I am in two minds about Doug Kenrick and Vlad Griskevicius’s The Rational Animal: How Evolution Made Us Smarter Than We Think. As an introduction to evolutionary psychology and the idea that evolutionary psychology could add a lot of value to economics - and behavioural economics in particular - it does a pretty good job.

On the other hand, the occasional straw man discussion of economics and the forced attempt to sex up the book kept distracting me from the central argument, so I never found myself really enjoying the reading experience. Then there is the heavy reliance on priming research - more on that later.

The basic argument of the book is that people are deeply rational. Today’s choices “reflect a deep-seated evolutionary wisdom”. That wisdom sometimes works well, but we can have an impression that behaviour is irrational because we do not understand what people are trying to achieve. And sometimes this wisdom backfires when the environment is different from the one in which we evolved.

Importantly - and I struggle with this point - they argue that humans pursue several different evolutionary goals and the evolutionary goal that is on someone’s mind at a particular moment will affect the decisions they make. Someone will make a different decision if thinking about acquiring a mate as opposed to responding to a threat to their safety.

Kenrick and Griskevicius identify seven sub-selves that relate to specific evolutionary goals - self-protection, disease avoidance, alliance building, status building, mate acquisition, mate retention and care of kin. When thinking of mate acquisition, we will be interested in demonstrating our value over others. When self protection becomes the focus, we will be happier mixing in with the crowd. Most of the book is an examination of how these sub-selves affect our decision making, including how they vary between the sexes and change over our lifespan.

As a neat example (although note my comments below about priming), people watched a clip from one of two movies, The Shining and the romantic Before Sunrise. They then saw a set of commercials in which products were promoted as being popular (e.g. “visited by over a million people a year”) or unique (e.g. “limited edition”). Those who saw the ads after seeing the clip about The Shining preferred popular products (safety in numbers), while those who saw the romantic film preferred unique products (to attract a mate you need to stand out from the crowd). Different films triggered different sub-selves and accordingly, different decisions.

Through the book, here are a few of the random snippets that I bookmarked:

  • A classic behavioural science problem involves framing a choice between two disease treatments. One group has a choice between saving 200 of 600 people, or having a 33% chance of saving all 600. A second group has a choice between 400 of 600 people dying or a 33% chance that no-one will die. Those who hear the first (positive) framing tend to choose the certain treatment, but most choose the uncertain treatment in the second (negative frame). However, those numbers differ from the typical group size of our evolutionary past - around one hundred people. X. T. Wang found that when the same problem was framed with numbers similar to an ancestral band - i.e. 20 of 60 will be saved - the framing effect disappears.

  • When the prisoner’s dilemma is played between brothers, the payoffs from an inclusive fitness perspective encourage cooperation, and that is what we see.

  • When something is coming toward us - say a rock at our head - our brain tells us it will hit sooner than actually will. It’s an error, but making a predictable error in this direction is not a bad thing. There are asymmetric costs to an error in either direction. The propensity to sense that an approaching object will arrive sooner than it will is called auditory looming.

  • Just seeing diseased people can trigger an immune system response.

Now to the main issue that gnawed at me through the book. The arguments heavily draw on research in priming, which is not faring particularly well through the failure to replicate many priming studies and evidence of publication bias. I’ve been willing to give some benefit of the doubt to priming research in evolutionary psychology, as there seems to be some basis for it. It feels reasonable that seeing picture of an attractive woman - even if it is just a picture - could result in more mating-related behaviour (well, certainly more of a basis for that than reading words related to the elderly and walking more slowly).

Alas, even the work in this space seems to be falling apart. I’ve cited that work in my published papers, and believe that many of the underlying phenomena are there (for instance, men taking more risk in the presence of attractive women), but it looks like priming is not the way to show this.