The Iterated Prisoner's Dilemma

Critical to fully understanding the evolution of behavioural traits is understanding some basic game theory, such as the iterated prisoner's dilemma.

The basic prisoner's dilemma is as follows: two criminals are taken to the police station and interviewed separately. They went on a crime spree together and there is enough evidence to convict them of some of the minor offences. Imagine you are one of the prisoners and you are given a choice, which you assume your partner in crime has also been given: confess to everything and thereby grass up your partner for the major charges [defect]; or keep your mouth shut [cooperate]. If you talk and your partner doesn't, then you get a reduced sentence of 2 years in prison because of helping to convict your partner; and he gets 10 years. If he talks and you don't then obviously the reverse happens. If you both give a full confession then you both get 8 years, and if neither of you talk you both get 4 years. What do you do?

Now imagine that you and your partner can both live forever, and any time either of you are not in prison you go on another crime spree together and each time you get caught and face the same decision. You know your partner's previous responses, so this will obviously affect whether you cooperate or defect in the latest interview with the police. This situation is the iterated prisoner's dilemma, and occurs (in other forms!) every day in societal life (the social contract).

The various consequences to the options can be formalised into a pay-off matrix, and different weightings given to the possible outcomes. So long as all the options are sensible, for example the benefit to you for defecting when your partner cooperates should always be more than the benefit to you for cooperating when your partner cooperates, then it is possible to make some firm conclusions about the worth of different strategies.

Axelrod created a tournament in which different programs played against each other (200 iterations for one game) and then each program's total score was added up. Some of these programs had very sophisticated algorithms to predict whether the opponent would cooperate or defect, however the overall winner was a program called tit-for-tat which simply started out cooperating and then did whatever the opponent had done the previous move. In the second tournament the winner was called tit-for-2-tats, I don't think I need to explain that one's tactics!

It is important to note that in a population it isn't as simple as there being an optimum strategy that everyone should abide by. One of the founders of modern game theory, John Nash (of “A Beautiful Mind”), showed that strategies of cooperation and defection settle to a balance (the Nash equilibrium) – so long as the frequency of defection is low, then on average the cooperators gain by continuing to cooperate and the small number of defectors can take advantage.

Emotions Part3

Love

Have you read Part1 and Part2?

Evolution depends on procreation of offspring that live to successfully procreate themselves. When a woman becomes pregnant she is vulnerable, and, in our past, would not be able to look after and feed herself. When she gives birth this remains true, and the early years of the infant have a high relative mortality rate (by this I mean that if a child survives the first couple of years, there is a high probability it will make it to adulthood).

This means that it is an evolutionarily fit strategy for men and women to couple off for at least a few years – to ensure their genes are passed on successfully.

When choosing a mate, you want to select the best mate that will also be happy to have you, and for that selection period to not be too long. As an interesting aside, game theorists can prove the best strategy for a game like this is to evaluate the potential mates you meet for 36.8% of your acceptable time period (1/e) and then mate with the next one that comes along that is better than the best option of the evaluation period. For example, if you wish to settle down between the ages of 18 and 32 then 37% of that window is 5 years, so you should settle for the first person you are presented with who is better than anyone you've met up to that point at the age of 18 + 5 = 23 years old.

What if a better option is presented to a man in the period shortly after he gets his woman pregnant? Would it not be in his interest to switch? Yes, but if this happened at a high frequency in a population then it would not be a good strategy on average. A woman needs to believe that her man will stick around and so men do not tend to 'decide' to be with their mate for rational reasons that could be trumped by a better woman round the corner, but they fall in love instead. Love acts a bit like the doomsday device explained in part 1; it says to a potential mate, “I am with you for irrational reasons, and so there is no reason why I will leave you.” The feeling, to be trustworthy to the mate, must be accompanied by difficult to fake physiological symptoms.

It is possible to take a blood test to see if you are in love. The telltale chemical/hormonal signature lasts approximately 30 months. This is, predictably, roughly the length of time between conception and the child exiting the high-risk early years.

When a man has sex he is less committed to caring for the woman and child, whereas if the woman gets pregnant, she is committed to becoming more vulnerable and expending a lot of resources to have a child. Therefore it makes sense that sex will lead to feelings of love more easily for women than men.

Emotions Part2

Why do some people not have them?

(please read part1 for context)

Emotions are evolutionarily valuable if the outward signs are difficult to mask; a fake smile is controlled by the cerebral cortex, and looks different to the natural smile created by the limbic system. However, if the proportion of players that can convincingly fake emotions is at a low frequency, then the majority do not change their life tactics and the rare ability to be a great deceiver gives enough evolutionary advantage to keep those genes in the population.

This explains why Antisocial Personality Disorder is to be expected at low frequency in any population – with the frequency affected by the type of society. I would guess that a society with low mobility and a high cost of being found out (dishonour=shunned forever) would have a lower incidence of sociopathy, but I am unaware of any research to bear this out either way.

Sociopaths may feel the limbic emotions, but not the ones generated in the neocortex (probably related to the smaller amygdala and reduced grey matter in the prefrontal cortex found in the brains of sociopaths). However, they are very capable of reading the emotions of others (in contrast to autistic spectrum traits, which also include lack of complex emotions such as empathy).

There is some evidence that children below the age of 5 or 6 do not have a fully developed neocortex and so are often seen to exhibit sociopathic traits that demonstrate lack of empathy, violence, and emotional manipulation. For example, young children will often look distraught and in tears but when given their toy back will immediately turn it off and appear happy again. In this case, is the child really experiencing the emotion, or are they just simulating it to manipulate their way to what they want?

Of course, as always, the truth is a mixture of many things – a genetic component is proved, and the preponderance towards males being sociopathic is some evidence of a link with autism. This sex divide may be due to genes on the Y chromosome, or possibly due to gene interaction with testosterone.

Nurture can play a role through someone being desensitised to emotions as a defence mechanism from an abusive upbringing. Nurture and environment could also play a role by activating genes.

All the above should be taken as opinion – there is some research material available on sociopaths, but it mostly deals with the incarcerated violent ones as test subjects and so presents a very skewed view of the phenomenon.

click here for Part3

Emotions Part1

Part 1 Why do we have them?

In 1952 McClean proposed a model of the brain as consisting of 3 parts; the stem, the limbic brain, and the neocortex. Brain physiology certainly shows distinct structures within the brain. He advocated the theory that as the brain evolved it did so, not by fluid wholescale changes, but, by adding on modules (which gradually became bigger and more complex). The original function of the stem brain did not change, but the extra functional capabilities of the limbic brain were added and then later the neocortex (where higher processing and consciousness occur) was added.

In 1980 Plutchik posited that basic emotions were rooted in the limbic brain – fear, disgust, anger – and that higher emotions springing from our social interactions were rooted in the neocortex – guilt, love, sympathy.

In 1990 Nesse furthered these models by using the language of game theory. He assigned emotions to the possible emotional states produced by the iterative prisoner's dilemma:

When both players cooperate they feel friendship, love, loyalty, obligation, pride.

When both players defect they feel hatred and rejection.

When one cooperates the cooperator feels anger and the defector feels guilt.

If someone looks happy and friendly you can predict that they are probably a cooperator. If they look angry/guilty then they are probably a defector and you should avoid cooperation in a social contract with them.

Another useful theory when considering emotions is that they may limit violence in squabbles. If there is a disagreement between obviously physically mismatched people then logically the weaker should simply concede. However, by displaying emotion like anger the weaker one signals that they may not act rationally and so the stronger should think twice about escalating a conflict. Fans of Dr Strangelove will recognise this as being analogous to the doomsday device; protection by Mutually Assured Destruction.

click here for part2