LAUSR

Computer scientists and biologists have long been excited by the idea of using nature as inspiration for the design of optimisation algorithms. Starting with the ground-breaking advent of the ant colony optimisation algorithm (ACO), which was based on the collective behaviour of trail-laying ants, research into bioinspired optimisation methods has proliferated resulting in a zoo of algorithms with names like Chicken swarm optimisation, Grey Wolf Optimisation, Elephant Search Algorithm, Moth Flame optimisation and Artificial Algae Algorithm to name just a few (reviewed by Darwish [1]). During the 1990’s, bio-inspiration was dominated by the ACO and its variants. Then, in 2000, a new model system came from an unlikely source: the then-obscure slime mould, Physarum polycephalum. Even to biologists, slime moulds like P. polycephalum are deeply bizarre organisms. Contrary to their misleading name, slime moulds are not fungi; they are giant single-celled amoebas lacking a brain, nervous system or organs [9]. Pieces cut from the main slime mould cell become fully functional individuals capable of the full range of behaviours. If those pieces are reunited at a later date, they easily merge to form a single entity. In 2000, the breathtakingly original work of Nakagaki [6,7] demonstrated that – despite lacking a brain – Physarum polycephalum was capable of finding the shortest path through a maze. Nakagaki’s [6] ground-breaking work captured the imagination of computer scientists leading to the proliferation of Physarum-inspired algorithms and models. 17 years later, Gao et al. [2] provide a comprehensive – and much needed – review that takes stock of the current field of Physarum models and computation, identifies major trends, and provides a framework which can be used to classify research achievements. In this comment, I will focus on the question posed by Gao et al. [2] in the introduction: “are Physarum-based methods superior or are they simply the current fad?”. Physarum’s popularity as a study organism is certainly on the rise; a cursory search on Web of Science for the term ‘Physarum polycephalum’ yields 2,845 publications, the majority of which are in cell and molecular biology/biochemistry, but with a significant number in ‘computer science’ and ‘multidisciplinary sciences’ (Web of Science, accessed 20 January 2019). The number of citations for Physarum polycephalum papers has been increasing steeply since 2005.