Here’s the riff (developed from the paper I delivered at the recent AAP conference): because the success* of behavioural strategies – including moral strategies – depends on the environmental conditions in which the agent is situated, and because that environment includes the strategies employed by other agents, it pays to Mix It Up A Bit in terms of the strategies employed by the population.
As a result, you’d expect to see a diversity – or a ‘pluralism’ or ‘polymorphism’ – of strategies employed in a population. Some will be ‘nice’, some will be ‘suspicious’. That’s what I call Lesser Moral Diversity. Some will be ‘nice’, some ‘suspicious’, some ‘nasty’. That’s what I call Greater Moral Diversity. Details below:
Some adaptive problems are relatively static against the background environment; how to transport energy between cells is a relatively static problem, and it has been more or less solved with the evolution of the astounding ATP molecule. Discovering the solution to problems such as these is modelled by decision theory – which looks at ‘single player games’, where one agent is working to find a solution to a problem against some static (if imperfectly known) background conditions.
However, some adaptive problems aren’t situated against a static background. In these cases the success of a particular solution depends on the solution chosen by other agents or aspects of the environment that changes depending on the agent’s chosen solution. For example, consider the arms races that take place between certain predators and their prey: one side evolves a new defence mechanism, the other evolves a way around it. These problems are modelled by game theory, a favourite of this blog.
As another example of a dynamic adaptive problem, consider the immune system, and the major histocompatibility complex (MHC) in particular. The MHC is a large region on our genome – and the genomes of almost all other vertebrates – that is central to our adaptive immune system, which is the part of our immune system that identifies and reacts to invaders and pathogens that enter our body. The MHC provides a mechanism for our immune cells – primarily killer T cells – to identify friendly ‘self’ cells produced by the body from potentially harmful ‘nonself’ cells.
Interestingly, the MHC region on the genome is incredibly polymorphic, meaning it varies tremendously between individuals of the same species. This is interesting because most parts of our genomes are drastically less polymorphic – meaning there’s less variation – because evolution has slowly gravitated towards one, or a small set of, solutions to a particular problem. Or, when it comes to traits that have little adaptive significance, such as eye colour, there’s little selection pressure to encourage the evolution of more alleles, such as yellow or orange eye colours.
But with the MHC it appears as though something has actively been driving the high polymorphism – something has been encouraging new mutations to stick around and join in the big pool of alleles. There were a number of theories proposed to account for this polymorphism, such as overdominance selection – which is where heterozygotes have a greater adaptive advantage compared to homozygotes, thus encouraging polymorphism in that trait. The paragon example of overdominance is that of sickle-cell anaemia versus malaria.
But it seems the most important force is frequency-dependent selection. This is where the selective benefit of a trait is dependent on the frequency of other traits in a population. To take a fairly banal abstract example, consider a gene that encourages an animal to seek out the lowest fruit on a tree. Seems to be plenty of advantages to such a strategy. But if that gene is rife in a population, all the lowest fruit on trees will be subject to fierce competition. In such an environment it might be more fruitful (no pun intended) to seek out fruit higher up the tree, with the cost of picking that fruit compensated for by less competition with other members of your species. But, if this second gene raises in frequency sufficiently, then there’ll be increased competition over the higher fruit. And on it goes.
Likewise our immune system, is constantly adapting to the evolving threats in our environment, such as new mutations of viruses like influenza. As viruses mutate and adapt to the more common genotypes, it’s the more novel or rare genotypes that are likely to survive infection or a widespread epidemic. High polymorphism in a population thus reduces the likelihood of a devastating pandemic that kills most or all of the population. And because the pathogens are constantly adapting, so too does our immune system have to keep adapting.
Now consider our moral sentiments that motivate moral behaviour. The more ‘nice’ people there are in your population, the more benefit you’ll get from employing a ‘nasty’ strategy. Yet a sufficient number of ‘nice’ strategies working together will out-compete ‘nasty’ strategies. Ultimately, there is no one solution that will dominate in every environment, so you’ll end up with a polymorphism of strategies.
We know that genes influence an individual’s moral sentiments – although environment and culture also have a great influence. So we’d expect there to be a polymorphism in the genes that influence moral sentiments. This polymorphism might only result in a small variation in the emotional responses of one individual compared to another, but this small variation might be amplified by cultural forces and experience to produce a more pronounced difference in personality: for example, someone with a higher empathy response might be drawn to ideologies that favour cooperation over competition, and that might amplify their empathy strategies.
Lesser Moral Diversity is the thesis that we’d expect to see a polymorphism within a population of ‘nice’ (or, coarsely, ‘liberal’) strategies and ‘suspicious’ (or ‘conservative’) strategies. Greater Moral Diversity just extends this slightly to include strategies that we’d consider immoral, or ‘nasty’, such as are employed by psychopaths, and suggests that we’d expect a certain percentage of these strategies within a population as well. Equilibrium is found dynamically rather than gravitating to a single ESS, like with the MHC.
That’s evolved moral diversity.
* By “success” I mean, in evolutionary terms, reproductive fitness – i.e. the number of related offspring (and grand offspring) and individual can produce. Not that reproductive fitness is the goal of morality today, of course…