Levin and Yuste in aeon:
Intelligent decision-making doesn’t require a brain. You were capable of it before you even had one. Beginning life as a single fertilised egg, you divided and became a mass of genetically identical cells. They chattered among themselves to fashion a complex anatomical structure – your body. Even more remarkably, if you had split in two as an embryo, each half would have been able to replace what was missing, leaving you as one of two identical (monozygotic) twins. Likewise, if two mouse embryos are mushed together like a snowball, a single, normal mouse results. Just how do these embryos know what to do? We have no technology yet that has this degree of plasticity – recognising a deviation from the normal course of events and responding to achieve the same outcome overall.
This is intelligence in action: the ability to reach a particular goal or solve a problem by undertaking new steps in the face of changing circumstances. It’s evident not just in intelligent people and mammals and birds and cephalopods, but also cells and tissues, individual neurons and networks of neurons, viruses, ribosomes and RNA fragments, down to motor proteins and molecular networks. Across all these scales, living things solve problems and achieve goals by flexibly navigating different spaces – metabolic, physiological, genetic, cognitive, behavioural.
But how did intelligence emerge in biology?