Morality as an Evolutionarily Stable Strategy: A Naturalistic Account of Libertarianism
The ESS can be explained by way of an illustrative example.2 In provisioning their nests, female digger wasps follow two distinct strategies: burrow or borrow. The ﬁrst strategy is to burrow a hole in the ground, catch and paralyse four or ﬁve katydids, deposit them into the hole one at a time, lay an egg on the top of the pile, and then seal up the hole before beginning the process all over again. The second strategy is to search for an abandoned hole, provision it, lay an egg, seal up the hole, and go looking for another one. The second strategy might seem advantageous relative to the ﬁrst, since it exploits the digging efforts of others. But it has a disadvantage, too: if the hole has not really been abandoned, then the intruder might spend time and effort provisioning it only to have its digger return, lay her egg and seal it up. If too many wasps employ the second strategy, available holes become scarce and the chances of double-occupancy go up; whereas if too many wasps dig their own holes, then some will be abandoned and digging efforts will go to waste. There is therefore a critical frequency at which the two strategies are equally and optimally beneﬁcial, and the population of digger wasps settles into an evolutionarily stable state around that critical frequency.