Who needs a brain? Slime moulds, behavioural ecology and minimal cognition

Although human decision making seems complex, there is evidence that many decisions are grounded in simple heuristics. Such heuristic models of decision making are widespread in nature. To understand how and why different forms of information processing evolve, it is insightful to study the minimal requirements for cognition. Here, we explore the minimally cognitive behaviour of the acellular slime mould, Physarum polycephalum, in order to discuss the ecological pressures that lead to the development of information processing mechanisms. We discuss evidence for memory, basic forms of learning and economically irrational choice in P. polycephalum. We compare P. polycephalum’s behaviour with a number of other non-neuronal organisms in order to question the evolutionary need for complex nervous systems to develop cognitive traits. By highlighting a few examples of common mechanisms, we conclude that all organisms contain the building blocks for more complex information processing. Returning the debate about cognition to the biological basics demystifies some of the confusion around the term ‘cognition’.