Skip to content
Spiral Staircase
Buy the book
Menu

Glossary

Social brain hypothesis

Defined in topic 3

Robin Dunbar's 1998 argument that primate brains grew to manage social relationships. Diet, ecological problem-solving and the storage of learned culture are live rivals; no single pressure has won.

Published Updated

Where this comes from

In the reference topic that owns this term

Reference topic 3, The Expensive Organ, states the mismatch as a card: what the system evolved to expect, what it gets instead, and what happens in the gap.

Mismatch card

What it expects

Cooked, varied food; sleep; a band of about 30 people inside a wider network; daily physical and mental challenge.

What it gets

Long hours seated (Topic 6), isolation for some, and prices, deadlines and risks its defaults never met.

What happens in the gap

Defaults misfire as worry, the planning fallacy and reluctance to part with what you own; isolation and inactivity are associated with smaller brain structures and higher dementia risk.

The full card, and the topic behind it

What that chapter recommends

3 of the 7 graded recommendations in Reference topic 3, strongest evidence first. How the grades work.

  1. Sleep 7 or more hours a night on a regular basis

    ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

    the consensus of American sleep medicine. ●●○ Loud snoring, gasping or daytime sleepiness warrant a sleep assessment. See Chapters 23 and 41.

    Read it in full

  2. Keep people in your week

    ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

    Social isolation is one of 14 modifiable risk factors; addressing all of them might prevent about 45% of dementia. ●●○ (observational) See Chapters 29 and 42.

    Read it in full

  3. Walk briskly, and build up gradually

    ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

    In a trial of 120 older adults, walking 40 minutes three times a week for a year, after building up from 10 minutes over seven weeks, enlarged the anterior (front) hippocampus by 2%.

    Read it in full

Related terms

The argument behind this term, its studies and its notes are in Reference topic 3 of the reference library. The book gives the practical version. Get the book.