Isolated prisoners’ dilemmas were rare in the ancestral environment—most PD-like interactions took place in a social environment where they would (at least in expectation) have indirect effects either within a particular relationship or on one’s broader reputation (and thus shared features with an indefinitely iterated PD). So the advantages of being good at PD-in-a-social-context far outweighed the possible benefits of consistently defecting in the rare truly one-shot PD. That means most of evolution’s optimization power went towards building in adaptations that were good at PD-in-a-social-context, even if the adaptation made one less likely to defect in a truly one-shot PD.
For example, people tend to internalize their reputation, and to feel bad when others disapprove of them (either a particular close other or one’s broader reputation). Having a model of how others will react to your behavior, which is readily accessible and closely tied to your motivations, is very useful for PD-in-a-social-context, but it will make it harder to defect in a one-shot PD.
Another adaptation is the capability of feeling close to another individual, in such a way that you like & trust them and feel motivated to do things that help them. This adaptation probably involved repurposing the machinery that makes parents love their offspring (it involves the hormone Oxytocin), and it makes it harder to defect on the last turn. For actions towards one’s offspring, evolution didn’t want us to defect on the last turn. Adding last-turn defection in non-kin relationships seems like a lot of complexity for a low return, with a potentially high cost if the adaptation isn’t narrowly targeted and has collateral damage towards kin or earlier turns.
There are also various specific emotions which encourage TFT-like-behavior, like gratitude and vindictiveness. Someone who spends their last words on their deathbed praising the person who helped them, or cursing the person who cheated them, is cooperating in a PD. They are spreading accurate reputational information, and probably also strengthening the social rewards system by increasing people’s expectations that good behavior will be socially rewarded or bad behavior will be socially punished. Even if these deathbed acts don’t benefit the individual, they arise from emotions that did benefit the individual (making others more likely to help them, or less likely to cheat them). And again, when these emotions were in development by natural selection, deathbed turn-off was probably a relatively low-priority feature to add (although there does seem to be some tendency for vindictiveness to get turned off when someone is dying—I’m not sure if that’s related).
Short answer: we’re adaptation executors, not fitness maximizers.
I fully get the point, but this doesn’t by itself explain why superior adaptations haven’t come along. Basically, we need to consider a “constraint on perfection” argument here, and ask what may be the constraints concerned in this case. It is generally possible to test the proposals.
Some obvious (standard) proposals are:
1) Mutations can’t arise to turn TFT into TFT-1
This is a bit unlikely for the reasons I already discussed. We do seem to have slightly different behaviour in the one-shot (or last-round) cases, so it is not implausible that some “mutant” would knock out co-operation completely on the last round (or on all rounds after a certain age—see my Grumpy-Old-Man idea above). There is a special concern when we allow for “cultural” mutations (or learned responses which can be imitated) as well as “biological” mutations.
2) Additional costs
The argument here is that TFT-1 has an additional cost penalty, because of the complexity overhead of successfully detecting the last round (or the only round), and the large negative cost of getting it wrong. Again it faces the objection that we do appear to behave slightly differently in last (or only) rounds, whereas if it were truly too difficult to discrimate, we’d have the same behaviour as on regular rounds.
3) Time-lags
This is the argument that we are adapted for an environment which has recently shifted, so cases of single-round (or known last-round) Prisoner’s Dilemma are much more common than before and evolution hasn’t caught up.
This might be testable by directly comparing behaviours of people living in conditions closer to Paleolithic versus industrialized conditions. Are there any differences in reactions when they are presented with one-shot prisoner’s dilemmas? If one-shot PD is a new phenomenon, then we might expect “Paleo-people” to instinctively co-operate, whereas westerners think a bit then defect (indicating that a learned response is overriding an instinctive response). This strikes me as somewhat unlikely (I think it’s more likely that the instinct is to defect, because there is a pattern-match to “not a member of my tribe”, whereas industrialized westerners have been conditioned to co-operate, at least some of the time). But it’s testable.
A variant of this is Randaly’s suggestion that true last-rounds are indeed new, because of the effect of retaliation against family (which has only recently been prohibited). This has a nice feature, that in cases where the last round truly was the last (because there was no family left), the mutant wouldn’t spread.
4) Side effects
Perhaps the mutations that would turn TFT into TFT-1 have other undesirable side effects? This is the counter-argument to Grumpy-Old-Man mutants invading because they have other positive side effects. Difficult to test this one until we know what range of mutations are possible (and whether we are considering biological or cultural ones).
Short answer: we’re adaptation executors, not fitness maximizers.
Isolated prisoners’ dilemmas were rare in the ancestral environment—most PD-like interactions took place in a social environment where they would (at least in expectation) have indirect effects either within a particular relationship or on one’s broader reputation (and thus shared features with an indefinitely iterated PD). So the advantages of being good at PD-in-a-social-context far outweighed the possible benefits of consistently defecting in the rare truly one-shot PD. That means most of evolution’s optimization power went towards building in adaptations that were good at PD-in-a-social-context, even if the adaptation made one less likely to defect in a truly one-shot PD.
For example, people tend to internalize their reputation, and to feel bad when others disapprove of them (either a particular close other or one’s broader reputation). Having a model of how others will react to your behavior, which is readily accessible and closely tied to your motivations, is very useful for PD-in-a-social-context, but it will make it harder to defect in a one-shot PD.
Another adaptation is the capability of feeling close to another individual, in such a way that you like & trust them and feel motivated to do things that help them. This adaptation probably involved repurposing the machinery that makes parents love their offspring (it involves the hormone Oxytocin), and it makes it harder to defect on the last turn. For actions towards one’s offspring, evolution didn’t want us to defect on the last turn. Adding last-turn defection in non-kin relationships seems like a lot of complexity for a low return, with a potentially high cost if the adaptation isn’t narrowly targeted and has collateral damage towards kin or earlier turns.
There are also various specific emotions which encourage TFT-like-behavior, like gratitude and vindictiveness. Someone who spends their last words on their deathbed praising the person who helped them, or cursing the person who cheated them, is cooperating in a PD. They are spreading accurate reputational information, and probably also strengthening the social rewards system by increasing people’s expectations that good behavior will be socially rewarded or bad behavior will be socially punished. Even if these deathbed acts don’t benefit the individual, they arise from emotions that did benefit the individual (making others more likely to help them, or less likely to cheat them). And again, when these emotions were in development by natural selection, deathbed turn-off was probably a relatively low-priority feature to add (although there does seem to be some tendency for vindictiveness to get turned off when someone is dying—I’m not sure if that’s related).
I fully get the point, but this doesn’t by itself explain why superior adaptations haven’t come along. Basically, we need to consider a “constraint on perfection” argument here, and ask what may be the constraints concerned in this case. It is generally possible to test the proposals.
Some obvious (standard) proposals are:
1) Mutations can’t arise to turn TFT into TFT-1
This is a bit unlikely for the reasons I already discussed. We do seem to have slightly different behaviour in the one-shot (or last-round) cases, so it is not implausible that some “mutant” would knock out co-operation completely on the last round (or on all rounds after a certain age—see my Grumpy-Old-Man idea above). There is a special concern when we allow for “cultural” mutations (or learned responses which can be imitated) as well as “biological” mutations.
2) Additional costs
The argument here is that TFT-1 has an additional cost penalty, because of the complexity overhead of successfully detecting the last round (or the only round), and the large negative cost of getting it wrong. Again it faces the objection that we do appear to behave slightly differently in last (or only) rounds, whereas if it were truly too difficult to discrimate, we’d have the same behaviour as on regular rounds.
3) Time-lags
This is the argument that we are adapted for an environment which has recently shifted, so cases of single-round (or known last-round) Prisoner’s Dilemma are much more common than before and evolution hasn’t caught up.
This might be testable by directly comparing behaviours of people living in conditions closer to Paleolithic versus industrialized conditions. Are there any differences in reactions when they are presented with one-shot prisoner’s dilemmas? If one-shot PD is a new phenomenon, then we might expect “Paleo-people” to instinctively co-operate, whereas westerners think a bit then defect (indicating that a learned response is overriding an instinctive response). This strikes me as somewhat unlikely (I think it’s more likely that the instinct is to defect, because there is a pattern-match to “not a member of my tribe”, whereas industrialized westerners have been conditioned to co-operate, at least some of the time). But it’s testable.
A variant of this is Randaly’s suggestion that true last-rounds are indeed new, because of the effect of retaliation against family (which has only recently been prohibited). This has a nice feature, that in cases where the last round truly was the last (because there was no family left), the mutant wouldn’t spread.
4) Side effects
Perhaps the mutations that would turn TFT into TFT-1 have other undesirable side effects? This is the counter-argument to Grumpy-Old-Man mutants invading because they have other positive side effects. Difficult to test this one until we know what range of mutations are possible (and whether we are considering biological or cultural ones).