Among the Moral Penguins, there lived some males who were - not to put too fine a point on it - Sexy. They had fine black feathers, impeccably sculpted beaks, and the sort of smile that could make glaciers melt. With their good looks, they were able to, as the old penguins used to say, "warm the ice" with many lady penguins.

The Moral Penguins also had some less sexy males in the group. Generally, while these males weren't so sexy, they had something else going for them: Loyalty. When they mated, they mated for life, and reliably brought back fish to regurgitate into the mouths of their mate and chick. There was, to be sure, a certain amount of conflict between Sexy and Loyal penguins. Occasionally, a supposedly monogamous female, mated to a Loyal male, would consort with a Sexy male. For this reason, the very existence of Sexy penguins, and their promiscuous ways, undermined Loyal penguins' reproductive success.

Being Moral Penguins, rather than everyday penguins, the group had many rules, the breaking of which led to punishment. Eating carp and squid together was, for instance, banned; any penguin found combining the two in a single meal would be punished, even expelled from the group.

Then one day, a Loyal penguin had an idea. What if it were declared immoral and wrong to mate outside of a pair bond? This seemed like a good idea. Importantly, our fictitious Loyal penguin didn't have to know that preventing extra-pair activities would improve his reproductive success. The key point is that a Loyal penguin who was able to get such a rule passed would, as a consequence, do better in the fitness stakes. Thus, Loyal penguin minds are designed, we are supposing, to find such rules appealing.

Sexy penguins, of course, opposed the rule. Any rule that inhibited them - on threat of punishment - from pursuing their favored reproductive strategy was, to them, a bad idea. Again, from the standpoint of evolution, they didn't have to know why they thought it was a bad idea; they simply had to find it so, and work against it.

Different moral rules can work for or against penguins, depending on whether they are Sexy or Loyal, and we should expect penguin minds - subject to various constraints and caveats - to be designed to find those rules that promote their own reproductive success appealing, and rules that harm their own reproductive success unappealing.

Now, we can imagine that if our penguins were debating this among themselves, they might not actually talk about these strategic implications. Loyal penguins might talk about family values and the sacredness of the monogamous pair bond. Sexy penguins might talk about freedom, liberty, and the right of a penguin to do as he or she pleases. But beneath these arguments is the strategic element, using morality to advance one's own fitness interests.

So, to return to where I began in the first post in this series, recall that one of the best questions you can ask someone if you want to guess their position on drugs was: "Is sex without love OK?" We put that question, and questions getting at the same issue in the survey because we thought that people might be just a little bit like our fictitious penguins, using moral views about recreational drugs as part of the strategic game we all play with one another, favoring moral rules that give us advantages.

The broader point to take from all this is about the nature of morality. Morality is often portrayed as a very positive thing, in part because people often use the term as a synonym for "altruism." But moral rules have a sinister side, and can be used to constrain people's freedom of action, sometimes to the detriment of one group or another. This helps to explain moral disagreements: when moral rules have harmful effects on one group, but helpful effects on another, we can expect that there will be debate over the rule.

When moral rules are minted, we add to the list of things that people can't do without risking punishment. In some cases - murder, for instance - we can all more or less agree about what should be on the list. But in others, our differing strategic interests might be coloring our views of what's "right" and what's "wrong" - even if we can't say why we think so...

(The ideas in this series of blog posts are discussed in more detail in my recent book.)

Copyright Robert Kurzban 2011. All rights reserved.