To Lucy, an editor, the question – which she had not been prepared for – over a lunch as to what to her is important in life elicited immediately the idea of ‘connectivity’.

The reptilian part of our brain predates the mammalian part by a long way; the ‘rational’ part evolved relatively recently. The mammalian part developed when amphibians evolved into mammals, who suckle their young and divide tasks among the community, surviving as a group and not as individuals. The impetus whereby we should, and need to, communicate with one another, relate to one another, look out for one another, watch one another’s back, and so forth is integral to the sort of creatures we are, and so is of prime importance. Even a hermit would feel the need to connect with someone or something – that might be God/god and/or, failing our own kind, other animals and the whole natural world.

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Dummy’s Guide: evolution of the human brain

Reptilian: 700m years old, linked to the autonomous nervous system: survival & territorial instincts & reflexes (fight, flight, freeze or fawn); maintains bodily functions.

Mammalian: 70m years old, linked to the limbic system: curiosity, emotion, nurturing, altruism, social structures.

Rational: 19–15m years old, neocortex & surrounding thalamic structures: analysis, reasoning, imagining, language & symbols, self-awareness. While other animals have smooth neocortices, the human’s is grooved and ridged, which vastly increases its surface area. The development & maturation of the prefrontal cortex occurs primarily during adolescence until the age of 25.