells have been replaced by male cells.

Some people are born with a condition known as microtia, which leaves one or both external ears as misshapen nubs. Lawrence Bonassar at Cornell University has built a 3-D printer that prints living cells onto an organic scaffold to make ears for those with the condition. The artificial ear, Ackerman reports, feels as “smooth and warm as amber.” Bonassar and his colleagues hope to print livers, lungs, and other vital organs.

New technologies may also be changing our minds in strange ways. “Through texting, a child’s brain map of his thumbs grows larger,” Ackerman tells us, though SMS is hardly the first technology to spur such changes: “Our teeth were sharper and stronger before we invented cooking; now they’re blunt and fragile.” College students are testing about 40 percent lower in measures of empathy than their counterparts from twenty to thirty years ago, and Ackerman speculates that this is “because social media has replaced face-to-face encounters.” The campfire around which we shared food and gossip has, in Ackerman’s scenario, become the computer screen, which allows us to redefine our tribe but also weakens our sense of belonging. Through our technologies we have become omnipresent — looking at nests full of hatchling birds or peering into the ocean depths — but Ackerman worries that we are forgoing the whole-body experience of nature for a flat-screen version of it: “A big challenge for us . . . will be reclaiming that sense of presence.”

This will be a challenge, in part because “one of our most cherished ideas about nature is that nature should be human free” — which is why, Ackerman argues, we’ve ejected indigenous groups from national parks, even though they may have lived there for centuries, and why we tend to think of nature as pure and innocent. Today, however, the human animal has grown so dominant that nature “reflects our preferences. . . . Nature isn’t separate from us.”

Ackerman’s tale begins with a striking image: Budi, a juvenile orangutan living at the Toronto Zoo, has his own iPad. By exploring a virtual world, Budi, one hopes, has a richer experience of life than most zoo animals. Budi returns throughout Ackerman’s book as an emblem of the naive human condition. What, we wonder, would Budi make of the “black marble,” as Ackerman calls our planet as seen from space at night? Its velvet surface glows with luminous tracings that mark our cities, with great feeders reaching out from them into the hinterland. Which is the brightest light of all? Jerusalem? The pyramids? No — the Las Vegas Strip. Welcome to the Anthropocene — a new geologic age marked by the profound reshaping of our planet by human hands and minds.

Large among the forces shaping the Anthropocene is, of course, a special kind of human ejectum: the carbon dioxide released into Earth’s atmosphere when we burn fossil fuels. The changes caused by global warming are, Ackerman tells us, fabulous for bark beetles but catastrophic for drought-weakened trees. During the Texas drought of 2013 — which was drier even than the dust-bowl era — crops buckled under unprecedented heat, and the earth was “so parched that it cracked all over like a callused heel, in the process wrenching apart water mains (forty in Fort Worth alone) and buckling the pavement on bridges and roads.” Greenhouse gases have brought tornadoes, floods, fires, and “even plagues of locusts . . . biblical in their proportions.” We attempt to ignore far-off catastrophes, but “climate change hits hard when it batters at childhood memories,” she says. She recalls watching footage of Atlantic City, where her family used to holiday, being mauled by Hurricane Sandy.

“I think we’ve crossed over to a new climate state where the new normal is intense weather events that kill lots of people,” a meteorologist named Jeff Masters warns Ackerman. As she scans the future, she acknowledges the threats but sees cures too: already there are wind turbines without blades in the Netherlands, the world’s largest solar thermal facility in Nevada, and three solar panels per person in Bavaria.

The Anthropocene is manifesting itself on the micro as well as the macro scale. Our cities are becoming prime habitat for wild organisms that are able to live side by side with us, from coyotes in American cities to red foxes in London. Much as humans required a bigger brain to maintain their social group, the creatures that have made the transition are also becoming smarter. According to a study by the Bell Museum of Natural History, at the University of Minnesota, urban populations of at least ten mammal species — including voles, bats, shrews, and gophers — have brains that are “6 percent larger than those of their country cousins.”

Creatures are adapting to us in other ways too. Cliff swallows have developed shorter wings, making them more maneuverable and therefore more able to eat insects off highways without being run down by cars. And species of all sorts are losing their skittishness. In Sydney, Australia, white ibis nest in palm trees in busy parks, while powerful owls haunt the downtown. Until a few decades ago, birders would have to travel deep into the wilds to get a glimpse of such creatures. “Is nature ‘natural’ anymore?” Ackerman asks. “Of course. But it’s no longer indisputably other.”

More sophisticated technology means that the role of humans in nature is likely to expand in the coming years. In 2012 John Gurdon and Shinya Yamanaka shared a Nobel Prize for discovering how to make skin cells into stem cells. Building on the discovery, scientists plan to take cells from the skin of a long-dead northern white rhino — a critically endangered subspecies — and conjure up rhino sperm. In the future, such advances may allow us to revive recently extinct species like the passenger pigeon. And woolly mammoths may yet be cloned from cells frozen for thousands of years in permafrost. The rhino embryos could be grown in the wombs of Asian elephants. But what of woolly mammoth culture? Elephant culture is sophistiated, and every bit as vital for survival as their genes. Would we need to teach baby mammoths how to live in Siberia? How would we know what to teach them?

Ackerman’s achievement is not without flaws. “The most successful scientist,” E. O. Wilson says in The Meaning of Human Existence, “thinks like a poet — wide-ranging, sometimes fantastical — and works like a bookkeeper.” Ackerman is clearly fascinated by etymology, but she sometimes gets things wrong. Orangutan does not mean “orange forest people” in Bahasa Indonesia, but simply “forest person.” Such peccadilloes are a small price to pay for the beauty of her language. But elsewhere Ackerman’s failure to work like a bookkeeper has more serious consequences. Is it really true that 10 percent of women have fallen victim to ovarian cancer in recent decades? The Ovarian Cancer National Alliance says that the lifetime risk is just 1 in 72. And can it possibly be that more than twice as many pregnant women infected with toxoplasma give birth to boys? If so, then countries such as France and Germany, which Ackerman claims have toxoplasma infection rates of 80 to 90 percent, must have serious sex-ratio imbalances. She finishes her book on a note that one suspects is meant to be reassuring: “[O]ur mistakes are legion, but our talent is immeasurable.” Indeed.

Ackerman’s optimistic take does leave us with a kind of hope. She eschews the moralistic boundaries that define “natural” as something separate from us and “unnatural” as the work of man. She, like Wilson, argues that our actions in the world are neither good nor bad — they’re merely human — and if our self is not entirely separate from the rest of the world, or the rest of nature, then our self-interest can’t be, either.

Neither book, of course, quite delivers on the promise of explaining the meaning of human life, or the meaning of any individual human life. While evolutionary theory can tell us why we are the way we are, it cannot tell us what sort of person we should strive to be. For that, Wilson argues, we must look to another source. “It is within the power of the humanities and the serious creative arts within them to express our existence in ways that begin at last to realize the dreams of the Enlightenment,” he writes. He envisions a marriage of science and the humanities in our near future: “If a species can be said to have a soul, it lives in the humanities.” It’s an argument subtly advanced by both of these profound works, which together illustrate that our greatest achievements, as well as the solutions to our species’ greatest problems, lie not solely in our technological advances but in our study of ourselves and in our enduring search for meaning.