You are correct in saying that TFT cannot strictly evolve (starting with 0 population) from TFT-nD in that case. However, for increasing n and number of rounds the extinction threshold becomes sufficiently small. Maybe more importantly, unlike in the type of tournaments discussed in the link, real people can identify other people outside the game. There’s nothing to stop a player from playing different strategies depending on which group of people the other player belongs to. If we assume a prehistoric tribe where people defect a lot, just two players cooperating with each other for a little longer than the others have found a winning strategy already. In addition to that, it also becomes attractive for other players to join their little clique.
Basically, this leads us to a form of meta-TFT—”If you defect first in interpersonal interaction, you are not in our little group of cooperators anymore.” So in a tribe of people who know each other and need to interact with certain other people within that tribe, cooperation is the winning strategy for everyone. Inter-tribe competition amplifies this.
The larger the tribe and the easier it is to leave the tribe, the smaller the benefits of cooperation become. But even in modern society most people are part of such tribe-like groups where they are forced or have sufficient motivation to interact with certain other people—family, kindergarten, school, workplace, clubs, whatever. People learn to achieve their goals within these groups from a very young age by forming cliques, so TFT-like strategies are naturally adopted.
Thanks for acknowledging that there is an issue here, and something worth explaining. Upvoted.
Your suggested explanation for how TFT invades TFT-nD requires something more than just TFT here. As well as a cluster entry (at least two initially, not just one mutant), it also requires an ability to select preferred partners (i.e. the two co-operators preferentially select each other), and a reputational system (to help decide which partners to select).
This raises a question which could be tested: do all species that engage in reciprocal altruism have those additional features i.e. preferred partners and reputation? Do vampire bats? (It seems quite an overhead for a bat, doesn’t it?) Can TFT plausibly invade with fewer features?
Another concern would be how TFT enters a population of DefectBots in the first place… It would require a major (and implausible) mutation to introduce all these features at once. Even TFT by itself (without the extra features) is significantly more complicated than a DefectBot, which raises an origin question : what series of mutations can put TFT together starting from a DefectBot, and how are the intermediates favoured? Does machinery for kin selection need to evolve first and then get re-purposed? (This leads to another prediction, that reciprocating species also have to practice kin selection, or at least have ancestors which did).
I disagree with you that defecting is the default action for animals in state/herd/pack/tribe-like communities. Unless you want to discuss how these kind of communities could form in the first place, it seems to me that the question how TFT can prohibit TFT-nD from invading is much more relevant than how TFT can invade TFT-nD. And that is ultimately the point—as I’ve explained above, for a tribe-forming species TFT (or meta-TFT) is an evolutionary stable strategy.
I disagree with you that defecting is the default action for animals in state/herd/pack/tribe-like communities. Unless you want to discuss how these kind of communities could form in the first place,
Are you claiming here that all herd or pack species are practising TFT, or that it is the default for herd/pack species? That seems empirically dubious: my understanding was that herd or pack species are mainly held together either by kin selection (the pack consists of close relatives) or by simple mutualism (e.g. being in the herd protects against predation, and it would be suicide to leave) rather than by something as sophisticated as TFT. It’s a while since I looked at the literature, but species practising reciprocal altruism with non-relatives seem to be fairly rare. But if you can cite studies, that would be helpful.
You are correct in saying that TFT cannot strictly evolve (starting with 0 population) from TFT-nD in that case. However, for increasing n and number of rounds the extinction threshold becomes sufficiently small. Maybe more importantly, unlike in the type of tournaments discussed in the link, real people can identify other people outside the game. There’s nothing to stop a player from playing different strategies depending on which group of people the other player belongs to. If we assume a prehistoric tribe where people defect a lot, just two players cooperating with each other for a little longer than the others have found a winning strategy already. In addition to that, it also becomes attractive for other players to join their little clique.
Basically, this leads us to a form of meta-TFT—”If you defect first in interpersonal interaction, you are not in our little group of cooperators anymore.” So in a tribe of people who know each other and need to interact with certain other people within that tribe, cooperation is the winning strategy for everyone. Inter-tribe competition amplifies this.
The larger the tribe and the easier it is to leave the tribe, the smaller the benefits of cooperation become. But even in modern society most people are part of such tribe-like groups where they are forced or have sufficient motivation to interact with certain other people—family, kindergarten, school, workplace, clubs, whatever. People learn to achieve their goals within these groups from a very young age by forming cliques, so TFT-like strategies are naturally adopted.
Thanks for acknowledging that there is an issue here, and something worth explaining. Upvoted.
Your suggested explanation for how TFT invades TFT-nD requires something more than just TFT here. As well as a cluster entry (at least two initially, not just one mutant), it also requires an ability to select preferred partners (i.e. the two co-operators preferentially select each other), and a reputational system (to help decide which partners to select).
This raises a question which could be tested: do all species that engage in reciprocal altruism have those additional features i.e. preferred partners and reputation? Do vampire bats? (It seems quite an overhead for a bat, doesn’t it?) Can TFT plausibly invade with fewer features?
Another concern would be how TFT enters a population of DefectBots in the first place… It would require a major (and implausible) mutation to introduce all these features at once. Even TFT by itself (without the extra features) is significantly more complicated than a DefectBot, which raises an origin question : what series of mutations can put TFT together starting from a DefectBot, and how are the intermediates favoured? Does machinery for kin selection need to evolve first and then get re-purposed? (This leads to another prediction, that reciprocating species also have to practice kin selection, or at least have ancestors which did).
I disagree with you that defecting is the default action for animals in state/herd/pack/tribe-like communities. Unless you want to discuss how these kind of communities could form in the first place, it seems to me that the question how TFT can prohibit TFT-nD from invading is much more relevant than how TFT can invade TFT-nD. And that is ultimately the point—as I’ve explained above, for a tribe-forming species TFT (or meta-TFT) is an evolutionary stable strategy.
Are you claiming here that all herd or pack species are practising TFT, or that it is the default for herd/pack species? That seems empirically dubious: my understanding was that herd or pack species are mainly held together either by kin selection (the pack consists of close relatives) or by simple mutualism (e.g. being in the herd protects against predation, and it would be suicide to leave) rather than by something as sophisticated as TFT. It’s a while since I looked at the literature, but species practising reciprocal altruism with non-relatives seem to be fairly rare. But if you can cite studies, that would be helpful.