Rational behaviour is defined as behaviour that is based on clear, practical and scientific reasons. We tend to view people who base all their actions on rational principles as rather analytical, sometimes even cold-hearted. Most of the time we’ll contrast them to the more emotional, spontaneous persons we know. Which kind of behaviour is the right one? Should we strive for a mixture of rationality and irrationality?

Irrational behaviour is what makes us human. Do you agree? At first sight, scientific evidence seems to point in this direction. Research has shown that bees behave more rational than the average human, that is, they are better at maximizing expected utility. Evolution has done a pretty good job at stripping all the unnecessary and costly irrationalities from a bee’s mind. If a bee’s genes allow it to choose anything but the quickest and most energy efficient way, its hive won’t be the one to survive. As humans, we like to think of ourselves as way beyond the lowlands of evolution. We aren’t forced to behave in a way that maximizes expected utility all the time in order to survive. Are we better off doing it nonetheless?

The bees’ seemingly superior ability to act rational doesn’t tell us the whole story. A bee might in fact be better at fulfilling its desires than a human, but there is more to rationality than optimal goal achievement. The latter is usually termed “thin rationality” or “instrumental rationality”. Should we act according to the principles of thin rationality — always? I’d argue we should. Thin rationality, in fact, doesn’t mean more than achieving your goals in an optimal way. If my goal was to live a joyful life, why wouldn’t I do that in an optimal way? If my goal was to help others live joyful lives, shouldn’t I better pursue it rationally?

Up to now, the most important — and most distinctively human — part of the whole concept of rationality has been left out. There is thin rationality, and there is broad rationality. Remember the rational bees? According to the principles of broad rationality, they aren’t rational. Not at all. Broad rationality is the basis for our conscious choice of goals. How many bees are there which choose to change their goals? But then, how is it possible that we as humans are able to evaluate and change our goals, to choose our destiny?

In order to understand, we’ll have to look at the way our goals are structured. A few seconds of introspection and you’ll realize that there is more than one kind of goal. Psychologists often speak of first-order-desires and second-order-desires. A first-order-desire is, for instance, hunger, which could be expressed as “I’d like to eat”. An example for a second-order-desire would be an aversion regarding the desire to eat (maybe you’re on a diet), in words: “I’d like to not like to eat”.

The concept of broad rationality describes the process of evaluating both your first-order-desires and your second-order-desires, thinking about which ones deserve to be fulfilled and achieving integration of both. The fact that both your first-order-desires and your second-order-desires are likely to be influenced by forces outside yourself makes it quite difficult to decide in favor of one of these two.

First-order-desires are often caused by your genes. Your genes have only one “goal”: To replicate. It doesn’t matter whether you as the “vehicle” will profit or suffer in the course of their “plan”. Second-order-desires are prone to be the victim of another kind of replicator, the memes. A meme is any kind of belief or idea that has been or is currently part of our culture, e.g. “being thin is being beautiful”. What applies to genes, applies to memes, too: Some of them don’t act in your best interest, you as a “vehicle” are only a means to contribute to their replication.

What is so special about humans, after all? It is certainly not the “ability” to behave irrational. Irrational behaviour (in the broad meaning of the word) will lead to the replication of genes and memes which are harmful to the host — that is you. The ability to determine which of your desires are truly yours and to separate them from all the — against your will — meme- and gene-induced goals is special about us humans. Maybe we should additionally learn a lesson from the bees and make use of the principles of thin rationality to act in favor of our goals. Our own goals.