February 12, 2014


On page 534 of Volume 2 of On What Matters, Parfit writes1:

If our normative beliefs were mostly produced by evolutionary forces, we would expect that we would have beliefs that were reproductively advantageous, by making it likely that we would have more descendants.

If we ask which normative beliefs would be most likely to have this effect, there are some obvious answers. We would believe that we have strong reasons to try to have as many surviving children as we can, as an end in itself, and not merely because having children would promote our own well-being. But most people do not believe that they have such reasons. When people have become able to use artificial birth control, most of them have chosen to have fewer children.

We can similarly claim that, if our moral beliefs were mostly produced by evolutionary forces, we would expect people to believe that they have a duty to have and raise as many children as they can, and that deciding not to have children would be wrong. But this is not what people have believed. Those who decide to have no children have often been revered or admired. If our normative beliefs were selected to maximize the number of our descendents, and of other people who have our genes, these various facts would be hard to explain.


I was rather disappointed with this argument.

In my opinion, the idea that our modern normative beliefs are largely the product of evolutionary forces is best attacked by appealing to the extent that our normative beliefs have been transformed2 in the last hundred years, a period of time far too small for the literally glacial pace of evolution to effect such far-reaching changes.

Instead of presenting stronger defeaters like the one I just adumbrated, Parfit begins to enumerate a number of “obvious” normative beliefs we would apparently have if our normative beliefs actually were largely produced by evolution, including the belief that we should have as many children as possible, and the belief that we shouldn’t use birth control. We don’t have these beliefs, ergo, Parfit claims, evolution didn’t produce our normative beliefs.


Unfortunately, running this argument (especially adorned with the examples Parfit gives) requires an almost Creationist-level interpretation of evolution. Offspring number, for instance, is a well-studied parameter that is strongly predicted by a number of evolutionary models. Many of these models are predictive across a huge numbers of species. One such model, parental investment theory, provides a way to understand the enormous variance in offspring number across species as contingent upon the limited parental resource budget that must be divided among offspring.

Offspring number reaches equilibrium in a staggeringly multidimensional space involving lifespan, predation risk, resource availability, mate selection, gestation period, age of sexual maturity, etc. A trivial example: a recent study involving Melospiza melodia (the song sparrow) showed that raising the percieved risk of predation by playing recordings of predator calls reduced offspring number by 40%. Other examples abound, but Parfit seems content to ignore the vast biological literature that is relevant here, preferring to bludgeon through the argument with the assumption that evolution always favours greater offspring number.


I think cariacatures of evolutionary arguments, even if unintentional, are a fantastic way to remain unengaged with the burgeoning, fascinating, sometimes wonderfully empirical, and sometimes wildly overspeculative literature surrounding the evolutionary basis of morality. The neurochemical correlates of empathy and trust, the adaptive advantage of an altruistic disposition, the enormous adaptive advantage of the prefrontal cortex that enables us to do moral philosophy in the first place- this is rich, lustrous material for philosophical argumentation. I would love to see a mind like Parfit build his arguments out of stuff like this.

  1. I’ve added paragraphs for clarity

  2. In attitudes towards other races, slavery, homosexuals, etc.