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Comment by rcthompson | Hacker News Reader

I'm a biologist, and I never realized that group selection wasn't broadly accepted until I read this article. I'd always assumed it was trivially implied by the theory of natural selection. Natural selection has been observed at every level, from entire organisms all the way down to the subcellular level (transposable elements, mitochondria, and others) I've never doubted that it also operates on populations of organisms.

I've often explained aspects of human society to my non-scientist friends in terms of group selection. (Short version: Humans who formed tribes out-competed the loners.)

On an unrelated note, I don't see how group selection and kin selection are mutually exclusive.

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It appears you may have been misinformed.

Kin selection: organism X helps organism Y because it improves the prospects for the part of X's DNA that Y also has. The more related X is to something, the more willing X is to sacrifice itself for it. The most extreme example is also the most familiar: each of your cells has DNA identical to each of your other cells (if all is well). So a cell is completely willing to kill itself for the "collective", even at the expense of its own ability to reproduce. A less extreme example is that of a woman declining to pursue kids of her own in order to help tend her sister's, which could be adaptive when, e.g., food is scarce.

Group selection: members of a particular group (e.g., a tribe) are willing to engage in altruistic actions (e.g., suicidal defense of said tribe pre-procreation) even though doing so maladaptive at the level of the individual's DNA. This kind of cooperation is adaptive for the group as a whole, but not in the least for the individual. Groups that encourage this kind of behavior will outcompete groups that don't, so groups are selected for this trait.

IIRC, the primary reason that group selection is thought to be wrong is that it (apparently) can't yield an Evolutionarily Stable Strategy (ESS) -- it will always be better for the persistence of any individual's DNA if that individual refuses to be altruistic.

"IIRC, the primary reason that group selection is thought to be wrong is that it (apparently) can't yield an Evolutionarily Stable Strategy (ESS) -- it will always be better for the persistence of any individual's DNA if that individual refuses to be altruistic."

This sounds reasonable if you consider only one generation, or only the individual. But if you consider the whole group or species in the long run, the effect you see is exactly what you describe, i.e. groups that encourage this kind of behavior will outcompete groups that don't. So for a species to survive, it is much more important that the group survives than just an individual. If the individual survives, but it can't reproduce, then the species won't survive in the long term.

I think the important thing is to determine what behavior better represents reality, meaning what would explain the survival of current species on earth, not just try to confirm survival of the fittest for an individual.

>IIRC, the primary reason that group selection is thought to be wrong is that it (apparently) can't yield an Evolutionarily Stable Strategy (ESS) -- it will always be better for the persistence of any individual's DNA if that individual refuses to be altruistic.

I don't think that could be right, because the altruistic individuals altruism could include killing/punishing non-altruistic individuals. Shooting deserters comes to mind, as a real-life human example.

> IIRC, the primary reason that group selection is thought to be wrong is that it (apparently) can't yield an Evolutionarily Stable Strategy (ESS) -- it will always be better for the persistence of any individual's DNA if that individual refuses to be altruistic.

"always will be better" seems to assume that group viability has no effect on individual survival.

While it's best to be the most selfish in the group, that doesn't imply that it's good enough. You need to also survive, and some groups help with that by having some altruism.

Re exclusivity: The article portrayed it as a debate over which one is the cause. Does group altruism exist because we desire to help kin, or does kin altruism exist *because we desire to help the group?

Group selection sounds more reasonable (by being more easily implementable at a sub-conscious level) to me.

I think what rcthompson was asking is why can't both kin altruism and group altruism exist as primary causes? If there's a genetic (as opposed to memetic) basis, it's conceivable* that there is a single gene that, if mutated, would cause individuals to care about the group, but not direct kin any more than the group at large, or to care about close kin, but not the larger group. Given how much of biology is layers of overlapping, cooperative systems, I would guess this is the most likely idea: that both kin selection and group selection are active, to varying degrees in different populations.

* Though unlikely

Yes, that's what I meant: I don't see why either one has to be the cause of the other.

What does it mean to say that natural selection is observed at the level of an organism? I'm not a biologist, but I was under the impression that natural selection on all of the 'levels' of biology all shook out to being natural selection of snippets of DNA.

Natural selection at the level of organisms is just the "regular" form of evolution that we are familiar with. I used the word "organism" simply as a contrast to other levels at which natural selection can act.

Note that although the DNA is the genetic material, a selective pressure such as the threat of predation acts on organisms. Very rarely would selection act directly on the DNA. Rather, the correlation between carrying a snippet of DNA and not getting eaten causes that snippet to become overrepresented in the population over time.

Got it, thank you. I'd love to see a good pointer to worked out examples of natural selection happening at non-organism levels if you have one handy. It sounds pretty fascinating.

Well, one of the best cell-level examples I can think of is somatic hypermutation, the mechanism by which your immune system refines a good antibody into an excellent one. Briefly, your body starts out with the B-cell that produces the good antibody, and randomly mutates the critical regions of the antibody gene, generating a large population of B-cells that each produce slightly different antibodies. The B-cells with the best antibodies (highest affinity for the antigen) are selected and given the "do not die" signal. The rest of the B-cells do not receive this signal and self-destruct. The end result is a population of B-cells that produce higher-affinity antibodies than the original. Repeat while ill.

I may misremember some of the details, but that's the gist. Your body basically generates antibodies via an evolutionary algorithm. Wikipedia has a good explanation. Keep an eye out for the word "selection": http://en.wikipedia.org/wiki/Somatic_hypermutation

Hey, look at that. Wikipedia also has this enlightening article: http://en.wikipedia.org/wiki/Unit_of_selection

Wow. That is nothing short of amazing. Thank you, your comment motivates me to learn more about biology. For one, I have been labouring under the illusion that the brain holds a monopoly in terms of organizing intelligent behaviour. The immune system is clearly another. Got any more examples?

This suggests that it takes a complex organism to fight disease. Once multicell organisms developed do you think an immune system was the first type of organized intelligence or that foreign invaders and parasites served as a catalyst to ever more complex systems?

It doesn't necessarily take a complex organism to fight disease. Pretty much every organism, including unicellular ones such as bacteria, possesses some form of innate immunity against that organism's most common pathogens. Simpler organisms fight disease by simply reproducing faster than the disease can kill them.

As for the brain having some sort of monopoly on "organizing intelligent bahavior", that is a complex issue. I wouldn't say that the adaptive immune system necessarily possesses intelligence. It consists of many small and relatively simple components that interact to produce complex behavior. Realize that during somatic hypermutation, the immune system is not intelligently choosing which mutations to generate. It simply generates a random sample of all possible mutations and then sets up a simple selection process that produces a result that looks intelligent to us.

On the other hand, one could plausibly make a similar argument about the brain's intelligence being the product of the interaction of individual neurons. Many people believe that our brains are no less deterministic than a silicon-based computer. Complexity is complex.

Anyway, to give you another example, cancer cells are subject to greatly increased mutation rates, and mutations that result in faster growth or better recruitment of nutrient-supplying blood vessels (vascularization) will quickly become fixed in the tumor as the cells with that mutation overtake the growth of others. This also provides an example where selection at the cellular level is at conflict with selection at the organismal level. Within the tumor, selection favors faster-growing cancer cells, but these same cells are clearly the most detrimental to the organism as a whole.

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