The difficulty with this explanation is that humans can (often) recognize when “this time is the last”, and the computational cost of doing something different in that case is not great.
Biological altruism is not unique to humans; other animals, whose adaptations for altruism, are presumably much worse at conscious considerations of this kind. In addition, the common nature of one-shot PD-esque encounters, where you’ll never see the other player again, is in many ways a unique byproduct of the modern world, meaning that there would be little selection pressure for an adaption that defects on the last round.
And we often change our behaviour radically when we know we are going to die soon, but this change rarely involves antisocial behaviour like stealing, mugging, running up huge debts we’ll never have to pay back and so on.
Evolutionarily speaking, what matters is the genes; even after a person dies, their foes can retaliate against their kids.
But there is a major problem with this story: the “emotionally committed” ancestors could be out-competed in turn by bluffers. Anyone who could fake the emotional signals would be able to elicit the benefits of co-operation (they would successfully deter defection), but without having to follow through on the (costly) commitments in case the co-operation failed. Bluffing out-competes commitment.
This is a strictly theoretical response; empirically, it appears that people are willing to punish defectors, even at cost to themselves. (There are a couple of ways around the theoretical objection; one is that anybody who failed to punish would immediately become a target for defection in future rounds or by other people; another is that it’s possible that the social group (or tribe or whatever) would join in the punishment, or even punish non-punishers, in order to prevent defection. I have no evidence whatsoever for either of these possible mechanisms, and do not strongly believe in either or them.)
But a more basic objection is “How did we ever get into a social environment where third party reputation matters like this?” Consider for instance a small society involving Anne, Bob, and Charles. Anne and Bob are engaging in an iterated prisoners’ dilemma, and regularly co-operating. Bob and Charles meet in a one-shot prisoners’ dilemma, and Bob defects. Anne sees this. How does it help Anne in this situation to start defecting against Bob? Generally it doesn’t. A reputational system only helps if it identifies and isolates people who won’t co-operate at all (the pure defectors). But Bob is not a pure defector, so why does he end up being penalized by Anne?
I feel like this abstracts too far away from reality. Nobody is actually a pure defector or pure cooperator; their decision to defect or not to defect against one person provides evidence to others about how likely/under what circumstances they will defect.
Biological altruism is not unique to humans; other animals, whose adaptations for altruism, are presumably much worse at conscious considerations of this kind. In addition, the common nature of one-shot PD-esque encounters, where you’ll never see the other player again, is in many ways a unique byproduct of the modern world, meaning that there would be little selection pressure for an adaption that defects on the last round.
Note that I did discuss an argument like this (such that the variant which defects on the last round is more complicated, and the last round or single-round case happens rarely enough that it can’t be selected for). But it strikes me as implausible, particularly for human beings. There’s something “off” with the theory of reciprocal altruism if it relies on that defence against last round defection : the prediction would be that the cleverer the species, then the more likely they are to detect last-round cases, and the more likely reciprocal altruism is to collapse over time. So we would see less reciprocal altruism in cleverer species, but the opposite is true.
Incidentally, we could try to test the theory in vampire bats (also known to practice reciprocal altruism). Do bats stop reciprocating after a certain age (because death now too close)? Is there any selection pressure for that age to slowly creep forwards in a given population to younger and younger ages? If so, is there a counter-pressure which stops the creep forward, and what is it?
Evolutionarily speaking, what matters is the genes; even after a person dies, their foes can retaliate against their kids.
Yes, that’s theoretically sound i.e. this could stop last-round defection ever entering the population. Again it could be tested in vampire bats and other reciprocating species.
It’s kind of a grizzly thought though, isn’t it? That reciprocal altruism is maintained by vengeance against a whole family… It suggests that cultures which taboo such vengeance will eventually collapse (from last round defection creeping forwards), but there’s no evidence of that as far as I can see. Perhaps the taboo is too recent, and the effect hasn’t set in yet.
Yes, that’s theoretically sound i.e. this could stop last-round defection ever entering the population. Again it could be tested in vampire bats and other reciprocating species.
Well, we know that a fair number of historical human legal systems allowed the sins of the father to be visited on their children:
In Japan, Samurai revenge killings could also kill the perpetrator’s family.
In Afghanistan, the cultural practice of using daughters as currency to settle disputes of their relatives is called baad; the girl is then typically abused. (I am assuming that, since they are being treated as property, they can be confiscated after death to settle debts just like any other property.)
In Hinduism the Laws of Manu (4-173) state that “If (the punishment falls) not on (the offender) himself, (it falls) on his sons, if not on the sons, (at least) on his grandson.”
A few, disorganized notes:
Biological altruism is not unique to humans; other animals, whose adaptations for altruism, are presumably much worse at conscious considerations of this kind. In addition, the common nature of one-shot PD-esque encounters, where you’ll never see the other player again, is in many ways a unique byproduct of the modern world, meaning that there would be little selection pressure for an adaption that defects on the last round.
Evolutionarily speaking, what matters is the genes; even after a person dies, their foes can retaliate against their kids.
This is a strictly theoretical response; empirically, it appears that people are willing to punish defectors, even at cost to themselves. (There are a couple of ways around the theoretical objection; one is that anybody who failed to punish would immediately become a target for defection in future rounds or by other people; another is that it’s possible that the social group (or tribe or whatever) would join in the punishment, or even punish non-punishers, in order to prevent defection. I have no evidence whatsoever for either of these possible mechanisms, and do not strongly believe in either or them.)
I feel like this abstracts too far away from reality. Nobody is actually a pure defector or pure cooperator; their decision to defect or not to defect against one person provides evidence to others about how likely/under what circumstances they will defect.
Note that I did discuss an argument like this (such that the variant which defects on the last round is more complicated, and the last round or single-round case happens rarely enough that it can’t be selected for). But it strikes me as implausible, particularly for human beings. There’s something “off” with the theory of reciprocal altruism if it relies on that defence against last round defection : the prediction would be that the cleverer the species, then the more likely they are to detect last-round cases, and the more likely reciprocal altruism is to collapse over time. So we would see less reciprocal altruism in cleverer species, but the opposite is true.
Incidentally, we could try to test the theory in vampire bats (also known to practice reciprocal altruism). Do bats stop reciprocating after a certain age (because death now too close)? Is there any selection pressure for that age to slowly creep forwards in a given population to younger and younger ages? If so, is there a counter-pressure which stops the creep forward, and what is it?
Yes, that’s theoretically sound i.e. this could stop last-round defection ever entering the population. Again it could be tested in vampire bats and other reciprocating species.
It’s kind of a grizzly thought though, isn’t it? That reciprocal altruism is maintained by vengeance against a whole family… It suggests that cultures which taboo such vengeance will eventually collapse (from last round defection creeping forwards), but there’s no evidence of that as far as I can see. Perhaps the taboo is too recent, and the effect hasn’t set in yet.
OK
Well, we know that a fair number of historical human legal systems allowed the sins of the father to be visited on their children:
In Japan, Samurai revenge killings could also kill the perpetrator’s family.
In the Bible/Torah, while humans are banned from killing a son for the sins of his father, it’s also stated that God will punish the next four generators for the sins of one person. (It’s also suggestive that they needed to ban killing the son for the sins of the father.)
In Afghanistan, the cultural practice of using daughters as currency to settle disputes of their relatives is called baad; the girl is then typically abused. (I am assuming that, since they are being treated as property, they can be confiscated after death to settle debts just like any other property.)
In Hinduism the Laws of Manu (4-173) state that “If (the punishment falls) not on (the offender) himself, (it falls) on his sons, if not on the sons, (at least) on his grandson.”
The Taoist Treatise on Response and Retribution states that “If at death an unexpiated offence be left, the evil luck will be transferred to children and grandchildren. Moreover, all those who wrongly seize others’ property may have to compensate for it, with wives or children or other family members, the expiation to be proportionate up to a punishment by death.”
(As an aside, thank you for your fantastically well-written and well-thought out comment.)