‘This is dangerous’: slime moulds and the bitter debate over the nature of intelligence

Scientists are battling over whether supposedly simple organisms should be considered ‘intelligent’. The outcome could reshape our understanding of the natural world – and our own place within it Forty years ago, as an undergraduate in Hokkaido, Toshiyuki Nakagaki came upon a lemon-yellow stain in a petri dish. That encounter turned him into a doyen of slime mould research – and fed a storm of biological and philosophical debate about the meanings of life and intelligence that persists to this day. Before, no one would have called a slime mould “intelligent”; the popular adjective, in fact, was “simple”. “A simple mass of protoplasm,” one 1895 description ran; “among the most simple of organisms”, said another. And it was hard to argue otherwise. A slime mould can appear to be just a small cell, capable only of feeding and reproducing. Simple is as simple does. Of that first meeting, Nakagaki said: “I was just impressed with how fast it moved.” Physarum polycephalum , the slime mould species in that petri dish, has a top speed of 1cm an hour. For amoebic organisms, that’s gold-medal standard. At first glance, Physarum seems to spread as irregularly as ink on blotting paper, but in fact it senses its meals of bacteria or other microbes and reaches for them with a long, thin finger of protoplasm – which not only digests its food but then forages further or pulls back into the rest of the mould. It’s impossible to watch a slime mould over many days without sensing some deliberation at play. Continue reading...