Human: The Science Behind What Makes Us Unique
Michael S. Gazzaniga
Ecco, July 2008
450 pages, $27.50
In 1945, anthropologist George Murdock published a list of traits that all human societies supposedly share, from the most urbanized Tokyo neighborhood to the leakiest mud-hut village in the Amazon. Murdock’s sixty-seven “cultural universals” included obvious ones like marriage, cooking, and law but also surprising or overlooked universals like puberty initiation, divination, jokes, and incest taboos. The list, of course, came out as World War II ended and if it hadn’t caused so much contention among scholars, it might have been a wonderful chance to reflect on what binds humans together.
Compiling human universals has become a favorite scientific pursuit since then, though most scientists today take a tack other than anthropology. In his new book, Human, Michael Gazzaniga employs evolutionary biology with the goal of explaining how all of those sixty-seven universals (and lots more) could have evolved, and why they might have given our ancestors advantages in the jungle. The result is dizzying. Is it true that gossip or social lying makes us human—and if so, should we be depressed by that? Or is it play that makes us human? Or language? Or art? Or are all of those just byproducts of our elephantine brains, which arose for different purposes entirely, like organizing mammoth hunts?
Talking about human evolution raises the question of what we evolved from. An army of biologists has proven that pretty much every “uniquely human” trait has an antecedent, however dim, in some rat or pig or parrot. Gazzaniga’s book, helped along by his corny asides, explains dozens of such studies. Most involve trying to deceive some poor chimp or child to glimpse how their minds work. A typical experiment involves putting a toy under a handkerchief to see if a baby cries when it “disappears,” which tests the notion of “object permanence.”
But however they vary in particulars, all the studies address one overarching question: Are human beings special? We’re different from other species, obviously (though Darwin mostly disagreed). But different in kind or degree? Gazzaniga has a clever answer. After noting all the ways that animal behavior mirrors our own, he can’t quite claim that humans are wholly different. But he uses the metaphor of a “phase shift” to explain how traits found in many common species can still add up to a human being:
A foggy mist is made up of the same stuff as an iceberg. In a complex relationship with the environment, the same substances with the same chemical structures can become quite different in their reality and form. Indeed, I have decided that something like a phase shift has occurred in becoming human ... [W]hile we can use lathes to mill fine jewelry, and chimpanzees can use stones to crack open nuts, the differences are light-years apart. And while the family dog may appear empathetic, no pet understands the difference between sorrow and pity.
Because Gazzaniga is a brain guy (he directs the center on neuroscience at the University of California at Santa Barbara), the human brain dominates this book. Every topic—arts, morality, bipedalism, whether a chimpanzee would make “a good date”—eventually wends back to brain architecture and function. Sometimes he focuses on neuroanatomy. Other times, he’s philosophical: The last chapter speculates on how robotics and artificial intelligence may cleave the essence of the human mind from its fleshy body. Usually, he combines the two approaches, and he makes a detailed case for the difference between our brains and animals.’ The difference is not, as commonly thought, our outstanding brain-mass-to-body-mass ratio (though that’s important). Really, Gazzaniga says, it’s the unique way our common mammalian neurons are wired together that sets us apart—another phase shift. For example, humans have internal feedback loops among neurons that allow us to ruminate and that probably play a role in self-consciousness. We have special “mirror neurons” as well that fire not only when we do something like frown, but also when we merely observe another person frowning, a process that allows us to understand other people’s states of mind and empathize.
Ah ha! So wiring makes us human? Maybe. Except that some animals have mirror neurons, whereas autistic people—who surely are human—probably have deficient mirror neuron systems. Plus, the exact wiring diagram depends on the environment the brain was raised in—child abuse victims, among others, end up with differently structured brains. And the brain’s pretty plastic anyway, so it can rewire itself to some extent. And really, what might be crucial isn’t our brain’s connectivity but its disconnections: Our left and right hemispheres, once redundantly identical, now work independently. That cranial division of labor allowed the hemispheres to specialize and adopt new “modules” for new tasks like language or recognizing faces, which affects the wiring ... and we’re right back where we started.
Well then, maybe emotions make us human—especially because emotions prop up, or even dominate, another human specialty, logical reasoning. In contrast to chimp and child studies, some neurologists study people with localized brain damage, especially when that damage warps their personalities. People with damage to emotion centers, Gazzaniga reports, can reason just fine and come up with a number of solutions to life’s typical problems. But, lacking happiness or fear, they cannot attach a value to possible solutions, rendering them incapable of figuring out which is best. All their logic goes for naught.
The effect of emotions also comes up when Gazzaniga delves into moral reasoning, our ability to decide what’s ethically good or bad. Under the surface here is an interesting political drama that Gazzaniga never brings up, but that must have informed his own feelings. Gazzaniga serves on the President’s Council on Bioethics, the council President George W. Bush started in 2001 to advise his administration on stem cells and cloning therapies. The committee famously (some say notoriously) mirrored Bush’s belief that such research was immoral. Its intellectual justification was rooted in what Dr. Leon Kass, former chair of the council, described as the “wisdom of repugnance”—the belief that the deep, automatic disgust some people feel when contemplating certain procedures should guide our conscious decisions about whether to ban them.
Gazzaniga has no doubt that the emotion of disgust is deep seated. But he questions how wise disgust is. He argues that disgust (which is unique to humans) arose from a natural tendency to shun our own bodily waste and dead relatives, which cuts down on disease transmission. That’s good. But at some ill-defined point in our past, “disgust became more generalized to include aspects of appearance, bodily functions, and some activities,” he says. In other words, disgust crept into places it might not belong, including religious and social rituals such as the Hindu caste system and the insistence of monarchies on keeping bloodlines pure. Altogether, this argues that repugnance lacks the wisdom Kass implied. It’s hardly surprising that Gazzaniga dissented strongly from the majority of the President’s council on many decisions, once writing in an official report, “I disagree with most of the moral reasoning argued in this report. For me it is full of unsubstantiated psychological speculations on the nature of sexual life and theories of moral agency.”
Gazzaniga’s reasoning is less strong about the origins of other human traits. For example, did mellifluous, complex human language really develop to help primate males persuade primate females to mate with them? Wouldn’t that leave women mute? No, he says, because women stereotypically talk more later in relationships to convince men to stick around and rear children. In such cases, Gazzaniga’s explanations, or at least the explanations of other scientists he cites, teeter on becoming fabulous (as in “fable-like”) just-so stories.
It’s a mug’s game to try to unravel what in the mind evolved when and why—the brain is the ultimate Gordian knot, and you can concoct dozens of plausible stories to explain the origins of almost any aspect. In the end, what makes humans special is that we combine all the brain modes and mind modules catalogued in Human. If you approach Gazzaniga’s book hoping to find the essence of humanity, you’re going to get a headache. But if you read expecting a little less, and let yourself be swept away in all the ways that human beings are special, you’ll walk away awed. Call it a phase shift in expectations.
Sam Kean is the associate editor of Search.
