We are never just ourselves.

We are ourselves plus the world we move through. A human being is not a sealed unit but a creature in constant exchange with its surroundings: light and dark, warmth and cold, soil underfoot, water, the company of others. Take the natural half of that exchange away and something in us quietly begins to fade.

We are us, plus environment. Remove the environment and we lose part of what keeps us well.

The evidence is all around us, and most of it we already feel in the body before we can name it.

The pandemic, when it shut us indoors for weeks on end, taught a whole generation a lesson their ancestors never needed to be told: that we are not built for ceilings and screens, and that twenty minutes under an open sky can do more for the spirit than an afternoon of rest on the sofa. Watch a small child near a puddle and you see the original setting restored: the delight in mud, in splashing, in rain on the skin, all of it there long before we teach them to stay clean and stay in. A single day in wild country, by the sea or under trees, can loosen something that a fortnight of comfort only tightened. Even the hospital ward bears it out: patients given a window onto trees, one well-known study found, healed faster and asked for less pain relief than those left facing a brick wall.

And we all know the homelier version of the same truth, the flat, grey mood that lifts only once we have moved, sweated, and used the body for the thing it was made to do.