Human beings arise, not from dust, but from stuff hardly more edifying: a gellid spittle. How, from this unpromising material, anything beautiful emerges – let alone anything that comprehends and communicates something of the world beyond itself – is a mystery too big to be encompassed by just one version of events. How we explain how we grow depends largely on fashion. The current fashion is to talk of rules embedded, like a code, in every cell. But this, like most shorthand explanations, fosters misunderstanding. Natalie [the author’s daughter] was not fashioned by rules. Nothing oversaw her growth. Genes set the conditions of the game, but the game itself built her; the touch and slide of surfaces, the little chemical kisses, the partings and the reunions, each part of her tissue communicating chemically with each neighbouring part as she folded herself into being. This dance, known to biology as induction, told her brain to split, squeezed her single orbit into two, and drew two little strings of brain out to the windows in her skull to make her eyes.