Professor Pinker’s critique of group selection rests broadly on three points. First, he suggests that the concept is inexplicit as “it refers to too many things.” Second, if group selection is used to explain cultural traits, it contributes nothing new, i.e. nothing that cannot be explained by anthropologists, historians, social scientists, and the like without recourse to group selection. Further, according to Pinker group selectionists make no explicit use of selection as a mechanism of explanation [and prediction]. Third, altruistic behavior does not need to be explained by group selection as there is an automatic benefit to sacrificing for kin and, more importantly, there appears to be no evidence for group selected traits. I will not address all of these but focus on what I believe to be the biological reality of group selection and then discuss the significance of group selection with respect to the study of human history and historical processes.
In response, first so that there is no confusion on the matter, let me say that I fall squarely within the camp supporting group selection. This response will now consider genome organization at the level of the chromosome and then the phenomenon of mutualisms at the population level of organization as foci for group selection. Pinker treats genes as if they were discrete units much as Dalton’s model of the atom, however, it is their function that is subject to selection as well as their position within the genome and their structure. Consequently, what does the structure of the genome in relation to its function suggest about the reality of group selection? With regard to organisms themselves, the environment in its broadest sense imposes selection pressures on individuals, however, it is the gene pool as it is housed within populations of individuals that persists over time. Individuals also alter or construct the environment during their tenure in it, which in turn imposes altered (and new) selection pressures on the endemics. Is there evidence for the effects of group selection with respect to the group and its reciprocal interactions with its environment? Ultimately, does group selection play any role in the processes of human history?
Genome organization betrays the effects of group selection. It appears that all genomes are compartmentalized into chromosomes. There are no bean bag genomes where every bean is a single gene; genes are organized in physically connected groups, i.e. chromosomes. Also, genes interact, and their collective interaction is the focus of selection. Further, within eukaryotic chromosomes there are inversions which tie genes together and prohibit the effects of crossing over dismantling the inverted gene set. In other words, while the linked genes on chromosomes can be disrupted by crossing over, this recombinatorial process does not disrupt and recombine the entire set of genes on the chromosome, and within chromosomes there are genes that are even more tightly tied together, genes whose collective function is selected for, is adaptive, and whose integrity is maintained until the entire set of genes is selectively disfavored. In other words, the inverted sequence, the group of genes, is inherited as a unit, is reproduced as a unit, is subject to selection as a unit, and is of course maintained as a unit. This is only a single example, however, and without being encyclopedic, there is clear evidence of sets of genes and therefore their collective function, being the object of selection, i.e. the set or group is the focus of selection and not individual genes.
This response will now focus on the population level of biological organization for the very good reason that it is the population that can persist through time, not the individual, and as a result it is the population that can produce on-going changes in the environment which can further feedback on the population in the form of new selection pressures. Ultimately if the interaction between organisms and environments can persist, can be maintained over time, the interaction itself can become the object of selection. Mutualisms, and domestication for instance falls within this category, are examples of these sustained interactions between organism and environment, some of which become so tight, so constrained, that they become organismic in scale. As an example, nitrogen fixing bacteria that become add-ons to the roots of certain plants are examples of this tightness of fit. The implication here is clear, that the interaction between a population of organisms and their symbionts brings about a new biological synthesis which represents a population of new biological entities, ones which now becomes subject to selection.
Where does this leave us with respect to insight into the processes of human history? Here Pinker is pointedly critical, as he suggests that group selection has nothing new to offer, and in fact the real experts, the anthropologists, historians of course, and other social scientists et al, will continue to be the only ones with their hands on the pulse of historical research. This is doubtful. First, all of historical analysis has not been done; there will be new concepts and new discoveries into the foreseeable future. So, as long as we have a future, we also have a new past to consider. As a result a group selectionist perspective may well reveal new ideas and new concepts. Paradigmatic change in human understanding can very often be brought about by either neophytes or complete outsiders, and no discipline of human endeavor appears to be free of these shifts; this is certainly true of history. So, approaching the study of history and historical processes from the group selectionist perspective is reasonable and may be quite revelatory.
Let’s consider one historical mutualism of humans, the domestication of the dog. Steiner and Feeley-Harnik (2012) state, “Domestication……took place at the interface between humans and animals and was the by-product of selection processes that formed naturally in that space. Humans are evolutionary partners in domestication relationships.” The relationship of domestication that evolved between humans and canines is an entity that is itself subject to selection. If some groups of paleo-humans were able to domesticate wolves while others were not, it is entirely possible that those groups that were had a selective advantage and would have survived at the expense of those that did not. Beyond the survival of groups, was there any selection for various human traits including psychologies within the groups exploiting domestication that enabled the domestication process, traits that had to be to some extent genetically underpinned? If the answer is, yes, then selection for the mutualism underpinned by the genetics of both human and canine occurred at the level of interaction of two groups of organisms. Mutualisms then may well be an example of adaptations resulting from group selection.
Two broad classes of examples of group selection have been offered in response to Pinker’s critique. The genetic material itself is organized so that it is a genetic collective, and some portions of that collective are significantly more dependent on the stable structure of the genetic environment than others. Inverted regions of eukaryotic chromosomes function as units and largely persist or extinguish with respect to selection of the whole set or group of genes. Mutualisms as part of the human history, specifically domestications, have also been shown to be subject to group selection, and it has been suggested that mutualisms can be examples of group adaptations. Where historians and social scientists in general can help this process is to identify examples of relationships that fall under the group adaptation category and further show that the identified adaptation has enhanced the survival and persistence over time in comparison to a competing group.
I have two further comments. While good science thrives and in fact requires competing models, the resolution of scientific competition in turn requires supporting evidence. To date the evidence for group selection is strongly suggestive and growing but not conclusive, at least as conclusive as one would like. [Certainly Pinker doesn’t like it.] So, clearly and especially within the domain of human history and historical processes more evidence is required. However, that is what the future is about. There is also another aspect to this controversy that requires attention. Those in favor of group selection and those against appear at times to be talking at cross purposes, a characteristic if one will recall of paradigm shifts (Kuhn, 1970), with respect to what is selected and what is reproduced. E. O. Wilson (2011) says it most effectively when he suggests that there is a distinction between the units of heredity and the focus of selection, and, in fact, this notion may be at the core of the debate between the primacy of individual selection and the reality of group selection. Are those engaged in this debate addressing the same issues or are the different paradigms incommensurable?
References
Kuhn, Thomas. 1970. The Structure of Scientific Revolutions. U. of Chicago Press.Chicago.
Odling-Smee, F. John, Kevin N. Laland, and Marcus W. Feldman. 2003. Niche Construction: The Neglected Process in Evolution. Princton U. Press.Princeton.
Steiner, Mary C. and Gillian Feeley-Harnik. 2011. Energy and Ecosystems. In Deep History: The Architecture of Past and Present. By Andrew Shryock and Daniel Lord Smail.University of California Press. Berkeley.
Wilson, Edward O. 2011. The Social Conquest of Earth. W. W. Norton. New York.
One might add to this excellent comment that many insects have managed to create agriculture and domestication without even having big brains. Several leafcutter ant and bark and ambrosia beetles cultivate fungi, and have selected special strains.
Indeed, an excellent comment. The chromosome example is very good, because different genes sitting on the same chromosome are not ‘kin’ to each other in any reasonable terminology.
I don’t know if anybody considered evolution of mutualisms from the MLS point of view, but it makes a lot of sense to me, and should be done.
Finally, note that both Tony and David in previous commentary talk about paradigm shifts a la Kuhn. I think they are right, we are in a middle of such shift roght now.
Meiosis and cross-over do not separate gene complexes in addition because most genes in an organism are fixed, so individuals are homozygous and the same alleles are broadly shared by the gametes that form zygotes.
Herb, still the action is where there is variability. If we think of different gene complexes competing with each other, cross-over will sometimes disrupt such complexes, resulting in a functional equivalent of migration between groups. But we know from models that a certain amount of migration between groups is not particularly detrimental to group selection.
Additionally, there may be selection that would move genes closer to each other on the chromosome, so that the probability of cross-over is minimized. And aren’t there ways to protect pieces from cross-over?
More generally, have people done formal modeling of these processes with MLS-type models? You’d probably know this literature.
Re: “If the answer is, yes, then selection for the mutualism underpinned by the genetics of both human and canine occurred at the level of interaction of two groups of organisms. Mutualisms then may well be an example of adaptations resulting from group selection.”
Can you phrase this idea in terms of kin selection? If not, it belongs on the “bad group selection” pile – not the “good group selection” pile.
There are a number of empirical studies and theoretical models on selection of multi-species assemblages, some by myself. One of my favorites is by Charles Goodnight on 2-species flour beetle communities. Vials of flour contained two species, but the vials were selected based on the density of one of the species (the “phenotypic trait” of the community). There was a response to selection and it was due to genetic changes in both species, which interacted with each other to cause the phenotypic trait (density of one of the species).
To relate this example to Antony’s essay, imagine performing a standard artificial selection experiment at the individual level, such as selecting bristle number in Drosophila. Let’s say that there is a response to selection cause by genetic changes on different chromosomes, which interact with each other to produce the phenotypic effect. We would find this result unsurprising. Who cares if the genetic changes occurred on different chromosomes? It is the effect on the phenotype that counts. That’s what happened in Goodnight’s experiments, where selection was at the community level and the genetic changes were in different species. In essence, selecting at the community level turned the species into analogs of chromosomes.
This is a good example of an idea that makes sense in terms of MLST and involves the actual selection of higher-level units. Even if it can be explained from a IFT perspective (IFT colleagues take note!), it would be only in retrospect, since the possibility of multispecies communities as adaptive units is less forthcoming from an IFT perspective.
Tim’s comment makes no sense to me. Since when did “can be phrased in terms of kin selection” become the criterion of “good group selection”?