The one-sentence summary

Behaviour can be broken down into rational choices or rational guessing, and directed or undirected copying that constitutes social learning.

WHAT THE BOOK SAYS  I’ll Have What She’s Having

  • This is an extremely clever book about mapping social behaviour, co-authored by Mark Earls of Herd fame, and two anthropologists.
  • It argues that humans are first and foremost social creatures who deploy (often unwittingly) a range of copying strategies to get on in life.
  • We are certainly not blindly driven by hard-wired instincts – we know perfectly well how to use the brains of others as storage space for knowledge.
  • Cascade models help to explain many decisions, and can be likened to rivers (tributaries), trees (branches), and forest fires (ignition and spread).
  • Our social brain thinking can be tree-like, as in recursive language, which allows us to embed seemingly endless sub-bits into the main thought.
  • There are many parallels with Darwinian evolution: variation, transmission and selection apply to the spread of ideas as well as genes.
  • There are three categories for the evolution of cooperation: group mentality (kin and groups mutually benefit), reciprocity (“I’ll do it if you will”), and reputation (status gain).
  • Copying strategies really work, and include: copy the majority, successful individuals, good social learners, kin, friends, and older individuals, and ‘copy if better’.


  • Successful elements of social learning can be classified. It works best if people’s direct experience is changed by interaction; if many sparks are lit in the hope of lighting a fire; if the community is small and cohesive; the behaviour has a rationale; and the results are permanently visible and sustainable.
  • Their collective behaviour map is really useful:

1. Few people + few similar options = rational choice

2. Few people + many similar options = random guess

3. Many people + few similar options = directed copying (copy if better)

4. Many people + many similar options = undirected copying (what everyone else is doing)

  • It is notoriously difficult to change behaviour, but anyone trying to do so should read consider three approaches: 1. Identify what stands out against the background. 2. Focus on the interaction among agents in your population. 3. Learn to predict and cope with turnover.


  • This is an extremely intelligent book and, although short and well expressed, you need to be on top of your game to follow it. Concentration is crucial.