The vast majority of species on Earth are single-celled. Most of these languish in obscurity – many have never even been named – but some of the relatively few species that have been studied exhibit remarkable abilities.

Many single-celled organisms can work out how many other bacteria of their own species, are in their vicinity – an ability known as "quorum sensing".

Many different species live side by side in these "bacterial cities", munching one another's wastes, cooperating to exploit food sources, and safeguarding one another from external threats – such as antibiotics.