Do we bend it like Beckham?

This post is part of a small series of posts on social learning and cooperation.

Jean-Baptiste's reaction to Laurent Lehmann's (and his colleagues') criticism of Boyd and Richerson's models made me brood over the notion of prestige-biased imitation. This notion is central to their whole system: both to their theory of cutural inheritance, and to their theory of cooperation through cultural group selection. But let me explain...

Robert Boyd likes to illustrate prestige-biased imitation with this picture of David Beckham lending his name and face to sell razorblades. Advertisement moguls (not exactly the epitome of scientific rigor) claim that having Beckham on the ad greatly improves its efficiency, and big business executives (not exactly the embodiment of rationality either) are willing to follow them. Let us suppose that they're right. Let us make the additional supposition that Beckham's face does not work merely by attracting people's attention on the ad (for it would imply that our friends, the rational businessman and the rigorous ads mogul, would be wasting too much money on a trivial result). Then, we have to conclude, people are buying these razorblades on the recommendation of David Beckham.

Now, Robert Boyd remarks, David Beckham is just a footballer - sometimes a poorly-shaven one at that. Why would one copy his choice of razorblades?

"Prestige-biased imitation" is the explanation. In our ancestral environment, the story goes, it was much more difficult to find an appropriate response to life's challenges, than to simply copy the most successful individuals around us. These individuals were skillful and knowledgeable: they knew useful techniques and bits of information that helped them survive this famously harsh Pleistocene environment of ours. Because of that, they were successful: they had more power, and food, and mates. And because of their success, they were prestigious: they elicited signs of deference from others, even when they were not in a position to dominate them.

Since prestige is such a good indicator of success, and success, in turn, such a good predictor of survival skills, it made sense for us to imitate our fellow humans on the basis of the prestige they had in our society (now is not the time for a Proustian note on the social relativity of prestige - huge variations in the value assigned to individual from one social setting to the next). Evolution thus gave us a motivation to imitate prestigious and/or successful, and/or skillfull individuals. At the end of the day, the theory predicts that if a fellow human is sufficiently presitigious, successful and skillful, we tend to imitate everything he does. Like buying razorblades or marrying Posh Spice.

If true, this psychological hypothesis obviously has momentuous consequences for cultural evolution. Among other things, it predicts that, if David Beckham becomes a secluded Buddhist Monk, or a suicide bomber, a small but significant proportion of the world population will do so. And conversely, if many humans do things like giving away their lives for religious or political causes - something you do not see among other animals, but quite often among humans, chances are that somewhere, sometime, a Pleistocene David Beckham decided to give away his life for a cause.

The bearded Beckham

Is prestige-biased imitation based on prestige?

In order for the theory to work, Laurent Lehmann et al. have shown (in accordance with previous work by Boyd and Richerson) that prestige-based imitation must obey two criteria: first, it has to be independent of the actual content of the behavior that is copied (in the words of the theory, it has to be context-dependent, not content-dependent).

In other words, when you imitate David Beckham by buying razorblades, your decision has to be based on David Beckham's charisma alone, and not on some inference you made about what the razorblades do. Suppose, for instance, that you chose to buy the razorblades because you believe they are responsible for Beckham's subtle, artful, faux négligé three-days beard - after all, TV lore teaches that there is a direct causal link between a good razorblade and a great sex life (I see our friend the ad mogul nodding).  Then your decision is based on information that ultimately has to do with razorblades - and sex - but not with Beckham. The advertisement team has wasted money paying him: a nobody with a great 3-days beard woul have done the deal.

You might also have bought Beckham's razorblades because you were under the impression that they contributed significantly to his winning the heart of a former Spice Girl - which many people consider a success in life, at least in the UK. In that case, the advertisers lost their money on Beckham all the same: any other former-Spice-Girl's husband would have done the deal, at a cheaper price.

In both these cases, your decision did not originate in your admiration for Beckham, but in the perceived effects of buying a razorblades, as evidenced by the case of David Beckham. You were influenced either by David Beckham's supposed skills in choosing rasors, or by David Beckham's success.

To many contemporary defenders of the theory, like Joseph Henrich or Richard McElreath, this argument cuts little ice. Whether it is Beckham's skills, his success or his prestige that influenced you, it remains that David Beckham's presence on the ad prompted you to imitate him. There is, they argue, a total continuity between skills, success and prestige: it makes no difference to the human mind and its deeply-rooted imitation instincts. The rest is  philosophical picking.

For example, to these authors (I am using an example from McElreath), if I copy farmer X because I have seen him plant a new crop that gives far better yields than other crops, which of course caused him to gain much money, this is an instance of prestige-biased imitation, also known as success-biased, skills-biased imitation. It has everything to do with what I think about farmer X (even if that's the only thing I know about him). It has nothing to do with what I learnt about the new crop when observing farmer X.

There may be more than a conceptual difficulty here. This broad definition of prestige, as including skills and success, is a way to dispose of many embarrassing cases where imitation is content-dependent (i.e. mindful of skills and of their outcomes, and not easily swayed by prestige), and define them away as prestige-biased imitation, hence completely context-dependent. In that way, most cases where our imitation is based on information that we get about the world while observing others, trying to find out what strategies are best for us,  free from social prejudice, are pushed under the rug. Social influence is everything.

What happens if we don't push all these instances of imitation not based on prestige under the rug? This: if your decision to buy the same razors as Beckham was not based on Beckham himself, but rather on his good looks, or on his decent (by Girls-Band standards) romantic life, then you have no reason whatsoever to imitate him when he decides to become a suicide bomber or a Buddhist Monk. And advertisers lost their money.

The stupidity argument

A possible line of defence might be the following: we might dissociate Beckham's skills and successes from his prestige, if we were clever enough to do so. But we're not. Evolution has programmed us once and for all with a motivation for which prestige trumps everything else. The kind of razors that Beckham uses are completely irrelevant to his football success - but we are too dumb to see that. If somebody is prestigious, our imitation instinct will just tell us to imitate him in all other respects. Joseph Henrich remarks that prestigious people are deemed better than other on a wide range of performances, even in fields so far away from their original domain of skill and success that we have no good reason not to trust them there (I have been told that Juliette Binoche's recent dancing performance confirmed Henrich's view).

To put it another way, evolution has equipped us with the starkest rule of thumb to survive in society: copy the most prestigious individual, whatever he does. In order for this rule of thumb to work well enough to keep us alive as a species, two assumptions would have to be met: first, skills should be tightly correlated with mating success and power; second, revision rules that may prevent us from following an unskilled leader, by letting us realize his incompetence, should be so costly to maintain that it would never evolve, even though  its absence would cost the death of a great number of individuals.

Skills not rewarded

We all know that, in a given society, skills and success/prestige may not be present together. At least George Bush Jr. taught us that. How much decorrelated can they be? If the correlation has to be between a person's prestige and the majority of her skills (opening a bottle, making allies, singing, swallowing Bretzels, etc.), as the theory demands, it seems  obvious that, while she might derive much success from a handful of special skills in which she is gifted, there is no reason to expect her to be significantly more gifted than all her social inferiors in the majority of their skills.

This problem is especially vivid since Boyd, Richerson and Henrich often claim that their theory works best under conditions of extreme uncertainty (humans, the story goes, developped their imitating habit as a way to acquire cultural knowledge, that helped them adapt to a fast-changing Pleistocene climate). The problem with extremely uncertain environments, in which randomness plays a great part, is that they tend to decorrelate skills and success. Think of it this way: if I am a good hunter hunting in a very steady population of rabbits with regular habits, the result of my hunt does not have much to do with the rabbit population. I will regularly outperform less gifted hunters. But suppose the rabbit population begins to fluctuate violently, with rabbits popping up at the most unexpected times and places: it will increase the odds that I come back from the hunt without a rabbit to show for my great skills. If, however, someone comes back from hunting with rabbits aplenty, this will not be a good indicator of his hunting skills. He might just have gotten lucky. The informational value of hunting success will decrease: they will no longer be good indicators of hunting skills.

I will just sketch my second argument: it is extremely costly to imitate David Beckham when he decides to become a Monk or a suicide bomber, because that reduces one's fitness to zero. We do have the capacity to see the consequences of Beckham's idealistic actions and the detrimental consequences of imitating him: if we are not blind to success or skills, we should similarly be aware of failures and incompetence. If prestige-imitation causes us to disregard them (and it has to, otherwise fitness dictates us not to imitate stupid people and failures, prestigious though they might be), we should assume that, for some reason, it is impossible for our prestige-biased imitation mechanism to take them into account.

Is imitation ever genuinely blind and prestige-biased ?

I have no proper conclusion to offer, only a challenge: I am not aware of any good study unambiguously showing a case where imitation is clearly detrimental to the imitator, and clearly motivated by the model's prestige alone (that is, excluding his perceived skills or his success, real, expected or assumed). The only example I have been given is waves of suicide among teenagers following the deaths of Marilyn, Kurt Cobain, or the litterary suicide of Young Werther - from whom these waves got their names of "Werther effects". I find the evidence of such waves quite sloppy and anecdotal, with many biases in the treatement of data - discounting the fact that the suicide rate was already on the rise before the allegedly imitated suicide took place is a frequent move in suicide wave studies. The only case that seems genuine to me, is the first one - Werther. Sadly, Young Werther was neither prestigious, nor successful, nor skillful, nor real.

Reference:
The version of dual-inheritance theory this post refers to can be found in chapter 2 of Henrich, J. and Henrich, N., Why Humans Cooperate: a cultural and evolutionary explanation,. Oxford University Press, 2007. Their formulation has the advantage of being recent and extremely clear. I am not sure to what extent other theorists like Robert Boyd endorse some aspects of it, like skill-biased imitation being equivalent to prestige-biased imitation.