Then, around two and a half billion years ago, there was enough oxygen waste in the atmosphere that a scavenger ancestor emerged to make use of it. It learned to gulp in all that leftover oxygen and excrete carbon dioxide: the first cycle of aerobic life.
Oxygen, it turned out, produced 16 times more energy than carbon dioxide. Aerobic life forms used this boost to evolve, to leave the sludge-covered rocks behind and grow larger and more complex. They crawled up to land, dove deep into the sea, and flew into the air. They became plants, trees, birds, bees, and the earliest mammals.
Mammals grew noses to warm and purify the air, throats to guide air into lungs, and a network of sacs that would remove oxygen from the atmosphere and transfer it into the blood. The aerobic cells that once clung to swampy rocks so many eons ago now made up the tissues in mammalian bodies. These cells took oxygen from our blood and returned carbon dioxide, which traveled back through the veins, through the lungs, and into the atmosphere: the process of breathing.
The ability to breathe so efficiently in a wide variety of ways—consciously and unconsciously; fast, slow, and not at all—allowed our mammal ancestors to catch prey, escape predators, and adapt to different environments.
It was all going so well until about 1.5 million years ago, when the pathways through which we took in and exhaled air began to shift and fissure. It was a shift that, much later in history, would affect the breathing of every person on Earth.
I’d been feeling these cracks for much of my life, and chances are you have, too: stuffy noses, snoring, some degree of wheezing, asthma, allergies, and the rest. I’d always thought they were a normal part of being human. Nearly everyone I knew suffered from one problem or another.
But I came to learn that these problems didn’t randomly develop. Something caused them. And the answers could be found in a common and homely human trait.
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A few months before the Stanford experiment, I flew to Philadelphia to visit Dr. Marianna Evans, an orthodontist and dental researcher who’d spent the last several years looking into the mouths of human skulls, both ancient and modern. We were standing in the basement of the University of Pennsylvania Museum of Archaeology and Anthropology, surrounded by several hundred specimens. Each was engraved with letters and numbers and stamped with its “race”: Bedouin, Copt, Arab of Egypt, Negro Born in Africa. There were Brazilian prostitutes, Arab slaves, and Persian prisoners. The most famous specimen, I was told, came from an Irish prisoner who’d been hanged in 1824 for killing and eating fellow convicts.
The skulls ranged from 200 to thousands of years old. They were part of the Morton Collection, named after a racist scientist named Samuel Morton, who, starting in the 1830s, collected skeletons in a failed attempt to prove the superiority of the Caucasian race. The only positive outcome of Morton’s work is the skulls he spent two decades gathering, which now provide a snapshot of how people used to look and breathe.
Where Morton claimed to see inferior races and genetic “degradation,” Evans discovered something close to perfection. To demonstrate what she meant, she walked over to a cabinet and retrieved a skull marked Parsee, for Persian, from behind the protective glass. She wiped bone dust on the sleeve of her cashmere sweater and ran a neatly trimmed fingernail along its jaw and face.
“These are twice as large as they are today,” she said in a staccato Ukrainian accent. She was pointing at the nasal apertures, the two holes in the back of the throat that connect to the nasal passages. She turned the skull around so it was staring at us. “So wide and pronounced,” she said approvingly.
Evans and her colleague Dr. Kevin Boyd, a Chicago-based pediatric dentist, have spent the last four years X-raying more than 100 skulls from the Morton Collection and measuring the angles from the top of the ear to the nose and from the forehead to the chin. These measurements, which are called the Frankfort plane and N-perpendicular, show the symmetry of each specimen, how well-proportioned the mouth was relative to the face, the nose to the palate, and, to a large extent, how well the people who owned these skulls might have breathed.
Every one of the ancient skulls was identical to the Parsee sample. They all had enormous forward-facing jaws. They had expansive sinus cavities and broad mouths. And, bizarrely, even though none of the ancient people ever flossed, or brushed, or saw a dentist, they all had straight teeth.
The forward facial growth and large mouths also created wider airways. These people very likely never snored or had sleep apnea or sinusitis or many other chronic respiratory problems that affect modern populations. They did not because they could not. Their skulls were far too large, and their airways too wide for anything to block them. They breathed easy. Nearly all ancient humans shared this forward structure—not just in the Morton Collection, but everywhere around the world. This remained true from the time when Homo sapiens first appeared, some 300,000 years ago, to just a few hundred years ago.
Evans and Boyd then compared the ancient skulls to the modern skulls of their own patients and others. Every modern skull had the opposite growth pattern, meaning the angles of the Frankfort plane and N-perpendicular were reversed: chins had recessed behind foreheads, jaws were slumped back, sinuses shrunken. All the modern skulls showed some degree of crooked teeth.
Of the 5,400 different species of mammals on the planet, humans are now the only ones to routinely have misaligned jaws, overbites, underbites, and snaggled teeth, a condition formally called malocclusion.
To Evans, this raised a fundamental question: “Why would we evolve to make ourselves sick?” she asked. She put the Parsee skull back in the cabinet and took out another labeled Saccard. Its perfect facial form was a mirror image of the others. “That’s what we’re trying to find out,” she said.
Evolution doesn’t always mean progress, Evans told me. It means change. And life can change for better or worse. Today, the human body is changing in ways that have nothing to do with the “survival of the fittest.” Instead, we’re adopting and passing down traits that are detrimental to our health. This concept, called dysevolution, was made popular by Harvard biologist Daniel Lieberman, and it explains why our backs ache, feet hurt, and bones are growing more brittle. Dysevolution also helps explain why we’re breathing so poorly.
To understand how this all happened, and why, Evans told me, we need to go back in time. Way back. To before Homo sapiens were even sapiens.
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• • •
What strange creatures. Standing in the tall grass of the savanna, all gangly arms and pointy elbows, gazing out into the wide, wild world from foreheads that looked like hairy visors. As the breeze swayed the grass, our nostrils, the size of gum drops, flexed vertically above our chinless mouths, picking up whatever scents the wind brought in.
The time was 1.7 million years ago, and the first human ancestor, Homo habilis, was roaming the eastern shores of Africa. We’d long since left the trees, learned to walk on our legs, and trained ourselves to use the small “finger” on the inside of our hands, to turn it upside down into an opposable thumb. We used this thumb and fingers to grab things, to pull plants and roots and grasses from the ground, and to build hunting tools from stone that were sharp enough to carve tongues out of antelope and strip meat from bone.