India, Oct. 2 -- Every living thing, from the simplest cell to the human brain, exists only by virtue of its ability to register and respond to the world beyond its boundaries. Life began, quite literally, at the interface between inside and outside - at the thin membrane that separated the organism from its surroundings yet kept it in constant conversation with them. Through that boundary flowed everything that mattered: energy, information, and the signals of threat or nourishment.

Consciousness is not a thing that life has but the way life listens. The single-celled amoeba senses gradients of light and sugar, a worm feels vibration and adjusts its motion; a bird detects magnetic fields as guidance; and we, at the summit of this sensit...