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Group selection is a proposed mechanism of evolution in which natural selection acts at the level of the group, instead of at the more conventional level of the individual.

Early authors such as V. C. Wynne-Edwards and Konrad Lorenz argued that the behavior of animals could affect their survival and reproduction as groups, speaking for instance of selection that was for the good of a species. No mechanism was proposed for selection of species as a whole.

From the mid 1960s, evolutionary biologists such as John Maynard Smith argued that natural selection acted primarily at the level of the individual. They argued on the basis of mathematical models that individuals would not altruistically sacrifice fitness for the sake of a group. They persuaded the majority of biologists that group selection did not occur, other than in special situations such as the haplodiploid social insects like honeybees (in the Hymenoptera), where kin selection was possible.

In 1994 David Sloan Wilson and Elliott Sober argued for multi-level selection, including group selection, on the grounds that groups, like individuals, could compete. In 2010 three authors including E. O. Wilson, known for his work on social insects especially ants, again revisited the arguments for group selection. They argued that group selection can occur when competition between two or more groups, some containing altruistic individuals who act cooperatively together, is more important for survival than competition between individuals within each group. Their proposals provoked a strong rebuttal from a large group of evolutionary biologists.

As of yet, there is no clear consensus among biologists regarding the importance of group selection. Steven Pinker expressed his ambivalence with the theory: "Human beings live in groups, are affected by the fortunes of their groups, and sometimes make sacrifices that benefit their groups. Does this mean that the human brain has been shaped by natural selection to promote the welfare of the group in competition with other groups, even when it damages the welfare of the person and his or her kin?...  I think that this reasonableness is an illusion. The more carefully you think about group selection, the less sense it makes, and the more poorly it fits the facts of human psychology and history."

However, there is active debate among specialists in many fields of study. It is possible that a theory of group selection can be modified to provide valuable explanations. Group selection could be useful for understanding the evolution of human culture, since humans form groups that are unlike any other animal. Group selection may be used to understand human history. Some researchers have used the framework to understand the development of human morality.

Early Developments
Charles Darwin developed the theory of evolution in his book, Origin of Species. Darwin also made the first suggestion of group selection in The Descent of Man that the evolution of groups could affect the survival of individual. He wrote, "If one man in a tribe... invented a new snare or weapon, the tribe would increase in number, spread, and supplant other tribes. In a tribe thus rendered more numerous there would always be a rather better chance of the birth of other superior and inventive members."

Once Darwinism had been accepted as the basis of biological evolution, some scientists used the theory in a careless way to indicate that groups or species were the basis of the mechanism of evolution. Animal behavior was glibly explained with unsubstantiated hypotheses about survival value, which was poorly specified. The naturalist Konrad Lorenz had argued loosely in books like On Aggression (1966) that animal behavior patterns were "for the good of the species", without actually studying survival value in the field; the ethologist Niko Tinbergen praised Lorenz for his interest in the survival value of behavior, and naturalists enjoyed Lorenz's writings for the same reason. In 1962, group selection was used as a popular explanation for adaptation by the zoologist V. C. Wynne-Edwards.



From the mid 1960s, evolutionary biologists argued that natural selection acted primarily at the level of the individual. In 1964, John Maynard Smith, C.M. Perrins (1964), and George C. Williams in his 1966 book Adaptation and Natural Selection cast serious doubt on group selection as a major mechanism of evolution; Williams's 1971 book Group Selection assembled writings from many authors on the same theme. In 1976, Richard Dawkins wrote a well-known book on the importance of evolution at the level of the gene or the individual, The Selfish Gene.

It was generally agreed that the primary exception of social group selection was in the social insects, and the explanation was limited to the unique inheritance system (involving haplodiploidy) of the eusocial Hymenoptera such as honeybees, which encourages kin selection, since workers are closely related.

Kin selection and inclusive fitness theory
Early group selection models assumed that genes acted independently, for example a gene that coded for cooperation or altruism. Genetically-based reproduction of individuals implies that, in group formation, the altruistic genes would need a way to act for the benefit of members in the group to enhance the fitness of many individuals with the same gene. But it is expected from this model that individuals of the same species would compete against each other for the same resources. This would put cooperating individuals at a disadvantage, making genes for cooperation tend to be eliminated. Group selection on the level of the species is flawed because it is difficult to see how selective pressures would be applied to competing/non-cooperating individuals.

Experiments from the late 1970s suggested that selection involving groups was possible. Kin selection between related individuals is accepted as an explanation of altruistic behavior. In this model, genetically related individuals cooperate because survival advantages to one individual also benefit kin who share some fraction of the same genes, giving a mechanism for favoring genetic selection. In a strict interpretation of the kin selection theory, a statistical association of related genes (present in the interactions of close genetic relatives) is understood as a necessary (though not sufficient) condition for the evolutionary emergence of certain traits relating to social cooperation.

Inclusive fitness theory, first proposed by W. D. Hamilton in the early 1960s, gives a selection criterion for evolution of social traits when social behavior is costly to an individual organism's survival and reproduction. This behavior could emerge under conditions such that the statistical likelihood that benefits accrue to the survival and reproduction of other organisms whom also carry the social trait. Inclusive fitness theory is a general treatment of the statistical probabilities of social traits accruing to any other organisms likely to propagate a copy of the same social trait. Kin selection theory treats the narrower but simpler case of the benefits to close genetic relatives (or what biologists call 'kin') who may also carry and propagate the trait. A significant group of biologists support inclusive fitness as the explanation for social behavior in a wide range of species, as supported by experimental data. An article was published in Nature with over a hundred coauthors.

One of the questions about kin selection is the requirement that individuals must know if other individuals are related to them, or kin recognition. Any altruistic act has to preserve similar genes. One argument given by Hamilton is that many individuals operate in "viscous" conditions, so that they live in physical proximity to relatives. Under these conditions, they can act altruistically to any other individual, and it is likely that the other individual will be related. This population structure builds a continuum between individual selection, kin selection, kin group selection and group selection without a clear boundary for each level. However, early theoretical models by D.S. Wilson et al. and Taylor showed that pure population viscosity cannot lead to cooperation and altruism. This is because any benefit generated by kin cooperation is exactly cancelled out by kin competition; additional offspring from cooperation are eliminated by local competition. Mitteldorf and D.S. Wilson later showed that if the population is allowed to fluctuate, then local populations can temporarily store the benefit of local cooperation and promote the evolution of cooperation and altruism. By assuming individual differences in adaptations, Yang further showed that the benefit of local altruism can be stored in the form of offspring quality and thus promote the evolution of altruism even if the population does not fluctuate. This is because local competition among more individuals resulting from local altruism increases the average local fitness of the individuals that survive.

Another explanation for the recognition of genes for altruism is that a single trait, group reciprocal kindness, is capable of explaining the vast majority of altruism that is generally accepted as "good" by modern societies. The phenotype of altruism relies on recognition of the altruistic behavior by itself. The trait of kindness will be recognized by sufficiently intelligent and undeceived organisms in other individuals with the same trait. Moreover, the existence of such a trait predicts a tendency for kindness to unrelated organisms that are apparently kind, even if the organisms are of a completely different species. The gene need not be exactly the same, so long as the effect or phenotype is similar. Multiple versions of the gene—or even meme—would have virtually the same effect. This explanation was given by Richard Dawkins as an analogy of a man with a green beard. Green-bearded men tend to cooperate with each other simply by seeing a green beard, where the green beard trait is incidentally linked to the reciprocal kindness trait. However, such a marker would also allow other individuals to recognize these marked individuals to take advantage of them in competition.

Multilevel selection theory
Kin selection or inclusive fitness is accepted as an explanation for cooperative behavior in many species, but there are some species, including some human behavior, that are difficult to explain with only this approach. In particular, it doesn't seem to explain the cause of the (relatively) rapid rise of human civilization. David Sloan Wilson has argued that other factors must also be considered in evolution. Since the 1990s, group selection models have seen a resurgence and further refinement.

In 1994, David Sloan Wilson and Elliott Sober argued that the case against group selection had been overstated. They argued that groups can have functional organization in the same way as individuals, and consequently that groups can be "vehicles" for selection. They do not posit evolution on the level of the species. Selective pressures pit individuals or small groups within a species, e.g. groups of social insects or primates, against other groups. Individuals in the groups that cooperate tend to survive and reproduce at the expense of those that do not, or more than groups dominated by internal competition. Resurrected in this way, Wilson & Sober's new group selection is called multilevel selection theory.

In 2010 three authors including E. O. Wilson argued for multi-level selection, including group selection, to correct what they saw as deficits in the explanatory power of inclusive fitness. The response was a back-lash from 137 other evolutionary biologists who argued "that their arguments are based upon a misunderstanding of evolutionary theory and a misrepresentation of the empirical literature".



D. S. Wilson compared the layers of competition and evolution to nested sets of Russian matryoshka dolls. The lowest level is the genes, next come the cells, then the organism level and finally the groups of individuals in varying numbers and functional organization. The successful levels function cohesively to maximize fitness, or genetic reproductive success of members. The theory asserts that selection at the group level, involving competition between effective groups, can outweigh competition between individuals within the groups. As a result of the group-level competition, group-benefitting traits can spread.

Peter Turchin uses the same analogy of matryoshka dolls, but uses it to show the stepwise increase in size of social groups, from villages, tribes, regional societies, to nations, and finally to empires or civilizations. He points out that humans have the capability to consider themselves as a member of the entire range of affiliations, like the smallest doll inside the entire assembly of dolls.

Multilevel selection theory focuses on the phenotype because it looks at the traits that selection directly acts upon. For humans, social norms can be argued to reduce individual level variation and competition, thus shifting selection to the group level. The assumption is that variation between different groups is larger than variation within groups. Competition and selection can operate at all levels regardless of scale. Wilson wrote, "At all scales, there must be mechanisms that coordinate the right kinds of action and prevent disruptive forms of self-serving behavior at lower levels of social organization." E. O. Wilson summarized, "In a group, selfish individuals beat altruistic individuals. But, groups of altruistic individuals beat groups of selfish individuals."

Group selection has most often been postulated in humans and, notably, eusocial Hymenoptera that make cooperation a driving force of their adaptations over time and have a unique system of inheritance involving haplodiploidy that allows the colony to function as an individual while only the queen reproduces.

In a 2005 article, E. O. Wilson argued that kin selection could no longer be thought of as underlying the evolution of extreme sociality, for two reasons. First, he suggested, the argument that haplodiploid inheritance (as in the Hymenoptera) creates a strong selection pressure towards nonreproductive castes is mathematically flawed. Second, eusociality no longer seems to be confined to the hymenopterans; increasing numbers of highly social taxa have been found in the years since Wilson's foundational text on sociobiology was published in 1975, including a variety of insect species, as well as two rodent species (the naked mole-rat and the Damaraland mole rat). Wilson suggests the equation for Hamilton's rule:
 * rb > c

(where b represents the benefit to the recipient of altruism, c the cost to the altruist, and r their degree of relatedness) should be replaced by the more general equation
 * rbk + be > c

in which bk is the benefit to kin (b in the original equation) and be is the benefit accruing to the group as a whole. He then argues that, in the present state of the evidence in relation to social insects, it appears that be>rbk, so that altruism needs to be explained in terms of selection at the colony level rather than at the kin level.

However, kin selection and group selection are not distinct processes, and the effects of multi-level selection are already accounted for in Hamilton's rule, rb>c, provided that an expanded definition of r, not requiring Hamilton's original assumption of direct genealogical relatedness, is used, as proposed by E. O. Wilson himself.

The use of the Price equation to support group selection was challenged by van Veelen in 2012, arguing that it is based on invalid mathematical assumptions.

Gene-culture co-evolution in humans


Gene-culture coevolution (also called dual inheritance theory) is a hypothesis that combines evolutionary biology and modern sociobiology. It treats culture as an evolutionary system that acts in parallel to and in combination with genetic evolution to transform human traits. This combination of genetic influence with cultural influence can feed back with each other over several generations. It is not included in the other hypotheses such as reciprocal altruism and kin selection.

Fehr provides evidence of group selection taking place in humans presently with experimentation through logic games such as prisoner’s dilemma, the type of thinking that humans have developed many generations ago.

D. S. Wilson tied the multilevel selection theory regarding humans to gene-culture co-evolution by acknowledging that culture can characterize a group-level mechanism for human groups to adapt to environmental changes. It also involves genetic selection of individuals who operate successfully within groups. Gene-culture co-evolution allows humans to develop highly distinct adaptations to the local pressures and environments more quickly than with genetic evolution alone. Robert Boyd and Peter J. Richerson, two strong proponents of cultural evolution, postulate that the act of social learning allows human populations to accrue information over many generations. This leads to cultural evolution of behaviors and technology alongside genetic evolution. Boyd and Richerson believe that the ability to collaborate evolved during the Middle Pleistocene, a million years ago, in response to a rapidly changing climate.

In 2003, Herbert Gintis examined cultural evolution statistically, offering evidence that societies that promote pro-social norms have higher survival rates than societies that do not. Herbert Gintis wrote that genetic and cultural evolution can work together. Genes transfer information in DNA, and cultures transfer information encoded in brains, artifacts, or documents. Language, tools, lethal weapons, fire, cooking, etc., have a long-term effect on genetics. For example, cooking led to a reduction of size of the human gut, since less digestion is needed for cooked food. Language led to a change in the human larynx and an increase in brain size. Projectile weapons led to changes in human hands and shoulders, such that humans are much better at throwing objects than the closest human relative, the chimpanzee.

Differing evolutionarily stable strategies (ESSs)
The problem with group selection is that for a whole group to get a single trait, it must spread through the whole group first by regular evolution. But, as J. L. Mackie suggested, when there are many different groups, each with a different Evolutionarily Stable Strategy (ESS), there is selection between the different ESSs, since some are worse than others. For example, a group where altruism was universal would outcompete a group where every creature acted in its own interest. A mixed group of altruists and non-altruists would be vulnerable to cheating by non-altruists within the group, but might have a slight advantage over a group with less altruism if it has an appropriate ESS.

Altruism in animals
One of the problems associated with the idea of group selection is the indefinite way in which groups are defined. Without clear, definite characterization of a group, it is common to conflate benefits that may be individual fitness into an apparent group. This has been done in studies of populations of animals. In addition, animals have much less complex social behavior than humans. Spatial populations of predators and prey show restraint of reproduction at equilibrium, both individually and through social communication, as originally proposed by Wynne-Edwards. While these spatial populations do not have well-defined groups for group selection, the local spatial interactions of organisms in transient groups are sufficient to lead to a kind of multi-level selection. There is however as yet no evidence that these processes operate in the situations where Wynne-Edwards posited them. Rauch et al.'s analysis, for example, is of a host-parasite situation, which was recognised as one where group selection was possible even by E. O. Wilson (1975), in a treatise broadly hostile to the whole idea of group selection. Specifically, the parasites do not individually moderate their transmission; rather, more transmissible variants "continually arise and grow rapidly for many generations but eventually go extinct before dominating the system."

Social behaviors such as altruism and group relationships can impact many aspects of population dynamics, such as intraspecific competition and interspecific interactions. In 1871, Darwin argued that group selection occurs when the benefits of cooperation or altruism between subpopulations are greater than the individual benefits of egotism within a subpopulation. This supports the idea of multilevel selection, but kinship also plays an integral role because many subpopulations are composed of closely related individuals. An example of this can be found in lions, which are simultaneously cooperative and territorial. Within a pride, males protect the pride from outside males, and females, who are commonly sisters, communally raise cubs and hunt. However, this cooperation seems to be density dependent. When resources are limited, group selection favors prides that work together to hunt. When prey is abundant, cooperation is no longer beneficial enough to outweigh the disadvantages of altruism, and hunting is no longer cooperative.

Interactions between different species can also be affected by multilevel selection. Predator-prey relationships can also be affected. Individuals of certain monkey species howl to warn the group of the approach of a predator. The evolution of this trait benefits the group by providing protection, but could be disadvantageous to the individual if the howling draws the predator's attention to them. By affecting these interspecific interactions, multilevel and kinship selection can change the population dynamics of an ecosystem.

Attempts have been done to use multilevel selection to explain the evolution of altruistic behavior in terms of quantitative genetics. Increased frequency or fixation of altruistic alleles can be accomplished through kin selection, in which individuals engage in altruistic behavior to promote the fitness of genetically similar individuals such as siblings. However, this can lead to inbreeding depression, which typically lowers the overall fitness of a population. If altruism were to be selected through an emphasis on benefit to the group as opposed to relatedness and benefit to kin, both the altruistic trait and genetic diversity could be preserved. However, relatedness should still remain a key consideration in studies of multilevel selection. Experimentally imposed multilevel selection on Japanese quail was more effective by an order of magnitude on closely related kin groups than on randomized groups of individuals.

MLS theory can be used to evaluate the balance between group selection and individual selection in specific cases. An experiment by William Muir compared egg productivity in hens, showing that a hyper-aggressive strain had been produced through individual selection, leading to many fatal attacks after only six generations; by implication, it could be argued that group selection must have been acting to prevent this in real life.

Evidence supporting MLS in human society
Some scientific studies have been used to support the multilevel selection theory in humans. David Sloan Wilson has published several collaborative studies. He collaborated with economists on several workshops and a special issue of the Journal of Economic Behavior and Organization on economics and public policy. He asserts that "higher level selection is the invisible hand" of the market. "When higher-level selection doesn't operate, the society ceases to function as a collective unit."

D.S. Wilson also studied neighborhoods in Binghamton, N.Y. to study altruistic or prosocial behavior based on high school tests correlated with a number of other measures of prosocial behavior, but he states that "experiments such as this one are suggestive but seldom definitive."

Peter Turchin developed a field of study called cliodynamics based on the study of cultures, societies, and empires using the principles of group evolution. A peer reviewed journal is concerned with this study. His discussion included an analysis of the rise and fall of the Roman Republic and the Roman Empire, and successive empires that arose in Europe and Asia. He argues that empires rose in areas of metaethnic frontiers, in which different cultures are geographically close and come into conflict. The conflict forces the people in similar cultures to form cooperative alliances that are the precursors to empires. A key factor is asabiya, social cohesion that leads to cooperation and alliances, a term that he credits to Ibn Khaldun (1332-1406), an Arabian historian. Turchin also considers the history of the United States of America and the causes of the American Civil War.

Copied from Nurture Kinship page with minor editing: Anthropologists have worked on an alternative explanation to kin selection from studies of human culture that involves nurture kinship. Holland's Social Bonding and Nurture Kinship discusses biological inclusive fitness theory. The expression of social traits in primates and humans doesn't necessarily depend on conditions of genetic relatedness. For the vast majority of social mammals—including primates and humans—the formation of social bonds (and the resulting social cooperation) are based on familiarity from an early developmental stage. Genetic relatedness is not necessary for the attachment bonds to develop, and it is the performance of nurture that underlies such bonds and the enduring social cooperation that typically accompanies them. The nurture kinship perspective leads to the synthesis of evolutionary biology, psychology, and socio-cultural anthropology on the topic of social bonding and cooperation, without reductionism or positing a deterministic role to genes or genetic relatedness in the mechanisms through which social behaviors are expressed.

The 'nurture kinship' perspective does not necessarily mean that human non-blood relationships such as the relationships based on nurturing are more important than the ones based on blood-kinship. Herbert Gintis, in his review of the book Sex at Dawn, critiques the idea that human males were unconcerned with parentage, "which would make us unlike any other species I can think of".

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Niall Ferguson proposed a modified idea about selection in which he proposed that history can be explained by the evolution of human networks. He wrote, "Man, with his unrivaled neural network, was born to network." He describes networks in this way: "Social networks are the structures that human beings naturally form, beginning with knowledge itself and the various forms of representation that we use to communicate it, as well of course as family trees to which we all necessarily belong...." Ferguson's study is concerned with networks of people that transfer knowledge and specific information that was involved in the examples that he discusses. John Gray in a review of the book was not convinced. He wrote, "He offers a mix of metaphor and what purports to be a new science."

There are other practical areas of human interactions that involve cooperation within groups but competition between different groups, called social cohesion. For example, team building involves exercises to improve group cooperation. Business development is an effort to develop better or more effective companies, or study the reasons that some companies are better than others, in a free market with competition against other companies. These fields of studies are usually based on practical factors, and only rarely are they based on evolutionary theory. According to Turchin, "Although externally corporations brutally compete in the free market, their internal workings rely not on market forces, but on group solidarity!"

Discussions and disagreements
Main proponents in popularizations of the MLS theory are David Sloan Wilson and E.O. Wilson. E. O. Wilson wrote, "The key to the mystery is the force that lifted prehuman social behavior to the human level. The leading candidate is multilevel selection, by which hereditary social behavior improves the competitive ability not just of individuals within groups but among groups as a whole." David Sloan Wilson wrote, "Regardless of whether a phenotypic trait is genetically inherited, learned, or culturally derived, it can spread by virtue of benefitting individuals in the same group, by benefitting all individuals in a group compared to other groups, and so on for a multilevel hierarchy of groups."

Richard Dawkins and other advocates of the gene-centered view of evolution remain unconvinced about group selection. In particular, Dawkins suggests that group selection fails to make an appropriate distinction between replicators and vehicles.

The evolutionary biologist Jerry Coyne summarized the arguments in The New York Times in non-technical terms as follows:

"Group selection isn't widely accepted by evolutionists for several reasons. First, it's not an efficient way to select for traits, like altruistic behavior, that are supposed to be detrimental to the individual but good for the group.... Group selection for altruism would be unlikely to override the tendency of each group to quickly lose its altruists through natural selection favoring cheaters. Further, little evidence exists that selection on groups has promoted the evolution of any trait. Finally, other, more plausible evolutionary forces, like direct selection on individuals for reciprocal support, could have made humans prosocial. These reasons explain why only a few biologists, like [David Sloan] Wilson and E. O. Wilson (no relation), advocate group selection as the evolutionary source of cooperation."

The psychologist Steven Pinker concluded in an essay in Edge.org that group selection has no useful role, and it is a poor implementation of evolutionary theory.

However, following Pinker's essay, there is a lively conversation over this theory from the point of view of experts in several specialties. Some controversial issues are in the following sections.

Poor definitions of terms
Pinker asserted that the term "group selection" is confusing because it has been used in many different ways, to refer to different phenomena, without a clear consensus on the definition. At times, it is simply used to refer to a trait that members of a group have in common, even though there is no connection between the trait in each individual. Sometimes the term is used to describe genetic evolution in different words.

Michael E. Price agreed that using the same terms for biological and cultural evolution may increase confusion between the two processes.

John Tooby agreed that group selection has been used in ways with different and conflicting meanings.

A requirement of any scientific theory is a clear theoretical definition or operational definition of the terms so that everyone who studies the field can understand what is being referred to.

Random vs. acquired variation
Pinker maintains that variations in natural section must be random. Peter Richerson wrote that cultural evolution inherently includes acquired variation that is learned by individuals. For cultural evolution to have any meaning, the variations must be nonrandom. For Richerson, the important point is that the variations are heritable, not that they are random.

Freeman Dyson has even advocated directed genetic modifications, for example for colonizing other planets. He wrote, "One possibility is that groups of parents will be able to give birth to genetically modified children, hoping to give them advantages in the game of life."

Altruism or other related terminology
The question of altruistic actions is a thorny issue in philosophy, as well as in relation to group selection. Pinker points out, "Many forms of real-world altruism provide no advantage in group-against-group competition–particularly compassion for the weak and needy, who are drags on military effectiveness and should be the first to be thrown overboard."

David Sloan Wilson responded to Pinker by writing that "the total gene pool depends upon the relative strength of within- vs. between-group selection." But he also had difficulties in defining the word "altruistic" and began using the term "prosocial."

Jonathan Haidt commented on a study carried out by Muzafer Sherif, who brought two groups of twelve-year-old boys to a summer camp in a state park in Oklahoma in 1954 at which they spontaneously competed with each other, called the Robber's Cave experiment. "Were these acts [by groups of boys] altruistic? Technically yes, because each tribal behavior had some cost for the individual, and it benefited the group's cohesiveness or effectiveness. But I think the opposite of selfishness in evolutionary terms should not always be altruism. For the purposes of the present debate, things get clearer if we contrast selfishness with groupishness... Mental mechanisms that encourage individuals to do things that help their team succeed, despite some cost to the self, are the most likely candidates for having come down to us by a path in which group-selection played a part."

Peter Turchin used an alternate term, asabiya, defined as the capacity of a social group for concerted collective action, credited to ibn Khaldun, the Arab historian. Robert D. Putnam and others use the term social capital. Putnam credits the ideas back to Alexis de Tocqueville, but the first use of the term social capital is credited to L. J. Hanifan. Turchin wrote that "social capital is asabiya for modern democratic societies," but he prefers the term asabiya. But he also wrote that asabiya as he defines it is a prerequisite for a complex society, not a product of an economy.

Punishment and reward
Individuals in groups are faced with punishments and rewards from other members in the group, depending on how their actions benefit the group. According to David Sloan Wilson, "Part of our evolved human nature is to regard predatory interactions within our groups as immoral and to try to suppress them.... Neuroimaging studies show that people who become morally indignant take pleasure in seeking revenge." Punishment and revenge "motivates behaviors that count as altruistic in terms of time, energy, and risk required to punish wrongdoing."

Pinker points out that punishment and reward can be viewed in a framework of reciprocity, so that each individual obtains cooperation from others as long as each prevents being taken advantage of and remembers who reciprocates. Pinker asserts that most altruism can be explained by kinship or by reciprocity. "Nepotistic altruism in humans consists of feelings of warmth, solidarity, and tolerance toward those who are likely to be one's kin." He suggests that other actions that look like altruism actually exploitation, slavery, or deception.

Joseph Henrich responded, "I predict that deception and manipulation, as evolutionary strategies, have serious limitations (they are frequency dependent), especially in a world with multiple social groups, since they will cause natural selection to favor avoidance, group dissolution, and social disengagement."

Robert Boyd and Sarah Mathew pointed out that a major difference between humans and other animals is that humans have a cultural system for punishing rule breakers. "As long as the cost of being punished exceeds the cost of following the norm, obeying the norm will be self-interested. Third-party punishment is absent in other animals, and in humans it is virtually always regulated by culturally transmitted norms. What gets you a good reputation depends on the content of these norms."

Nicolas Baumard added, "According to group selection, punishment evolved as a way to curb selfishness or, as utilitarian philosophers would put it, to deter futures crimes. By contrast, individual selection predicts that punishment is just a way to compensate the victim or, as contractualist philosophers would put it, to restore fairness..."

Michael E. Price wrote, Individuals in groups "are frequently deeply interested in the success of their group, because membership in a successful group can be the best means for an individual to acquire resources and status; as they cooperate, they are preoccupied with whether they are being sufficiently compensated with these rewards."

Joseph Henrich wrote, "People from societies with larger populations, more market integration and more anonymous roles were more prosocial and ready to punish unfairness, not less. In fact, people from the smallest-scale societies sometimes showed no willingness to punish."

Kinds of information
Information in group selection can be transmitted by culture rather than genetics. Pinker explained, "Most of the group-wide traits that group selectionists try to explain are cultural rather than genetic. They are traits that are propagated culturally, such as religious beliefs, social norms, and forms of political organization. Modern group selectionists are often explicit that it is cultural traits they are talking about."

Richard Dawkins coined the term "meme" to describe an "element of culture" or unit of information that is replicated from brain to brain, but he has left studies of memes to other authors such as Susan Blackmore. In some ways, memes are analogous to genes, and memes must cooperate to form a functional culture. In other ways, memes operate in a separate medium for transmitting information, and the properties of information transmission are different from genes. Blackmore wrote, "To fully understand human behaviour, we must consider both genetic and memetic selection." She also pointed out, "Genes and memes are both replicators but otherwise they are different. The analogy between genes and memes has led many people astray and will probably continue to do so for a long time to come."

Studies of human history
Pinker wrote, "Natural selection could legitimately apply to groups if they met certain conditions: the groups made copies of themselves by budding or fissioning, the descendant groups faithfully reproduced traits of the parent group (which cannot be reduced to the traits of their individual members)." As a particular case, he pointed out that he would expect the Roman Empire to form baby Roman Empires.

Peter Turchin did a detailed explanation of European history, and he explained how the European countries indeed descended with variation from the Roman Empire. In particular, his explanation is that each generation of new empires arose on a metaethnic frontier, a region of conflict between two different cultures that don't understand each other. These conflicts force cooperation on the members of the culture to defend themselves.

Robert Boyd and Sarah Mathew wrote, "The great majority human societies lack written records. Understanding how culturally transmitted norms and institutions have shaped human social life requires generalizing, preferably mathematical, theory that can generate predictions that can be compared to the broad patterns in the archaeological and ethnographic records."

Joseph Henrich added, "This body of theory is currently driving the assembly of a vast historical database, which will allow even greater quantitative testing of cultural evolutionary theories. Thus, Pinker's claim that carefully specifying and analyzing the causal processes underlying historical change (which include inter-group competition) and testing these ideas across times and places, [adds] 'nothing to conventional history,' is like saying genetic evolutionary theory adds nothing to butterfly collecting."

Mathematical modeling
Joseph Henrich stated that cultural evolution has been successfully mathematically modeled. He wrote, "By combining psychology with social interaction, these models are designed to improve our understanding of otherwise complex historical processes." "In what way is cultural evolution a metaphorical extension of genetic evolution? It's not. It's standard-issue science that involves the construction of a class of simple models as a means to glean insights into complex processes."

David C. Queller wrote, "Modern group selection theory is as mathematically rigorous as individual selection or inclusive fitness theory. I say this despite being someone who favors the inclusive fitness approach and whose entire career has been based on it.   I think of these less as alternative theories that make different predictions than as two different languages describing the same world."

A discussion of mathematical modeling of society called social physics is used to model the interactions of individual people and their collective behavior.

Development of human morality
Another philosophical problem with human evolution is the question of the development of morality, which is well developed in humans compared to animals. E. O. Wilson suggests that morality is dependent on group selection. He wrote, "Human beings are prone to be moral—do the right thing, hold back, give aid to others, sometimes even at personal risk—because natural selection has favored those interactions of group members benefitting the group as a whole."

Herbert Gintis wrote, "The past few decades have seen the massive accumulation of evidence in favor of the view that human beings are inherently moral creatures, and that morality is not a simple cultural veneer. Humans are born with a moral sense as well with a predisposition to accept and internalize moral norms their society, and often to act on these moral precepts at personal cost.... Gene-culture coevolution provides a plausible scenario for the development a moral sense in humans, a quality that appears to be absent or extremely rudimentary in other species. "

Nicolas Baumard added, "The debate is not between a theory that predicts that humans are moral (group selection) and a theory that predicts they are not (individual selection), but between two theories of morality: one based on sacrifice for the group and the other one based on individual interests. This debate is not novel and echoes a fundamental question in moral philosophy: Is morality about maximizing the welfare of the community or about respecting individual rights?"

Pinker wrote in his rebuttal, "My point of course was not to deny that humans are social or moral or cultural but to show that group selection is unnecessary to explain these obvious facts. That is because living in groups and sharing its accumulated know-how can benefit individuals, so one can explain all the zoologically unusual traits of Homo sapiens using conventional gene-selection theories."

Group selection as an alternative view of evolution
David Queller pointed out, "Pinker is correct that multilevel selection results can usually be seen as restating things we already knew in a different language. But I am loath to say that just because I speak English, others cannot speak in (as homage to Peter Kropotkin) Russian."

Joseph Henrich wrote, "In many cases (though not all), the exact same process can be represented and developed using quite different evolutionary accounting systems.  These accounting systems include (1) individual fitness, (2) inclusive fitness, and (3) multi-level or "group" selection....  It's certainly true that often one can figure out how to use any of these three accounting systems to solve a simple problem, and they give the same answer (about equilibrium states). However, it is NOT true that all three  are equally easy to apply to any given problem. It is also not true that all methods generate the same kinds of insights or understandings about the evolutionary dynamics or equilibrium states. Which accounting system is best entirely depends on the problem and the assumptions one is willing to make in obtaining an answer." He continues by discussing the advantage of using polar coordinates for analyzing the motion of satellites, because it is much easier to use those coordinates than rectangular, cartesian coordinates. He adds, "Why would we remove an analytical tool from our toolbox?"

John Tooby, in spite if criticism of the term group selection, lists seven items that he thinks evolutionary behaviorists can agree on, and he concludes his comments by writing, "I continue to hope that the creative people working in this area may discover important new insights about humans using multilevel selection theory or cultural group selection theory."

Pinker concludes his rebuttal by summarizing a "new" model of group selection. "'In most models of the new group selection, a group is defined as any subset of interacting individuals, that is, as organisms which interact with one another more intensely than they interact with organisms selected from the population at random. Two sisters who help each other, for example, or a pair of friends who trade favors, are dubbed 'a group' It's not hard to see how such 'groups' would be favored by natural selection over pairs of individuals who let each other drown or starve.... Any advantage of [the model of] group selection (in this new sense) would have to come from the models' being more convenient, elegant, simple, transparent, explanatory, or mathematically tractable.... One can separate the benefits that accrue to the entire group (including me) and whatever benefits or costs are assumed by me but no one else in the group. According to group selectionists, this formulation perspicuously explains the evolution of altruism because it includes cases in which a benefactor to the group suffers in comparison to his groupmates; the payoff trickling down from the group's benefit can exceed the cost he pays within the group....  The within-group fitness of these self-sacrificing individuals would be lower than their comrades who selfishly look out for themselves, yet if battles were frequent and decisive enough, the jackpot of victory or the catastrophe of defeat in the competition between groups level could have outweighed the disadvantage of self-sacrifice in the competition within groups. Therefore humans were selected to make sacrifices on behalf of their coalitions, and models of group selection that distinguish within- and between-group fitnesses can transparently explain the evolution of human altruism, including generosity, empathy, sharing, bravery, and civic-mindedness.'"

This model seems consistent with those proposed by proponents of group selection such as David Sloan Wilson and E. O. Wilson. It appear that after this discussion there will be room for agreement and progress. Pinker himself is an advocate for rational progress.

There are many different kinds of problems to solve in the field of evolutionary biology. It is important to have as many methods and approaches as possible to solve them in the most direct ways.