The single most important insight for me about human behavior is that the brain — as with every other organ in the human body — is the result of evolution over a very long period of time.  Although not every behavior is driven by how we’re wired, the implications of the brain as an evolved organ are frequently overlooked.

One of these implications is that our brains are laggy.  That is, our environment and our wiring have been changing at different speeds, with the former charging ahead much more quickly than the latter.  Part of this is due to the inherently slow tempo of evolution: sex and survival advantages accrue across generations.  But perhaps the greater contributor to our brains’ lagginess is the profound change in our environment over an extremely short period of time.

According to Gregory Clark in A Farewell to Alms, our standard of living remained stuck in a rut until about 1800, and life expectancy was about 30 to 35 years for our hunter-gatherer ancestors… and remained unchanged until about 1800.  Nutritional challenges stunted growth as well; the average height of men from AD 1 to about AD 1800 was stuck at roughly 5′8″.  But after the Industrial Revolution, the average male got about three inches taller.

In other words, until about 1800, life was short and so were we. 

But since then — in fewer than eight generations — per capita incomes haverisen tenfold.  Better nutrition means better health.  We live longer.  We’ve grown taller.  (I’d personally like to think I’ve become more distinguished looking.)

And yet our brains are in way “stuck” in a place very long ago and very far away.  We’re still wired to throw and catch — skills that were life-sustaining back there and then — with amazing accuracy, and without having to solve nasty and complex differential equations (which is what a computer would have to do to solve a similar problem).  We harbor a natural aversion to snakes and spiders, but not to electrical outlets, fast-moving traffic, or divorce lawyers.

Which leads me to comment on the most recent books by two authors I very much enjoy: Dan Ariely and Tim Harford.  In Predictably Irrational, Dan focuses on reliable ways in which our behavior is not logical; in The Logic of Life, Tim suggests that much of what appears to be irrational can be explained by looking for the right incentive.

Although Ariely and Harford are not at full-on loggerheads, they come to very different conclusions using a shared framework: rationality.  But this framework obscures a crucial point: it isn’t whether our behavior is irrational (Ariely) or rational (Harford).  It’s whether our behavior is adaptive or maladaptive.  What Dan sees as irrational behavior can also be seen as valuable behavior that’s simply out of place — a rule of thumb that worked very well in a very different environment.  And what Tim sees as rational behavior can just as easily be seen as something that works today as well as it worked when and where our brains “grew up.”

For example, bias toward the present (or hyperbolic discounting) suggests that people very steeply discount the future.  Because many desirable behaviors involve upfront costs for downstream benefits, we plan to engage in the activities when costs and benefits are both in the future and therefore equally discounted. We then have a difficult time executing on those plans because the costs loom large relative to steeply discounted future benefits.  This is, perhaps, the fundamental challenge of wellness: In the long run, we’re better off eating less, drinking less, and exercising more.  In the short run, that’s nothing but a buzzkill.

But if you step back and think about the environment of our ancestors (and I don’t mean Uncle Al), a little light begins to dawn on Marble Head.  Back then, times were tough.  What life lacked in comfort and calories, it made up for in brevity.  Back then, chances of the long run were slim to none.  So all those behaviors that seem so virtuous today — moderation, exercise, temperance — would have been worse than useless; they’d have been a waste.

The prescription to “eat, drink and be merry” might not be sound medical advice today, but it was undoubtedly good investment advice not all that long ago.  And that’s exactly the kind of environment in which our brains were shaped.

It’s not about rationality or irrationality.  It’s about what was adaptive back then and whether it’s still adaptive today.

The lesson for practicing behavioral economists is to strive for a better understanding of the heuristics and sentiments that drive our behavior in light of the environment in which our brains were most powerfully shaped, and to determine whether those remain adaptive in today’s environment.  For those that don’t, we must work hard to retool our environments — using techniques such as choice architecture — so that yesterday’s brain succeeds today.