many institutions formed by human societies are designed so that they can function only when a prescribed minimum number of members are present. Familiar instances are parliaments and boards of management. The idea, presumably, is to ensure that a handful of individuals do not hijack the institution. Curiously, cellular and animal societies, too, contain examples of quorum-based behaviour.

In higher animals, during the formation and development of the embryo, the process of differentiation (wherein cells commit to a specialised pathway) appears to require more than one cell to be in step at the same time: differentiation is inherently a