How Walking Made Us Human — Part II: Why Your Best Thinking Happens on Foot

The Laetoli footprints, Tanzania — bipedal tracks pressed into volcanic ash ~3.6 million years ago, long before the brain reached its modern size. The feet came first; the brain grew up around the walking. Photo: Fidelis T. Masao et al., eLife 2016, CC BY 4.0.

"Only thoughts reached by walking have value."

Friedrich Nietzsche wrote that in 1889, and he was insufferable about it — two long walks a day, and a flat refusal to trust any idea conceived sitting down. Darwin wore a loop into the gravel of a path he called his "thinking track." Half the people you know have their own version: the problem that won't move at the desk and quietly dissolves twenty minutes into a walk.

It feels like a small trick of the mind. It isn't.

In Part I, we saw that standing up freed our hands and paid the energy bill for a bigger brain. But evolution didn't just make the brain bigger. It wired it, from the ground up, for movement — so tightly that the machinery you use to walk and the machinery you use to think turn out to be, to a startling degree, the same machinery. This is the story of what that means: for our ancestors, and for your next walk.

The brain didn't just grow. It grew to move.

When Homo erectus appeared around 1.8 million years ago, the hominin brain had roughly doubled from our Australopithecus ancestors — from about 450cc to nearly 900cc, on the way to the ~1,350cc we carry now. That jump lines up, in the fossil record, with a new way of living: covering long distances on foot, tracking game across a landscape, remembering where the water and the food would be next season.

The timing is a clue, not a coincidence. The evolutionary biologist David Raichlen and colleagues have argued that sustained endurance movement was itself a selection pressure on the brain — that an animal walking fifteen kilometres a day across shifting terrain, holding a mental map, reading the group around it, was under relentless pressure to get better at precisely the things we now call cognition. We didn't evolve big brains and then take up hiking. We became walkers, and the brain grew up around the demand.

The wiring never separated moving from thinking

Here is the part that still catches neuroscientists off guard.

The regions you'd file under "movement hardware" are the same ones doing your thinking. The basal ganglia, which sequence and automate a smooth stride, also sequence speech and switch your attention from one task to the next. The prefrontal cortex — seat of planning and self-control — lights up when you pick a line across broken ground exactly as it does when you plan an argument. Even the cerebellum, long written off as a pure motor autopilot, turns out to help with language, timing and prediction, and it expanded unusually fast in our lineage.

The cleanest evidence comes from where it breaks. In Parkinson's disease, these shared circuits degrade — and patients lose both fluent walking and executive function, together, in step. You don't get to keep one and surrender the other, because underneath they were never two systems. They were one system wearing two hats.

Why the idea comes on your usual loop — not the new trail

If walking and thinking draw on the same budget, they should trip over each other. They do — in a way that's genuinely useful to understand.

Psychologists call it dual-task interference. Ask someone to walk while counting backwards from a hundred in sevens, and two things happen at once: the arithmetic gets worse and their stride slows and wobbles. Both are dipping into the same pool of attention.

Now flip it. On a familiar route — flat, known, no decisions to make — walking asks almost nothing of you. It runs on autopilot, and that pool of attention is left wide open. That is the quiet mechanism behind Nietzsche's boast: walking doesn't supply the idea, it gets your effortful, controlling mind out of the way and lets loose, associative thought off its leash.

Which is exactly why the breakthrough tends to land on the route you've walked a hundred times — not on the spectacular new trail where you're busy not turning an ankle. If you walk to think, walk somewhere boring.

"Miracle-Gro for the brain"

The minute-to-minute story is about attention. The long-term story is chemical, and its name is BDNF — brain-derived neurotrophic factor.

BDNF keeps existing neurons alive, helps grow new ones, and strengthens the connections between them — the literal, physical substrate of learning and memory. The psychiatrist John Ratey nicknamed it "Miracle-Gro for the brain," and the label stuck because it's basically fair. A brisk walk — not a sprint, just enough to lift your heart rate — measurably raises circulating BDNF, and the hippocampus, your brain's memory-and-mapping centre, is studded with receptors for it.

Then there's the finding that belongs on a poster in every waiting room. In 2011, Kirk Erickson's team put older adults through a year of regular moderate walking. Their hippocampus didn't merely resist the shrinkage that comes with age — it grew, by around 2%, effectively winding the clock back a year or two. A part of the brain we assume only ever declines got measurably bigger. From walking.

Now the part where I ruin the party

This is a walking app's blog, so you'd expect me to tell you walking makes you a genius. It doesn't — and the fastest way to lose your trust is to pretend the evidence is stronger than it is. So here's the honest map.

Solid ground. In older adults — especially those already sliding toward mild cognitive impairment — regular aerobic walking reliably improves executive function and memory. A 2025 systematic review of randomised trials confirms the effect is real. It also, honestly, rates the overall evidence quality as moderate — promising, not ironclad.

Reasonable, less certain. In healthy younger adults, walking gives attention, processing speed and working memory a modest lift. Real, but smaller, and it swings a lot from person to person.

Oversold. Walking as a treatment for serious clinical conditions; anything promising a specific IQ bump or a shield against dementia. Those associations are interesting and worth chasing — they are not established, and the confounds are everywhere.

None of that is a letdown. Look at what survives even the strict reading: a free, side-effect-free behaviour that measurably protects the one organ we're most afraid of losing. The evidence doesn't need inflating. It's remarkable at its actual size.

One system, wearing two hats

Strip it back and the picture is simple. The body that walks and the brain that thinks did not evolve as neighbours who learned to get along. They grew from the same wiring, under the same pressure, and they still share it every time you stand up and move.

Which raises an obvious question. If walking upright rewired a primate brain this deeply, why is ours the only mind that got this particular package? Plenty of animals walk. Some even walk on two legs. In Part III, we line human walking up against everything else that moves — birds, kangaroos, our knuckle-walking cousins — and ask what, exactly, we did differently.