We tend to associate consciousness and intelligence with the appearance of wilfulness or intentionality – that is, decision-making that results in a particular behavioural outcome. Whether or not humans have free will, we take actions that seem wilful: she finished her coffee, whereas her friend left her cup half full. Fungi express simpler versions of individualistic behaviour all the time. Patterns of branch formation are a good example of their seemingly idiosyncratic nature. Every young fungal colony assumes a unique shape, because the precise timing and positions of branch emergence from a hypha vary. This variation isn’t due to genetic differences, since identical clones from a single parent fungus still create colonies with unique shapes. Although the overall form is highly predictable, its detailed geometry is usually irreproducible. Each mycelium is like a snowflake, with a shape that arises at one place and time in the Universe.

Fungi also show evidence of learning and memory. Working with fungi isolated from grassland soil, German mycologists measured the effect of temperature changes on the growth of mycelia. When heated up quickly for a few hours, the mycelia stopped growing. When the temperature was reduced again, they bounced back from the episode by forming a series of smaller colonies from different spots across the original mycelium.