Group selection update
Group selection might seem like an odd topic for a LessWrong post. Yet a google seach for “group selection” site:lesswrong.com turns up 345 results.
Just the power and generality of the concept of evolution is enough to justify posts on it here. In addition, the impact group selection could have on the analysis of social structure, government, politics, and the architecture of self-modifying artificial intelligences is hard to over-estimate. David Sloan Wilson wrote that “group selection is arguably the single most important concept for understanding the nature of politics from an evolutionary perspective.” (You should read his complete article here—it’s a much more thorough debunking of the debunking of group selection than this post, although I’m not convinced his interpretation of kin selection is sensible.) And I will argue that it has particular relevance to the study of rationality.
Eliezer’s earlier post The Tragedy of Group Selectionism dismisses group selection, based on a mathematical model by Henry Harpending and Alan Rogers. That model is, however, fatally flawed: It studies the fixation of altruistic vs. selfish genes within groups of fixed size. The groups never go extinct. But group selection happens when groups are selected against. The math used to argue against group selection assumes from the outset that group selection does not occur. (This is also true of Maynard Smith’s famous haystack model.)
(That post is still valuable; its main purpose is to argue that math trumps wishes and aesthetics. Empirical data, however, trumps mathematical models.)
Nitpicking digression on definitions
“Group selection” is one of those tricky phrases that doesn’t mean what it means. Denotationally, group selectiond means selection at the level of a group. Connotationally, though, group selectionc means selection for altruistic genes at the level of a group. This is because, historically, group selection was posited to explain genetic adaptations that are hard to explain using individual selection.
group selectionn, selection at the group level for traits that are neutral or harmful at the level of the individual, or that don’t even exist within the individual genome, should also be considered. group selectionc is a subset of group selectionn is a subset of group selectiond. If group-level selection occurs at all, then traits of the group that are not genetic traits, including cultural knowledge, must be considered. That makes a huge difference. Human history is full of group selectionn. Every time one group with better technology or social organization pushes another group off of its land, that’s at least group selectionn.
If you want to model evolution thoroughly, and selection of groups occurs, then you need to model group selectiond to get your predictions to match reality, even if group selection occurs entirely as a result of non-group selectionc genetic traits that provide advantages to individuals. But people reject group selectiond on the basis of arguments leveled against group selectionc.
A case study of group selectionc: Nightshades
But I’m not backing off from saying that group selection can explain (some) altruism. Edward Wilson has been threatening for several years to write a book showing that group selection is more important than kin selection for generating altruism in ants. He doesn’t seem to have published the book, but you can read his article about it. (Short version: Group selection is especially important in ants because ant colonies, which are small groups, engage in constant warfare with each other.)
And this brings me to the reason for writing this post now. Last week’s Science contained an article by Emma Goldberg et al. with the most clear-cut demonstration of group selection that I have yet seen (summarized here). It concerns flowering plants of the nightshade family (Solanaceae). They descend from plants that evolved self-incompatibility (SI) about 90 million years ago. SI plants can’t pollinate themselves. This is a puzzling trait. Sexual reproduction in itself is puzzling enough; but once a species is sexual, individual selection should drive out SI in favor of self-compatibility (SC), the ability to self-pollinate. SC gives individuals a great reproductive advantage—it means their offspring can contain 100% of their genes, rather than only 50%. The advantage given by SC is much greater than the supposed advantage of asexual over sexual reproduction: SC plants can both leave their own cloned offspring, and foist their genes onto the offspring of their neighbors at no additional cost to themselves. SC also makes survival of their genes much more likely when a single plant is isolated far from others of its species; this, in turn, makes spreading over geographical areas easier.
And yet, SI is a complex, multi-gene mechanism that evolved to prevent SC. Why did it evolve?
The authors looked at a phylogenetic tree of 998 species of Solanaceae. In this tree, SI keeps devolving into SC. Being an SC mutant in an SI species is the best of both worlds. You get to pollinate yourself, and exploit your altruistic SI neighbors. When some members of an SI species go SC, we expect those SC genes to eventually become fixed. And once a Solanaceae species loses SI and becomes SC, it never re-evolves SI. This has been going on for 36 million years. So why are so many species of Solanaceae still SI?
Let sI = speciation rate for SI; eI = extinction rate for SI; rI = net rate of species diversification = sI—eI. Likewise, rC is the net rate of species diversification for SC species. qIC is the rate of transition from SI to SC. SI will be lost completely if sI—eI = rI < rC + qIC = (sC—eC) + qIC.
The data shows that sC > sI, but eC >> eI, enough so that rI > rC + qIC. In English: Self-pollinators speciate and diversify more rapidly than SI species do, as we expect because SC provides an individual advantage. Once self-pollinators evolve in an SI species, these exploiters out-compete their altruistic SI neighbors until the entire species becomes SC. However, SC species go extinct more often than SI species. This is thought to be because SI makes a species less-likely to fixate deleterious genes (makes it more evolvable, in other words). Individual selection favors SC; but species selection favors SI more than enough to balance this out. Notice that gene-based group selection at the species level is mathematically more difficult than group selection at the tribal (or ant colony) level (ADDED: unless there is genetic flow between groups at the tribal/colony level).
So let’s stop “accusing” people of invoking group selection. Group selection is real.
Group rationality
Group selection is especially relevant to rationality because, in an evolving system, if we use the definition “Rationalists win,” “winning” applies to the unit of selection. In my painfully long post Only humans can have human values, the sections “Instincts, algorithms, preferences, and beliefs are artificial categories” and “Bias, heuristic, or preference?” argue that the boundary between an organism’s biases and values is an artificial analytic distinction. Similarly, if group selection happens in people, then our discussion of rationality and values is overly focused on the rationality and values of individuals, when group dynamics are part of what produces rational (winning) group behavior.
Even if you still don’t believe in group selectionc, you should accept that group selectionn may allow information to drift back and forth, in a fitness-neutral way, from being stored in genomes, to being culturally transmitted. And that makes it necessary, when talking about rationality in a normative way, to consider the rationality of the group, and not just the rationality of its individuals.
(This is related to my unpopular essay Rationalists lose when others choose. When the unit of selection is the group, rather than the individual, the “choice” is made on the basis of benefit to the group, rather than benefit to the individual. This will prefer “irrational” individuals who terminally (perhaps unconsciously) value benefits to the group, and not just benefits to themselves, over “rational” self-interest.)
group selectionn makes the Prisoner’s Dilemma and tragedies of the commons smaller problems. But it raises a new problem: Is the individual the wrong place to put some of our collective rationality? Since humans have evolved in groups for a long time, the default assumption is that attributes, such as our rationality, are already optimized for the unit of selection.
Less generally, if the group has already evolved to place some of our rationality into the group, what will happen if we try to instill it into the individuals? Since group selection is real, we can expect to find situations where making individuals more rational upsets the evolutionary equilibrium and makes the group win less. Under what circumstances will making individuals more rational interact badly with group dynamics, and make our group less rational (= win less)? This will probably occur in circumstances involving individual altruism. But if the locus of group rationality can drift from individual genes to cultural knowledge, it may also occur in situations not involving altruism.
Postscript: The long-term necessity of war
If group selection is partly responsible for human altruism, this means that world peace may increase selfishness. Konrad Lorenz made a subset of this claim in On Aggression (1966): He claimed that the more effective each individual’s killing tools are, the more necessary empathy is, to keep members of the group from killing each other; then invoked group selection. (This seems to me to apply a lot to canines and not much to felines.) If group selection works best with small groups, the switch from tribes to nation-states may have already begun this process. I do not, however, notice markedly greater altruism in tribal groups than in nation-states.
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The cited article is about species selection—but this post claims to be about group selection.
As biologists often use the terms, group selection and species selection are quite different concepts.
The standard objection to group selection—which is that gene transfer due to between-group migration and recombination usually swamps the effect of between-group selection—doesn’t apply to selection between species—because there is little or no gene transfer between species.
As a result, species selection isn’t very controversial—compared to group selection.
Group selection has been demonstrated in the lab (Wade’s flour beetles, etc) - but there is still some controversy over its significance in nature.
Yes, species are groups—but the actual area where there is a controversy is over selection between groups that are within sexual species. Selection between species is not relevant to this.
However, I agree that articles like this make EY look as though he has wandered into an unfamiliar area—which he doesn’t know as much about as he thinks he does.
I’ve just spent 2 hours sorting through various references to group selection to try to figure out whether your distinction is correct. As Samir Okasha writes, “The group selection debate has been characterised by perennial disagreements over concepts and terminology, as well as empirical fact.”
So far, Stephen J. Gould uses this group/species distinction, and almost everyone else rejects it. The more common usage is given in the BioTech Life Science Dictionary:
(Gould uses the term interdemic selection, but says it is synonymous with group selection, and distinguishes it from species selection.)
Eliezer’s post talked about species selection. David Wilson’s 2009 blog series on group selection, Truth & Reconciliation (linked to in the post), says nothing about any distinction between “group selection” and “species selection”; and the endangered bird species example of group selection in part 18 (p. 39) is species selection. Read the Wikipedia entry on group selection—everything that it says applies to species selection. All of the arguments presented against group selection apply equally to species selection. Some of the instances of group selection it provides are species selection. It never draws any distinction between group selection and species selection.
Many examples in various sources of group selection do not have between-group migration, and do have extinction of groups. For example, the ant colonies that EO Wilson talks about—there is AFAIK no gene transfer between ant colonies, since ants can’t migrate from one colony to another. On the Wikipedia page on group selection, it includes as examples viruses in rabbits, where selection occurs at the level of a single rabbit, and no gene transfer occurs between different infected rabbits.The Rauch et al analysis referred to is a similar case. So is the “brain worm” example.
Many attacks on group selection, including Williams’ Adaptation and Natural Selection (1966), speak in general terms about selection at higher levels indiscriminately, not singling out group vs. species selection. Here is what Richard Dawkins writes when attacking group selection in The Selfish Gene:
Here is a quote from Samir Okasha (2005), Maynard Smith on the levels of selection question:
So, George Williams, John Maynard Smith, Richard Dawkins, and David Wilson all agree that group selection includes species selection.
Maynard Smith’s haystack model, which was the original theoretical basis for rejecting group selection (and is fatally flawed; see p. 17 of the David Wilson T&R essay), does not work on species selection. The mathematical model that Eliezer used does not apply to species selection (nor to interdemic selection in general). Yet they use the phrase “group selection”. So there is some basis for considering group selection to be synonymous with interdemic selection; but that basis appears to be the carelessness of earlier theorists.
The group-selection-bashing I’ve witnessed for decades has always taken the line that all group selection, including species selection, is equally bad. I’ve seen many people object to the invocation of group selection, and I’ve never noticed any of them draw a distinction between interdemic and species selection.
Please cite a reference for your usage of the terms.
Richard Dawkins wrote an obituary for George Williams in the Oct. 1 Science, in which he said that Williams developed the idea of “clade selection” which Dawkins calls important. Clade selection is the idea that selection can operate on an entire clade.
The article this post is about a clade. It’s clade selection in that the entire clade has benefitted from SI. Is it also species selection, because entire species are selected against when they develop SC? I think so.
In either case, I think it’s hypocritical of Dawkins to call group selection “loose, intellectually shoddy.. muddled”, and in the same article praise clade selection.
Rather than calling Dawkins a hypocrite, don’t you think it would be more appropriate to simply note that Dawkins seems to be another person who doesn’t agree with you that clade selection (and hence species selection) is just one form of group selection?
Obituary: George C. Williams (1926–2010) - By RICHARD DAWKINS
Wikipedia gives an acceptable definition:
http://en.wikipedia.org/wiki/Group_selection
In the context of biology or ecology, a “population” is defined as being a collection of organisms of the same species:
http://en.wikipedia.org/wiki/Population
http://www.talktalk.co.uk/reference/encyclopaedia/hutchinson/m0015159.html
http://wordnetweb.princeton.edu/perl/webwn?s=population
For examples of group selection critics being more sympathetic towards species selection, see Dawkins, T.E.P., page 101 onwards and Mark Ridley’s evolution textbook:
http://www.blackwellpublishing.com/ridley/a-z/Group_selection_.asp
http://www.blackwellpublishing.com/ridley/a-z/Species_selection.asp
For a different definition, consider:
http://www.clarku.edu/faculty/nthompson/Publish%20Work/meta4grp.pdf
That wasn’t my greatest reply ever—I was in a rush. Yes, Dawkins included species in your quote. And Williams (1966) defined the term “group” in a way that didn’t explicitly rule out species. So, I agree that some prominent folks have included species under the group selection umbrella at least once.
However, at least 90% of group selection models deal with sexual species. If you claim group selection exists, and then exhibit species selection to prove it, an awful lot of evolutionary biologists are going to say: “well, that’s just species selection—we already know about that”.
Interdemic selection has a problem not found in species selection—namely gene flow typically tends to quickly destroy variation between groups. It is that that effect that Maynard-Smith modelled in the material you cite—and it is interdemic selection which is the most controversial.
A species is a collection of organisms of the same species.
A family is a collection of organisms of the same species (although I have my doubts about that aunt...)
Your point is not clear to me.
If you define a species as the set of all such organisms, then a “population” is a subset of that set.
And a set is a subset of itself.
I don’t really see where you are going with this. Yes, all the members of a species could qualify as being a “population”—expecially if they all lived in the same place.
However, that doesn’t make species selection into a special case of group selection under the Wikipedia definition.
Wikipedia seems to contradict this: “It remains controversial among biologists whether selection can operate at and above the level of species.”
I did a quick search on Google and found a paper from 2010 which claims that “Species selection as a potential driver of macroevolutionary trends has been relegated to a largely philosophical position in modern evolutionary biology.”
I’m not very familiar with biology, but at a glance it looks like species selection is pretty controversial.
That seems to be a rather confused way of putting it. Or course selection operates between species. The issue is whether it results in very much in the way of species-level adaptations.
Did you read the whole abstract? They say “species selection is an important process”:
I did read the whole abstract: the author admits that species selection is controversial in modern evolutionary biology, and in the rest of the paper argues that this should not be the case. The point of my previous comment was not whether species selection should or should not be recognized as important, because I do not know. It was a question concerning how well-accepted species selection is amongst biologists.
That may be so. If so, I am misusing the terminology. But if so, other people routinely use the objection to what you are calling “group selection” to rebut invocations of what you are calling “species selection”.
Hmm—I am not sure I have encountered that. Many definitions of “species” are based on there being little or no gene flow between different species.
Both group selection and species selection face the issue of the fact that reproduction rates are slow—compared to individual reproduction rates—so individual level selection could eliminate much of the variation on which higher-level selection could act.
However, with species selection, we know that species do eventually diverge—so there is some variation left to work on.
With group selection there’s less evidence of divergence between groups—and there’s an additional problem—that occasional gene flow between groups acts to reduce between-group differences. The math[*] suggests around 1 migrant per-generation is enough to make most group selection pretty ineffective—and 1 migrant per-generation is low for most natural groups. These factors are mainly what makes group selection more controversial.
Search for “One-Migrant-per-Generation Rule” for more on this.
Tribal groups today have terrible land and strange circumstances. It’s my impression that tribal groups found by European explorers very frequently had strong altruism internally.
From what I understand, speciation takes much, much longer than normal mutation. Wouldn’t that mean that species selection happens much slower, and by extension with much less effect. Do flowers speciate really fast? Does the more significant difference between the species allow it to evolve faster enough to make up for it?
Interestingly, yes, they often do. It’s a thing called polyploidy, which happens very frequently in plants.
Edit: I’m thinking this must be (a big part of) why self-compatible nightshades speciate faster—very difficult to start a new tetraploid species if you can’t self-pollinate.
I also upvoted you for making an accurate prediction:)
The rates of speciation are hardly stable—it’s a reason why there’s so much controversy over the history of Deschampsia antarctica, a grass species growing in Maritime Antarctica, Subantarctic and in Chile, I think. People argue whether it was recently introduced to Antarctica (which is unlikely, given the gap between it and S America) or has survived there since before it grew the ice shield (which is unlikely, given how similar are plants from remote locations.)
If speciation rates were easily determined, this would not be much of a question.
I think that everyone sensible agrees that group selection happens within an ontology with the categories ‘individual selection’ and ‘group selection’. The question is whether it’s ever useful from the perspective of an ontology with the category ‘gene’s eye view selection’ and whether, in the earlier ontology, it’s a good idea to set priors strongly against group selection being needed to explain any individual phenomenon.
From the 1960s through Dawkins’ Selfish Gene—and even today, in John Alcock’s Animal Behavior—you can find many examples of prominent biologists stating that group selection, including species selection, is either flat-out impossible, or so improbable that it should never be considered; and that people who suggest it is possible are fools. (It should set off big red flashing warning lights in peoples’ minds when they see the author of a scientific work criticizing not just a view, but the people who hold it.)
There is more acceptance of it today among scientists; but many lay-people, including many well-informed lay-people on this newsgroup, still think that the religious zealotry of Richard Dawkins against group selection in The Selfish Gene represents the state of the field today. I infer that Eliezer, who is somewhat influential on this site, holds that view, since his post claiming that group selection is impossible has a green dot of approval, while mine showing that it happens in nature does not.
I don’t understand. If group selection occurs; and if it is never useful from some perspective; then that is a wrong perspective.
Some category can be useful within some methodology but not within some other methodology.
Well, regarding the gene’s eye view, the example I just cited above (Henrich 2010) about group selection in culture is not relevant; while the main example in this post (selection against SC species in flowering plants) is purely genetic. So group selection is relevant to the gene’s eye view.
Picking out the circumstances in which it would be a likely suspect to explain an observation would be the next step.
But I get the impression that a lot of readers here are still stuck way back at the “group selection can’t possibly exist!” step.
This should be “rI > rC + qIC”, otherwise SI would have gone extinct instead of there being a positive equilibrium level.
Good catch! Fixed.
I’m not sure from your essay what you mean by group selection at all.
Group selection, as I’ve heard it explained before, is the idea that genes spread because their effects are for the good of the group, or species. The whole point of evolution is that genes do well because of what they do for the survival of the gene. The effect isn’t on the group, or on the individual, the species, or any other unit other than the unit that gets copied and inherited.
The question that seems obvious is how self-incompatibility ever evolved in the first place, It must have arisen in a species that was self-compatible, and then gradually have risen to fixation in that species. The opposite can happen.
Let’s look at this from the point of view of a gene. Suppose a particular mutation in a single gene results in self-compatibility. What’s the story for the gene? Let’s suppose that it gives an overwhelming advantage over outside genes in fertilising itself, plus a normal chance at fertilising others. That gene ought to do well.
Well, maybe. If the plant has a typical set of recessive genes in its genome, self-fertilisation is a disaster. A few generations down the line, the self-fertilising plant will have plenty of genetic problems arising from recessive gene problems, and will probably die out. This means that self-fertilisation is bad—a gene for self-fertilisation will only prosper in those cases where it’s not fertilising itself.
So let’s change the scenario and assume the self-fertiliser manages to create a clone instead. Now many plants actually do cloning—it’s not inherently a bad idea. But even a good clone is not as good as a gene pool. Your neighbouring plants further up the hill might have specific adaptations to the soil up there that yours doesn’t have. The self-cloning plant can’t live there. Further south, where the climate is different—your clone won’t grow there. It will not spread throughout a whole range of environments as well as a species with an established gene pool can.
The general theme of clones is that they do very well for a while. But they can’t spread outside their original environment because they can’t reshuffle genes from the general gene pool. Then some disease springs up. Either it kills none of the clones, or essentially all of them. The regular gene pool suffers some losses, but has some survivors too.
Flowering is optional, but survival is compulsory. When times are hard, you put off sexual reproduction until later, and do just as well as any clone ever could. In really tough times, the variations in the sexual plants may prove to be the difference (for some of them) between survival and death, whilst all the clones end up perishing.
So many plants do a bit of both. They clone themselves when the going is good. Then they reproduce sexually after a while, when the benefits of rearrangement outweigh the costs of all the pollen, flowers etc. There are benefits, otherwise they wouldn’t bother.
Group selection is group selection: selection of groups. That means the phenotype is group behavior, and the effect of selection is spread equally among members of the group. If the effect is death, this eliminates an entire group at once—and the nearer a selfish gene approaches fixation, the more likely it is to trigger a group extinction. Consider what would happen if you ran Axelrod’s experiments with group selection implemented, so that groups went extinct if total payoff in the group below some threshold.
The key point is nonlinearity. If the group fitness function is a nonlinear function of the prevalence of a gene, then it dramatically changes fixation and extinction rates.
No. Self-fertilisation doesn’t prevent cross-fertilisation. The self-fertilizer has just as many offspring from cross-fertilization as the self-sterile plant, but it has in addition clones of itself. Many of these clones may die, but if just one of them survives, it’s still a gain.
Reply
It might make more sense to think of one technology or one form of social organization pushing others out of existence. Human beings (and the rest of the environment) could be thought of as the resources used for propagation.
In this context group selection seems like an obviously important idea for understanding certain salient phenomena.
I think most people find it easier to believe in group selection for altruism in the evolution of culture than in the evolution of organisms. For one thing, people think about culture and can change the rules, so that complex adaptations, like punishing free-riders, can appear quickly.
ETA: the evolution of multicellularity seems like a good candidate for group selection to me. Once it has been achieved, few would call it altruism or a group, but the intermediate stages probably require group selection.
I’m putting this on the comment about culture because multicellularity involves commitment mechanisms, which are like ways of punishing free-riders.
One level’s organism is another level’s gene? Not exactly, but there may be some use for that idea.
That argument is invalid. Adaptations arise as a result of differential reproductive success. Some haystacks do indeed do better than others in contributing to future haystacks—since they contain more individuals which contribute to the big pool of individuals, from which the next generation of haystacks is produced. So: Maynard Smith’s model is just fine in this respect.
The Harpending and Rogers model from 1987 that you critique works in the same way.
Selection does not require different rates of extinction if there are different levels of reproductive sucecss.
You’re assuming that the benefits of an adaptation can only be linear in the fraction of group members with that adaptation. If the benefits are nonlinear, then they can’t be modeled by individual selection, or by kin selection, or by the Haystack model, or by the Harpending & Rogers model, in all of which the total group benefit is a linear sum of the individual benefits.
For instance, the benefits of the Greek phalanx are tremendous if 100% of Greek soldiers will hold the line, but negligible if only 99% of them do. We can guess—though I don’t know if it’s been verified—that slime mold aggregative reproduction can be maintained against invasion only because a slime mold aggregation in which 100% of the single-cell organisms play “fairly” in deciding which of them get to produce germ cells survives, while a slime mold aggregation in which just one cell’s genome insisted on becoming the germ cell would die off in 2 generations. I think individual selection would predict the population would be taken over by that anti-social behavior.
The red queen hypothesis for sex (which is pretty close to the paper you cite) has always seemed to me to be a group selection claim. Yet it is popular with people who seem to reflexively condemn group selection. Perhaps they are more sophisticated than their rhetoric.
ETA:
Huh. maybe this isn’t the red queen.
How group selection? As I understand it, Red Queen advises an organism that its descendants will be more successful if they are diverse, rather that being a bunch of identical copies. That argument may involve extrapolating more than a single generation into the future—something evolutionary theorists are usually reluctant to do—but it does not seem to involve group selection. As long as your own descendants are diverse, you don’t care that everyone else’s descendants constitute a monoculture—they are the ones that die in the ensuing epidemic, not your folk.
I cringe a bit when I read evolutionary things presented this way. It makes a kind of sense from the perspective of a personified advisor but even so caries a huge risk of confusing people. It’s backwards, dammit, improved reproductive success because of traits that produced desirable outcomes multiple generations in the past.
(I do not think you are confused and I upvoted your comment.)
I sympathize. I have a related cringe whenever anyone mentions Omega and Timeless or acausal decision theories. At least I hope my cringe is related because I don’t want to think that the people who mention these things are actually confused.
That’s generous of you. I know you are particularly wary of TDT, etc. :)
Yes, some arguments against altruism do not apply as well to sex because there is less danger of being invaded by free-riders. But what they have in common is a short-term cost cost to the individual balanced against a long-term danger of the whole group losing. Group selection is an amorphous word and I don’t think it’s terribly important if we label any particular example with it, but I think there is a great danger of using it to mean “arguments I disagree with.”
I hope I am not doing that thing you call dangerous. But it is not quite true that careless labeling is harmless to a rationalist. Recall that this entire discussion took off when Phil cited a paper dealing with sex (selfing). He called it a paper about group selection whereas I preferred to call it a paper about species selection. What difference does it make how you label it? Well, please recall the reason Phil cited the paper. He called it the best evidence yet that group selection works. And he did so in response to EY’s anti-group-selection interjection where the focal example had nothing at all to do with sex or speciation.
So is the paper Phil cited evidence against EY? I suppose it depends upon whether Phil’s paper is about group selection or not.
The focal example was foxes (a species) adapting to control their eating of rabbits to avoid exterminating them. That’s species selection.
His key objection is mathematical: “Specifically, the requirement is [C < FB] where C is the cost of altruism to the donor, B is the benefit of altruism to the recipient, and F is the spatial structure of the population: the average relatedness between a randomly selected organism and its randomly selected neighbor.” This applies equally to clades, species, and smaller groups. So if it’s a knockdown argument against small-group selection, it’s also a knockdown argument against species selection, which exists.
And, as I pointed out in my post, the problem with that analysis is that it assumes that there is no selection of groups. It’s arguing against a strawman “group selection” theory that has no selection. The argument thus both fails analytically, and is disproven by an example that it applies to.
You must be thinking of a different EY interjection than I was when I wrote that. I meant this EY comment:
which responded to this comment of yours:
No foxes, no sex, and no species selection in what I was talking about. Edit: Inflamatory and non-responsive comment deleted.
DSW holds rather extreme views on the topic of group selection. I would classify this particular comment as being nonsense.
Thus demonstrating that a sort of species selection can exist, because species can’t breed with each other and therefore can’t be infected by SC genes from other species, while group selection can’t exist, SC always infects.
That’s technically true, but it doesn’t help a lot. You’re assuming one starts with fixation to non-SC in a species. But how does one get to that point of fixation, starting from fixation of SC, which is more advantageous to the individual? That’s the problem.
In orchids (at least), not only between-species, but between-genus breeding has place. And species like Epipactis helleborine have flexible approach to SC/SI.
The 1960′s seem to have been a good time for theories about social processes, cooperation, and competition and they collected a lot of data based on the theories. I suspect that many of the broad conclusions from this era were frequently wrong, but the books they wrote have a lot of fascinating observations organized by these sorts of themes.
Your post-script reminded me of “noyau” from the book The Territorial Imperative (1966). A noyau in a canonical form is a geographic clumping of organisms of the same species who squabble and fight incessantly (which seems to indicate that they don’t like each other’s presence) but who do not actually seem to be constrained by environmental resource limitations from dispersing across the landscape. There is plenty of empty space, but they ignore it almost as if they are built so that they enjoy forming themselves into small groups and then dramatically squabbling with other small groups within the larger noyau.
I can imagine a lot of theories that might be made up to account for such observations, and I’m not sure of any of them are true so I won’t bother with specific theorizing, but I just thought it would be interesting to other readers to read about these situations. Chapter five is the one specifically about noyau.
I tried Google. First, I got:
noyau: A French liqueur made in the past from brandy and bitter almonds or apricot kernels, sometimes coloured pink.
{noyau, animals} got me:
Noyau: Animals have overlapping home ranges, and the sexes don’t live together. There’s no territoriality. Each female has a home range while males have larger home ranges that cover several female ranges. This is the system seen in orangutans. Usually goes with a promiscuous mating system.
Is the squabbling actually mate competition?
The thing Robert Ardrey, the author, was trying to describe under the term “noyau” in his book (which is online in its entirety) was probably distinct from mate competition because the author had already covered leks in a previous chapter and was trying to talk about seemingly distinct behavior that was also related to “space management by animals”.
If you look at the chapter on noyau that I linked to you’ll find (among other things) a popular recounting of the behavior of Callicebus moloch ornatus, studied by William A. Mason. The report is that these monkeys have very precisely defined territories where entire family groups (mother, father, and kids) line up in the mornings to shriek and scuffle with neighboring family groups. The species is not especially sexually dimorphic and males and females pair bond for life… but when the females are in heat once a year all the territories dissolve and there is basically an orgy. Afterwards, the families reform as before and go back to squabbling with each other every morning.
My guess is that this book has packaged up a lot of interesting stories from animal ethology and used terms and theory that may have been partially novel with the novelty partially catching on in larger scientific circles (and so the contents of the book may be interwoven with falsehood and/or be difficult to google by this point). It was the stories themselves about actual animals, in the specific links that I was trying to gesture towards as “potentially interesting”.
You must mean ‘still SI’.
Yep! Thanks. Fixed.
Regarding the terminology, if group selection translates to selection of a set of individuals, then how is group selection really valuably distinct from individual selection?
And, regarding the terminology, around “If group-level selection occurs at all, then traits of the group that are not genetic traits, including cultural knowledge, must be considered.” you seem to miss accounting for the possibility of individual selection for cultural units. And regarding those, analogously the first question again: is group selection of group of cultural units really meaningfully distinct from individual selection on a set of cultural units, as happens since time immemorial due to e.g. a weather event?
My suspicion is it isn’t, and—as you allude to—the false distinction is used to shoehorn wishes for altruism into evolutionary theory.
I would also go so far as to argue that the very concept of “group”, which supports this theory as well as the practice it refers to, is itself an individual cultural unit.
Thanks for raising this issue! I think resolving it could yield great benefits, and I’ll contribute to it when I can post on this forum.
What about group_selection_p, where group selection makes a gene that is already beneficial on the individual level spread even faster?
group_selection_p
I meant something like gs_d = gs_n + gs_p. (The various gs_x I used are not standard terminology, BTW. Also BTW, you can get your _ to show up by putting \ before them.)
Another interesting platform for kin vs. group selection is family Pyrolaceae (see Hideki Takahashi (1986) Pollen polyads and their variation in chimaphila (pyrolaceae), Grana, 25:3, 161-169) .
Without going into too much detail, it has about 4 genera; of them, Chimaphila has pollen organized into groups of about a hundred grains! It means that when the polyad (that’s what the clump is called) lands on a stigma, multiple ovules (females) will get sperm (males) from the same father, and the resulting offspring should be much closer genetically than if multiple fathers contributed in equal measures. (My intuition is that fertilization is not frequent in these plants, though I have seen the fruits.) That is definite evidence for kin selection, isn’t it? However, why is it not more widespread? “Three other generain the Pyrolaceae, Orthilia , Pyrola, and Moneses, have flowers with numerous ovules like that of Chimaphila, but the first of these produces pollen monads and the two others pollen tetrads.” Also, [I think that] at least in Ukraine Orthilia and Pyrola are more common than Chimaphila (which is, even if actually true, only anecdotal evidence considering the total ranges of the genera.) (Another problem is that all those plants need fungal symbionts, and there’s little data on their diversity.) What differencies in seed quality & dispersion, and population strategies would kin selection predict for Chimaphila and (Pyrola and Orthilia)?
Sorry; your example is interesting and potentially useful, but I don’t follow your reasoning. This manner of fertilization would be evidence that kin selection should be strong in Chimaphila, but I don’t see how this manner of fertilization is itself evidence that kin selection has taken place. Also, I have no good intuitions about what differences kin selection predicts in the variables you mentioned, except that maybe dispersion would be greater in Chimaphila because of teh greater danger of inbreeding. Also, kin selection isn’t controversial, so I don’t know where you want to go with this comment.
Not from Solanaceae, but tangentially related. (It is studies like this one that set people like me to wonder at the selfing/crossing problem:)) possibly even a low-hanging fruit here:))
C. Montaner , E. Floris & J. M. Alvarez (2003): Study of pollen cytology and evaluation of pollen viability using in vivo and in vitro test, in borage (Borago officinalis L.) , Grana, 42:1, 33-37:
...It was stated that [borage’s] pollen is difficult to germinate in vitro, it loses viability shortly after anther dehiscence and in the case of incompatible pollinations pollen tubes tend to be inhibited on the stigmatic surface (Mulcahy & Mulcahy 1983). Ghorbel and Nabli (1998) said that borage pollen remained dehydrated after self-pollination, like a sign of self-rejection. However, Crowe (1971) affirmed that the incompatibility reaction occurs after fertilization although our data (Montaner et al. 2000 a) demonstrated that there is not self-incompatibility and incompatible crosses have not been detected...
I mean, what the..? Is it, or is it not, self-incompatible?.. Although I must say that I haven’t looked on articles citing this one.
Is this supposed to mean: different groups exist, whose members’ success or failure is tied together, so that we can sometimes expect to see group members with adaptations that would be self-destructive in the absence of its group?
That sounds like what I called group_selection_c. You might also be interested in selection at the group level even if it is based on adaptations that would be neutral in the absence of the group; or adaptations that can be said to be a feature of the group more than a feature of individuals (e.g., social conventions).
Got it.
I guess I found “at the level of a group” to be vague. It turns out that its the groups that are supposed to be selected. This could be made more clear in the initial definition of “group selection”, although it was completely obvious by the time I finished reading the whole post.
I’m not sure from your essay what you mean by group selection at all.
Group selection, as I’ve heard it explained before, is the idea that genes spread because their effects are for the good of the group, or species. The whole point of evolution is that genes do well because of what they do for the survival of the gene. The effect isn’t on the group, or on the individual, the species, or any other unit other than the unit that gets copied and inherited.
The question that seems obvious is how self-incompatibility ever evolved in the first place, It must have arisen in a species that was self-compatible, and then gradually have risen to fixation in that species. The opposite can happen.
Let’s look at this from the point of view of a gene. Suppose a particular mutation in a single gene results in self-compatibility. What’s the story for the gene? Let’s suppose that it gives an overwhelming advantage over outside genes in fertilising itself, plus a normal chance at fertilising others. That gene ought to do well.
Well, maybe. If the plant has a typical set of recessive genes in its genome, self-fertilisation is a disaster. A few generations down the line, the self-fertilising plant will have plenty of genetic problems arising from recessive gene problems, and will probably die out. This means that self-fertilisation is bad—a gene for self-fertilisation will only prosper in those cases where it’s not fertilising itself.
So let’s change the scenario and assume the self-fertiliser manages to create a clone instead. Now many plants actually do cloning—it’s not inherently a bad idea. But even a good clone is not as good as a gene pool. Your neighbouring plants further up the hill might have specific adaptations to the soil up there that yours doesn’t have. The self-cloning plant can’t live there. Further south, where the climate is different—your clone won’t grow there. It will not spread throughout a whole range of environments as well as a species with an established gene pool can.
The general theme of clones is that they do very well for a while. But they can’t spread outside their original environment because they can’t reshuffle genes from the general gene pool. Then some disease springs up. Either it kills none of the clones, or essentially all of them. The regular gene pool suffers some losses, but has some survivors too.
Flowering is optional, but survival is compulsory. When times are hard, you put off sexual reproduction until later, and do just as well as any clone ever could. In really tough times, the variations in the sexual plants may prove to be the difference (for some of them) between survival and death, whilst all the clones end up perishing.
So many plants do a bit of both. They clone themselves when the going is good. Then they reproduce sexually after a while, when the benefits of rearrangement outweigh the costs of all the pollen, flowers etc. There are benefits, otherwise they wouldn’t bother.
I’m not sure from your essay what you mean by group selection at all.
Group selection, as I’ve heard it explained before, is the idea that genes spread because their effects are for the good of the group, or species. The whole point of evolution is that genes do well because of what they do for the survival of the gene. The effect isn’t on the group, or on the individual, the species, or any other unit other than the unit that gets copied and inherited.
The question that seems obvious is how self-incompatibility ever evolved in the first place, It must have arisen in a species that was self-compatible, and then gradually have risen to fixation in that species. The opposite can happen.
Let’s look at this from the point of view of a gene. Suppose a particular mutation in a single gene results in self-compatibility. What’s the story for the gene? Let’s suppose that it gives an overwhelming advantage over outside genes in fertilising itself, plus a normal chance at fertilising others. That gene ought to do well.
Well, maybe. If the plant has a typical set of recessive genes in its genome, self-fertilisation is a disaster. A few generations down the line, the self-fertilising plant will have plenty of genetic problems arising from recessive gene problems, and will probably die out. This means that self-fertilisation is bad—a gene for self-fertilisation will only prosper in those cases where it’s not fertilising itself. It will do worse.
So let’s change the scenario and assume the self-fertiliser manages to create a clone instead. Now many plants actually do cloning—it’s not inherently a bad idea. But even a good clone is not as good as a gene pool. Your neighbouring plants further up the hill might have specific adaptations to the soil up there that yours doesn’t have. The self-cloning plant can’t live there. Further south, where the climate is different—your clone won’t grow there. It will not spread throughout a whole range of environments as well as a species with an established gene pool can.
The general theme of clones is that they do very well for a while. But they can’t spread outside their original environment because they can’t reshuffle genes from the general gene pool. Then some disease springs up. Either it kills none of the clones, or essentially all of them. The regular gene pool suffers some losses, but has some survivors too.
Flowering is optional, but survival is compulsory. When times are hard, you put off sexual reproduction until later, and do just as well as any clone ever could. In really tough times, the variations in the sexual plants may prove to be the difference (for some of them) between survival and death, whilst all the clones end up perishing.
So many plants do a bit of both. They clone themselves when the going is good. Then they reproduce sexually after a while, when the benefits of rearrangement outweigh the costs of all the pollen, flowers etc. There are benefits, otherwise they wouldn’t bother.
I’m not sure from your essay what you mean by group selection at all.
Group selection, as I’ve heard it explained before, is the idea that genes spread because their effects are for the good of the species. The whole point of evolution is that genes do well because of what they do for the survival of the gene. The effect isn’t on the group, or on the individual, the species, or any other unit other than the unit that gets copied and inherited.
The question that seems obvious is how self-incompatibility ever evolved in the first place, It must have arisen in a species that was self-compatible, and then gradually have risen to fixation in that species. The opposite can happen.
Let’s look at this from the point of view of a gene. Suppose a particular mutation in a single gene results in self-compatibility. What’s the story for the gene? Let’s suppose that it gives an overwhelming advantage over outside genes in fertilising itself, plus a normal chance at fertilising others. That gene ought to do well.
Well, maybe. If the plant has a typical set of recessive genes in its genome, self-fertilisation is a disaster. A few generations down the line, the self-fertilising plant will have plenty of genetic problems arising from recessive gene problems, and will probably die out. This means that self-fertilisation is bad—a gene for self-fertilisation will only prosper in those cases where it’s not fertilising itself. It will do worse.
So let’s change the scenario and assume the self-fertiliser manages to create a clone instead. Now many plants actually do cloning—it’s not inherently a bad idea. But even a good clone is not as good as a gene pool. Your neighbouring plants further up the hill might have specific adaptations to the soil up there that yours doesn’t have. The self-cloning plant can’t live there. Further south, where the climate is different—your clone won’t grow there. It will not spread throughout a whole range of environments as well as a species with an established gene pool can.
The general theme of clones is that they do very well for a while. But they can’t spread outside their original environment because they can’t reshuffle genes from the general gene pool. Then some disease springs up. Either it kills none of the clones, or essentially all of them. The regular gene pool suffers some losses, but has some survivors too.
Flowering is optional, but survival is compulsory. When times are hard, you put off sexual reproduction until later, and do just as well as any clone ever could. In really tough times, the variations in the sexual plants may prove to be the difference (for some of them) between survival and death, whilst all the clones end up perishing.
So many plants do a bit of both. They clone themselves when the going is good. Then they reproduce sexually after a while, when the benefits of rearrangement outweigh the costs of all the pollen, flowers etc. There are benefits, otherwise they wouldn’t bother.
Group selection is group selection: selection of groups. That means the phenotype is group behavior, and the effect of selection is spread equally among members of the group. If the effect is death, this eliminates an entire group at once—and the nearer a selfish gene approaches fixation, the more likely it is to trigger a group extinction. Consider what would happen if you ran Axelrod’s experiments with group selection implemented, so that groups went extinct if total payoff in the group below some threshold.
The key point is nonlinearity. If the group fitness function is a nonlinear function of the prevalence of a gene, then it dramatically changes fixation and extinction rates.
No. Self-fertilisation doesn’t prevent cross-fertilisation. The self-fertilizer has just as many offspring from cross-fertilization as the self-sterile plant, but it has in addition clones of itself. Many of these clones may die, but if just one of them survives, it’s still a gain.
It’s not that I no longer endorse it; it’s that I replied to a deleted comment instead of to the identical not-deleted comment.
Another recent article on group selection:
Henrich et al (2010). Markets, religion, community size, and the evolution of fairness and punishment. Science 327, March 19 2010, p. 1480.
Their theory: “Larger and more-complex societies prospered and spread to the degree that their norms and institutions effectively sustained successful interaction in ever-widening socioeconomic spheres, well beyond individuals’ local networks of kin and long-term relationships.”
Their evidence: “Using 3 behavioral experiments administered across 15 diverse populations, we show that market integration (measured as percentage of purchased calories) positively covaries with fairness while community size positively covaries with punishment.”