This article, like most of Le Nguyen Hoang’s work, brings together a wonderful mix of ideas and resources and is mostly great. But I am a bit worried that it might leave some readers with the idea that kin selection and group selection are mutually exclusive alternatives when in fact I doubt that anyone in the “group selection” camp denies the importance of kin selection.
The “war” is I think between those who propose methods of group selection that are not explained by kinship and those who insist that everything can be explained by a concept of “inclusive fitness” defined in terms of kinship defined *only* by the family tree (and who also insist that nothing else can possibly happen).
With regard to what will eventually disappear, I don’t think there’s any chance that kin selection will disappear since everyone can see that it sometimes works. As for non-kin-based group selection, I can see ways it could work; and so, given the infinite inventiveness of nature, I am sure we will eventually identify examples where the pure-kin explanation does not suffice. So I like the article’s concluding reference to Max Plank. What will eventually disappear are those who are stuck on a currently favourite theory (only to be temporarily replaced of course by those who get stuck on the next one).
In Hamilton’s equation, whatever goes in as relatedness needs to be just the probability that the allele(s) for an A favouring a B are in fact carried by the B for whom the A is making the sacrifice.(eg the probability that child B of a parent A who guards its child will inherit and exhibit the same behaviour when it is a parent)
The definition of relatedness in terms of genomic similarity seems to be more general than kinship since although kinship would confer a predictable level of such relatedness I can imagine sharing an unusually high proportion of my genes with someone to whom I would neither have nor feel any particular level of family-tree-based “kinship”.
Either way, the issue of relationship-based altruism depends on the organism being able to recognize the relationship. For family-tree-based kinship that recognition may come mainly from experience, though I suppose there could be an element of “self-like” feature recognition in there also. But when it comes to genetic similarity it seems clear that only very small fraction of genes or gene complexes lead to recognizable features eg I may appear superficially more related to someone with the same skin colour but different blood type and other biochemical markers than to someone with all the same other markers and just a different skin colour. On the other hand, sharing a large number of alleles, as may be involved in a complex scent for example, may provide a useful stochastic proxy for kinship and so for overall relatedness, even when that number of alleles is much smaller than the total number of genes that vary in the population.
So far, what I have just said suggests that there is a plausible mechanism for the evolution of altruism based on kinship. But that is not disputed by anyone. The real question is whether there are any other plausible mechanisms for enhancing the probability that a B carries the allele(s) for altruistically favouring another (possibly unrelated) B when in role A.
And there are.
One is just for the selected behaviour to be “behave altruistically towards any beneficiary who has been seen to been consistently altruistic in the past”. If the level of altruistic sacrifice is determined by a suitable version of Hamilton’s equation with relatedness replaced by something to do with the predictability of genes from behaviour then the allele(s) for that kind of altruism will preferentially propagate. The allele(s) for unselective altruism may also get promoted but by being more altruistic it will incur greater costs and so presumably not take over.
(I am talking here as if the individuals are at a fairly high cognitive level but perhaps it doesn’t have to be so. Perhaps the behaviour could be something like “if you help me I put a bit of pheromone on you somewhere where you couldn’t do it yourself, and if I see an individual in distress I help if and only if I smell that pheromone in the designated spot”.)
Of course the effectiveness of this behaviour will depend on the capacity for recognizing consistency of altruism which may in turn depend on capacities for reputation management and multi-party interactions. It may also be effective to have defectors “punished” by more than just withdrawal of the benefits of altruism.
Here we are talking about a gene-complex for which some allele gives the capacity and tendency for recognizing and favouring non-related individuals who carry it and since this comes at the expense of other genes with whom this gene-for-altruism is travelling is could be said that the altruism gene is in fact the most selfish gene of all.
So far I have talked about non-kin-based selection but I haven’t yet said anything about group selection at all. For that we need to look at competition between groups.
If the population lives in a context where the altruistic behaviour enables better overall use of resources, then groups where it arises will flourish more than those where it does not. But if all members of each group are related then perhaps even if kinship does not explain everything about the distribution of characteristics within a group it may do so for the competition between groups. (After all if a cooperating group of relatives whose members all happened to carry a mutation which made them bigger and stronger beat out another group of the same species we probably wouldn’t say that represented a new phenomenon beyond the predictions of kin selection).
So for an example of group selection that is not just a special case of kin selection we probably need to envisage a situation where the groups are not defined solely by kinship but rather, at least in part, by the joining and cooperation of unrelated individuals.
In such a context, groups with members who are good at recognizing and adopting cooperative outsiders may out-compete other groups. If the capacity for enhancing the group’s success in this way comes at some cost to the success of the individual within the group (so that without inter-group competition the allele for that capacity would actually die out over time), then the survival and propagation of that capacity really is due to group selection and not to anything about favouring actual relatives.
And of course, in a world covered with competing groups of the same thriving species there may be other less attractive behaviours selected for as well.