The nervous system

Living organisms learned very early on that the detection of changes happening in their environment was essential if they were to survive. Some photosynthetic algae had already learned how to move by wagging their flagellum, in order to look for places where lighting was optimal. The first multicellular organisms increased their chances of survival by detecting changes in their own body, and thus coordinate the response from their different cells.

Contact between one cell and its neighbors developed in the plants by means of enzyme exchange; that is, in a purely chemical way. It is a very slow process which leads to tropisms (such as the flower that turns toward the Sun, or the foliage that seeks light). But tropisms are too slow for animals; quick reactions for attack or defense are essential. A faster communication system appeared: some cells specialized in sending swift electrical impulses from one cell to another, as if along an electric wire. The nervous system began to emerge.