What is a human?

What does a human?

Rene Descartes wasn’t the first person to ponder the relationship between the human mind and the human body, but he did so more analytically than most. He concluded that the two entities were different and therefore distinct. “There is a great difference between the mind and the body, inasmuch as the body is by its very nature always divisible, while the mind is utterly indivisible,” Descartes wrote. He reasoned from his observations of himself. “When I consider the mind, or myself in so far as I am merely a thinking thing, I am unable to distinguish any parts within myself; I understand myself to be something quite single and complete.” The body was different. “There is no corporeal or extended thing that I can think of which in my thought I cannot easily divide into parts; and this very fact makes me understand that it is divisible.” Ergo: “The mind is completely different from the body.”

There was a problem with this conclusion, though. The mind might be different from the body, but no one had ever observed a mind independent of a body. Bodies were capable of existing without minds; every corpse was evidence. But not minds without bodies, at least so far as anyone knew.

There was another problem. Minds acted on bodies: I (that is, my mind) will my arm (that is, my body) to move, and my arm moves. And bodies acted on minds: My finger (body) touches a hot plate and I (mind) feel pain. How can two entities of essentially different natures act on each other?

Descartes got around this second problem by simply positing that entities of different kinds can interact. The interaction between mind and body was what gave rise to a human being.

But the first problem has never disappeared for Descartesians who insist on mind-body dualism. This group has shrunk with advances in neurology. It was one thing for Descartes to conduct thought experiments on himself while sitting in his study in Paris or Leiden; it’s another to observe different parts of an electrode-connected brain light up while the patient’s mind engages in different tasks.

Even so, the mystery remains. Moments after a person’s death, the brain can look just as it did moments before. But it’s not functioning as it did before. The mind has vanished.

Persons of religious bent can say the soul has departed the body. This doesn’t solve the problem, merely translating it into a different realm. The soul is the divine spark that animates the body—that is about to leap from God’s finger to Adam’s on Michelangelo’s fresco on the ceiling of the Sistine Chapel.

Scientists concede the principle of a spark, or rather electrical impulses that course among neurons. When the electrical impulses cease, the brain is dead—and with it, most scientists would say, the mind. 

So what does a human consist of? There might be no “I” in “team,” as coaches endlessly repeat, but there had better be an I in me. What does that I consist of?

Descartes noted that the corporeal body can be subdivided. And it can be subdivided extensively without obviously affecting the mind. I can lose a hair, a toenail, a finger, an arm, both legs—and I’m still me. I can even lose certain parts of my brain. My body is mine, but it isn’t me.

Yet if my brain shuts down, then I cease to be—at least by the standards of earthly evidence. You can poke and prod me, and I don’t react. Maybe my brain is me.

Long ago humans inferred that two parts of the body were crucial to continued life: the brain and the heart. An arrow or an ax to either could be instantly fatal. The heart was often considered the seat of emotions, as we are reminded every Valentine’s Day. The brain was the engine of thought. Some cultures practiced the eating of the hearts of vanquished enemy warriors, to absorb their courage. Eating brains was less frequent, presumably because it can lead to the transmission of brain-degenerative diseases like kuru.

Yet the brain was the more crucial of the two. People can live with weakened hearts and still be themselves. When the brain starts to go, as in dementia, the self—as it developed over decades of life—begins to go too.

Advances in understanding the electrochemistry of the brain, combined with progress in designing electrical circuits for computers, caused people to draw connections between brains and computers. In time some wondered whether the circuitry of the brain could be mimicked by the circuitry of computers, and whether it was circuitry that made humans human and might make computers human-equivalent. The jury is still out on this one.

But it raises a philosophical question worthy of Descartes. Is humanity a state of being or a functional description? Does the mind actually exist, or is it simply shorthand for sensations and behaviors? Descartes famously said, “Cogito ergo sum”–“I think therefore I am.” But was that an insight or a tautology? Is a dead human still human? The body might be the body of a human, but without doing what humans do, no one would mistake it for the living, breathing version.

Maybe its the fault of labeling. We call ourselves human beings. Maybe we should call ourselves human doings.

(In either case, we should not repeat the maxim of lavatory-stall philosophy from the 1960s: “To be is to do—Socrates. To do is to be—Sartre. Do be do be do—Sinatra.”)