Brains are, literally, animals’ nerve centres. Sponges, jellyfish and a few other Precambrian hangovers aside, animals are usually bilaterally symmetrical, with a front and a rear. The front is where food goes in and sense organs are concentrated. Having a cluster of neurons there to interpret what is happening and organise appropriate responses is thus, as it were, a no-brainer. And to help animals get better and better at responding, brains are also good at learning.

One class of learned behaviours is habits. These are usually helpful (the alternative, actually thinking about things, is tiring), but not always. Bad habits can be hard to shed, and even some theoretically good ones, like exercising regularly, are hard to learn. But understanding the brain mechanisms underpinning these processes can help.

Such knowledge about large brains, like those of humans, is still crude. For small ones, like those of flies, though, it is now possible to trace every neuron and connection. Understanding how those neurons and connections combine to learn things is still a work in progress. Insights from artificial intelligence may be useful. The breakthrough that will lead to a real understanding of consciousness, though, is elusive.