What if we suddenly stopped walking upright? Let's dive into a thought experiment to explore what would happen if we abandoned bipedalism.

It may be hard to believe, but the human spine wasn’t originally designed for an upright posture. Vertebrates have existed for over 500 million years, yet it wasn’t until 6 million years ago that primates first began walking on two legs — a trait exclusive to the hominin clade, of which Homo sapiens is the only surviving species. We didn’t fully adapt to bipedalism until 1.9 million years ago.

In other words, the upright spine has only been in use for a mere 0.38 percent of vertebrates' existence.

Our hominid ancestors reengineered the naturally horizontal design of the spine. They began standing upright to appear larger, to move across vast landscapes more efficiently, to gain a wider view of their surroundings, and, most importantly, to free up their hands.

As a result, our spines don’t function as they were originally designed to, even with the evolutionary adaptations we've developed, such as wider hips and stronger knees. This issue is worsened by our sedentary lifestyles, particularly our constant sitting. It’s no surprise, then, that a staggering 80 percent of adults will experience back pain at some point in their lives.

What if we reversed the process, returning our spines to their original alignment and abandoning our upright posture altogether?

Stay with us as we envision a day in a world where humans live as quadrupeds. Imagine a future where homes and public spaces are re-designed to accommodate a society that moves on all fours.

A Day in the Life of a Human Quadruped

I drift off to sleep while reading about humans who would prop themselves up with pillows and foam mattresses to ease the strain caused by their upright way of life. When I wake, I find myself refreshed, lying on the quilt-covered floor of my room.

I slip into my hand and knee pads and scurry off to the bathroom. There’s a hole in the ground with an automatic retractable cover. The process is quick and naturally suited for, ahem, relieving oneself. I skitter over to the wash basin embedded in the floor and glance at my reflection in the surrounding mirror, then sit upright as I brush my teeth, looking into a second mirror mounted lower on the wall to inspect my curved back. Which hand, knee, and foot coverings should I wear today?

My 6-year-old daughter waddles into the bathroom, walking unsteadily on two legs. “I’m a giant Homo sapiens,” she giggles, before tumbling to my side and scrambling up onto my back for a ride to the kitchen.

The refrigerator stretches low across an entire wall. Our kitchen table is a retro piece, elevated off the floor but only by about a foot (0.3 meters) to accommodate our seated posture with crossed legs.

Our house is incredibly old, modified long ago for the All Fours It movement, and is even listed on the historic homes register. When my daughter bursts into laughter, it echoes off the drop ceiling. Some owners of historic homes choose not to lower their ceilings; instead, they retain the extra height for storage, accessing it with elaborate ropes and ladders.

On Our Way to School and Work, Horizontal-style

After breakfast, my daughter and I strap on our lightweight graphene backpacks. These packs barely weigh anything. Robotic arms are built into the backpacks, acting as substitute hands when we're walking on our knuckles. Once we connect the wires from the backpacks to the brain implants at the base of our necks, the arms unfold from the sides. My daughter’s backpack is painted red with black dots to resemble a ladybug, and her robotic arms match the pattern, giving the impression of wings when they extend.

One of my backpack's hands activates the front door flap, and we rush through to the street, just in time to almost miss the school train. The train supervisor, hunched over the controls, bypasses the automatic system to reopen the door for us. My daughter leaps from the corner, grabs the rope hanging in the doorway, swings herself inside, and waves goodbye with her backpack hand. Just before the supervisor releases the handbrake, she swiftly spins in her 360-degree chair to scold a child walking upright in the aisle. The kids burst into laughter.

I rush off to the gym to strengthen my core. Despite how well our species has adapted through the ages, we still carry the vestiges of bipedal bones and muscles. Our abdominal muscles are not as strong as they should be to properly support our quadrupedal movement. Our neck bones haven't quite adjusted to support our horizontal spines, and our long thigh muscles sometimes need a massage since they are built for long strides rather than short bursts.

Some individuals depend on extra support from their backpacks — arms that extend to the ground, helping to relieve some of the weight. These models are mostly used by the elderly or those with disabilities due to ongoing debates in the medical community regarding assisted limb usage.  

One group of researchers argues that using our biological arms solely for walking leads to less brain stimulation, while another group insists that our backpack arms have seamlessly integrated into our overall body schema — after all, our brains are directing these limbs — which ensures plenty of stimulation.

My backpack buzzes, and I feel a soft pressure around my rib cage and back. It's my daughter sending me a virtual hug, and I send one back, knowing that her backpack is gently contracting in response.

I work in a customer service call center for a leading backpack provider. The hours are long, but they pass quickly. This is partly because of an implant I have for work, which shifts my focus entirely to customer interactions. I receive others' thoughts all day, blending them into automated responses shaped by an algorithm. These often involve helping customers with upgrades or reporting issues where their backpacks fail to receive data.

Another reason the hours fly by is because our chair pods rotate completely every 30 minutes – it feels like time is always moving. Some of us call our chairs 'pit roasters.' When you climb on top of the main support and secure your feet, it can feel a bit like straddling a kabob skewer. But the open cocoon that wraps around you is surprisingly beautiful. You can set it to glow, play your favorite music, or block out office noise. Studies claim it boosts productivity, satisfaction, and so on. There are even built-in bicycle pedals for exercise.

Mostly though, I think the pit roaster prevents us from staring at each other's backsides all day, which is a common pastime for quadrupeds and a major distraction.

Upright Walking, Just a Fantasy

I deactivate my work implant and receive a thought message from my daughter saying she's on her way home. When I meet her, she's bubbling with excitement over a volcanic eruption simulation she participated in today. She was close enough to the lava to feel its heat, and the class was able to measure the atmospheric levels of carbon dioxide. (Her school also has pit roasters, but with virtual reality vision.)

She's waving her arms energetically, describing a burst of pyroclastic clay, and I notice that the tread is peeling off her knuckle pads. I make a mental note, which automatically triggers an order for new pads to be shipped to us by morning.

By the time we get home, the oven has already prepared our meal — tikka masala. We close our eyes and share our favorite moments of the day, and I make sure to run the KidFilter on my thoughts to keep any adult conversations from reaching her.

Then it's time to hit the floor for sleep. We remove our backpacks, and I take a moment to appreciate the gentle curve of my daughter's back, a beauty standard often fetishized by the media — some even opting for implants to create a more exaggerated, hunched appearance.

I drift into slumber, with shadows ebbing and flowing, twisting into a vision of towering ancestors, endlessly building perches that lift them higher and higher. I am one with them, stumbling across vast stretches of land on stilts, unbalanced and perpetually leaning forward until, at last, I collapse onto the earth, feeling its pull grounding me to my place.

If the thought experiment involving quadrupeds intrigued you, be sure to check out the Stuff of Life podcast and interview with the author of "GoatMan: How I Took a Holiday from Being Human" this May. Written by Thomas Thwaites, this nonfiction book recounts Thwaites' quest to become a goat. Yes, really.