Kin selection

From Wikipedia, the free encyclopedia

 

The co-operative behaviour of social insects like the honey bee can be explained by kin selection.

Kin selection is the evolutionary strategy that favours the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Kin altruism can look like altruistic behaviour whose evolution is driven by kin selection. Kin selection is an instance of inclusive fitness, which combines the number of offspring produced with the number an individual can ensure the production of by supporting others, such as siblings.

Charles Darwin discussed the concept of kin selection in his 1859 book, The Origin of Species, where he reflected on the puzzle of sterile social insects, such as honey bees, which leave reproduction to their mothers, arguing that a selection benefit to related organisms (the same "stock") would allow the evolution of a trait that confers the benefit but destroys an individual at the same time. R.A. Fisher in 1930 and J.B.S. Haldane in 1932 set out the mathematics of kin selection, with Haldane famously joking that he would willingly die for two brothers or eight cousins. In 1964, W.D. Hamilton popularised the concept and the major advance in the mathematical treatment of the phenomenon by George R. Price which has become known as Hamilton's rule. In the same year John Maynard Smith used the actual term kin selection for the first time.

According to Hamilton's rule, kin selection causes genes to increase in frequency when the genetic relatedness of a recipient to an actor multiplied by the benefit to the recipient is greater than the reproductive cost to the actor.^[1][2] Hamilton proposed two mechanisms for kin selection. First, kin recognition allows individuals to be able to identify their relatives. Second, in viscous populations, populations in which the movement of organisms from their place of birth is relatively slow, local interactions tend to be among relatives by default. The viscous population mechanism makes kin selection and social cooperation possible in the absence of kin recognition. In this case, nurture kinship, the treatment of individuals as kin as a result of living together, is sufficient for kin selection, given reasonable assumptions about population dispersal rates. Note that kin selection is not the same thing as group selection, where it instead is proposed that natural selection acts on the group as a whole.

In humans, altruism is both more likely and on a larger scale with kin than with unrelated individuals; for example, humans give presents according to how closely related they are to the recipient. In other species, vervet monkeys use allomothering, where related females such as older sisters or grandmothers often care for young, according to their relatedness. The social shrimp Synalpheus regalis protects juveniles within highly related colonies.

Historical overview

Charles Darwin was the first to discuss the concept of kin selection. In The Origin of Species, he wrote clearly about the conundrum represented by altruistic sterile social insects that

This difficulty, though appearing insuperable, is lessened, or, as I believe, disappears, when it is remembered that selection may be applied to the family, as well as to the individual, and may thus gain the desired end. Breeders of cattle wish the flesh and fat to be well marbled together. An animal thus characterised has been slaughtered, but the breeder has gone with confidence to the same stock and has succeeded.

— Darwin^[3]

In this passage "the family" and "stock" stand for a kin group. These passages and others by Darwin about "kin selection" are highlighted in D.J. Futuyma's textbook of reference Evolutionary Biology^[4] and in E. O. Wilson's Sociobiology.^[5]

The earliest mathematically formal treatments of kin selection were by R.A. Fisher in 1930^[6] and J.B.S. Haldane in 1932^[7] and 1955.^[8] J.B.S. Haldane fully grasped the basic quantities and considerations in kin selection, famously writing "I would lay down my life for two brothers or eight cousins".^[9] Haldane's remark alluded to the fact that if an individual loses its life to save two siblings, four nephews, or eight cousins, it is a "fair deal" in evolutionary terms, as siblings are on average 50% identical by descent, nephews 25%, and cousins 12.5% (in a diploid population that is randomly mating and previously outbred). But Haldane also joked that he would truly die only to save more than a single identical twin of his or more than two full siblings.^[10][11] In 1955 he clarified:

Let us suppose that you carry a rare gene that affects your behaviour so that you jump into a flooded river and save a child, but you have one chance in ten of being drowned, while I do not possess the gene, and stand on the bank and watch the child drown. If the child's your own child or your brother or sister, there is an even chance that this child will also have this gene, so five genes will be saved in children for one lost in an adult. If you save a grandchild or a nephew, the advantage is only two and a half to one. If you only save a first cousin, the effect is very slight. If you try to save your first cousin once removed the population is more likely to lose this valuable gene than to gain it. … It is clear that genes making for conduct of this kind would only have a chance of spreading in rather small populations when most of the children were fairly near relatives of the man who risked his life.^[12]

W. D. Hamilton, in 1963^[13] and especially in 1964^[1][2] popularised the concept and the more thorough mathematical treatment given to it by George Price.^[1][2]

John Maynard Smith may have coined the actual term "kin selection" in 1964:

These processes I will call kin selection and group selection respectively. Kin selection has been discussed by Haldane and by Hamilton. … By kin selection I mean the evolution of characteristics which favour the survival of close relatives of the affected individual, by processes which do not require any discontinuities in the population breeding structure.^[14]

Kin selection causes changes in gene frequency across generations, driven by interactions between related individuals. This dynamic forms the conceptual basis of the theory of social evolution. Some cases of evolution by natural selection can only be understood by considering how biological relatives influence each other's fitness. Under natural selection, a gene encoding a trait that enhances the fitness of each individual carrying it should increase in frequency within the population; and conversely, a gene that lowers the individual fitness of its carriers should be eliminated. However, a hypothetical gene that prompts behaviour which enhances the fitness of relatives but lowers that of the individual displaying the behaviour, may nonetheless increase in frequency, because relatives often carry the same gene. According to this principle, the enhanced fitness of relatives can at times more than compensate for the fitness loss incurred by the individuals displaying the behaviour, making kin selection possible. This is a special case of a more general model, "inclusive fitness".^[15] This analysis has been challenged,^[16] Wilson writing that "the foundations of the general theory of inclusive fitness based on the theory of kin selection have crumbled"^[17] and that he now relies instead on the theory of eusociality and "gene-culture co-evolution" for the underlying mechanics of sociobiology.

"Kin selection" should not be confused with "group selection" according to which a genetic trait can become prevalent within a group because it benefits the group as a whole, regardless of any benefit to individual organisms. All known forms of group selection conform to the principle that an individual behaviour can be evolutionarily successful only if the genes responsible for this behaviour conform to Hamilton's Rule, and hence, on balance and in the aggregate, benefit from the behaviour.^[18][19][20]

Hamilton's rule

Formally, genes should increase in frequency when

${\displaystyle rB>C}$

where

r=the genetic relatedness of the recipient to the actor, often defined as the probability that a gene picked randomly from each at the same locus is identical by descent.

B=the additional reproductive benefit gained by the recipient of the altruistic act,

C=the reproductive cost to the individual performing the act.

This inequality is known as Hamilton's rule after W. D. Hamilton who in 1964 published the first formal quantitative treatment of kin selection.

The relatedness parameter (r) in Hamilton's rule was introduced in 1922 by Sewall Wright as a coefficient of relationship that gives the probability that at a random locus, the alleles there will be identical by descent.^[21] Subsequent authors, including Hamilton, sometimes reformulate this with a regression, which, unlike probabilities, can be negative. A regression analysis producing statistically significant negative relationships indicates that two individuals are less genetically alike than two random ones (Hamilton 1970, Nature & Grafen 1985 Oxford Surveys in Evolutionary Biology). This has been invoked to explain the evolution of spiteful behaviour consisting of acts that result in harm, or loss of fitness, to both the actor and the recipient.

Several scientific studies have found that the kin selection model can be applied to nature. For example, in 2010 researchers used a wild population of red squirrels in Yukon, Canada to study kin selection in nature. The researchers found that surrogate mothers would adopt related orphaned squirrel pups but not unrelated orphans. The researchers calculated the cost of adoption by measuring a decrease in the survival probability of the entire litter after increasing the litter by one pup, while benefit was measured as the increased chance of survival of the orphan. The degree of relatedness of the orphan and surrogate mother for adoption to occur depended on the number of pups the surrogate mother already had in her nest, as this affected the cost of adoption. The study showed that females always adopted orphans when rB > C, but never adopted when rB < C, providing strong support for Hamilton's rule.^[22]

Mechanisms

Altruism occurs where the instigating individual suffers a fitness loss while the receiving individual experiences a fitness gain. The sacrifice of one individual to help another is an example.^[23]

Hamilton (1964) outlined two ways in which kin selection altruism could be favoured:

The selective advantage which makes behaviour conditional in the right sense on the discrimination of factors which correlate with the relationship of the individual concerned is therefore obvious. It may be, for instance, that in respect of a certain social action performed towards neighbours indiscriminately, an individual is only just breaking even in terms of inclusive fitness. If he could learn to recognise those of his neighbours who really were close relatives and could devote his beneficial actions to them alone an advantage to inclusive fitness would at once appear. Thus a mutation causing such discriminatory behaviour itself benefits inclusive fitness and would be selected. In fact, the individual may not need to perform any discrimination so sophisticated as we suggest here; a difference in the generosity of his behaviour according to whether the situations evoking it were encountered near to, or far from, his own home might occasion an advantage of a similar kind." (1996 [1964], 51)^[1]

Kin recognition: theory predicts that bearers of a trait (like the fictitious 'green beard') will behave altruistically towards others with the same trait.

Kin recognition: First, if individuals have the capacity to recognise kin and to discriminate (positively) on the basis of kinship, then the average relatedness of the recipients of altruism could be high enough for kin selection. Because of the facultative nature of this mechanism, kin recognition and discrimination are expected to be unimportant except among 'higher' forms of life such as the fish Neolamprologus pulcher (although there is some evidence for it among protozoa). Note also that kin recognition may be selected for inbreeding avoidance, and little evidence indicates that 'innate' kin recognition plays a role in mediating altruism. A thought experiment on the kin recognition/discrimination distinction is the hypothetical 'green beard', where a gene for social behaviour is imagined also to cause a distinctive phenotype that can be recognised by other carriers of the gene. Due to conflicting genetic similarity in the rest of the genome, there would be selection pressure for green-beard altruistic sacrifices to be suppressed, making common ancestry the most likely form of inclusive fitness.

Viscous populations: Secondly, even indiscriminate altruism may be favoured in "viscous" populations with low rates or short ranges of dispersal. Here, social partners are typically genealogically close kin, and so altruism can flourish even in the absence of kin recognition and kin discrimination faculties—spatial proximity and circumstantial cues serving as a rudimentary form of discrimination. This suggests a rather general explanation for altruism. Directional selection always favours those with higher rates of fecundity within a certain population. Social individuals can often enhance the survival of their own kin by participating in and following the rules of their own group.

Hamilton later modified his thinking to suggest that an innate ability to recognise actual genetic relatedness was unlikely to be the dominant mediating mechanism for kin altruism:

But once again, we do not expect anything describable as an innate kin recognition adaptation, used for social behaviour other than mating, for the reasons already given in the hypothetical case of the trees. (Hamilton 1987, 425)^[24]

Hamilton's later clarifications often go unnoticed, and because of the long-standing assumption that kin selection requires innate powers of kin recognition, some theorists have tried to clarify the position in recent work:

In his original papers on inclusive fitness theory, Hamilton pointed out a sufficiently high relatedness to favour altruistic behaviours could accrue in two ways — kin discrimination or limited dispersal (Hamilton, 1964, 1971,1972, 1975). There is a huge theoretical literature on the possible role of limited dispersal reviewed by Platt & Bever (2009) and West et al. (2002a), as well as experimental evolution tests of these models (Diggle et al., 2007; Griffin et al., 2004; Kümmerli et al., 2009). However, despite this, it is still sometimes claimed that kin selection requires kin discrimination (Oates & Wilson, 2001; Silk, 2002 ). Furthermore, a large number of authors appear to have implicitly or explicitly assumed that kin discrimination is the only mechanism by which altruistic behaviours can be directed towards relatives... [T]here is a huge industry of papers reinventing limited dispersal as an explanation for cooperation. The mistakes in these areas seem to stem from the incorrect assumption that kin selection or indirect fitness benefits require kin discrimination (misconception 5), despite the fact that Hamilton pointed out the potential role of limited dispersal in his earliest papers on inclusive fitness theory (Hamilton, 1964; Hamilton, 1971; Hamilton, 1972; Hamilton, 1975). (West et al. 2010, p.243 and supplement)^[25]

The assumption that kin recognition must be innate, and that cue-based mediation of social cooperation based on limited dispersal and shared developmental context are not sufficient, has obscured significant progress made in applying kin selection and inclusive fitness theory to a wide variety of species, including humans,^[26][27] on the basis of cue-based mediation of social bonding and social behaviours.

Kin selection and human social patterns

Families are important in human behaviour, but kin selection may be based on closeness and other cues.

Evolutionary psychologists, following early human sociobiologists' interpretation^[28] of kin selection theory initially attempted to explain human altruistic behaviour through kin selection by stating that "behaviors that help a genetic relative are favored by natural selection." However, most Evolutionary psychologists recognise that this common shorthand formulation is inaccurate;

[M]any misunderstandings persist. In many cases, they result from conflating "coefficient of relatedness" and "proportion of shared genes," which is a short step from the intuitively appealing—but incorrect—interpretation that "animals tend to be altruistic toward those with whom they share a lot of genes." These misunderstandings don’t just crop up occasionally; they are repeated in many writings, including undergraduate psychology textbooks—most of them in the field of social psychology, within sections describing evolutionary approaches to altruism. (Park 2007, p860)^[29]

As with the earlier sociobiological forays into the cross-cultural data, typical approaches are not able to find explanatory fit with the findings of ethnographers insofar that human kinship patterns are not necessarily built upon blood-ties. However, as Hamilton's later refinements of his theory make clear, it does not simply predict that genetically related individuals will inevitably recognise and engage in positive social behaviours with genetic relatives: rather, indirect context-based mechanisms may have evolved, which in historical environments have met the inclusive fitness criterion (see above section). Consideration of the demographics of the typical evolutionary environment of any species is crucial to understanding the evolution of social behaviours. As Hamilton himself puts it, "Altruistic or selfish acts are only possible when a suitable social object is available. In this sense behaviours are conditional from the start." (Hamilton 1987, 420).^[24]

Under this perspective, and noting the necessity of a reliable context of interaction being available, the data on how altruism is mediated in social mammals is readily made sense of. In social mammals, primates and humans, altruistic acts that meet the kin selection criterion are typically mediated by circumstantial cues such as shared developmental environment, familiarity and social bonding.^[30] That is, it is the context that mediates the development of the bonding process and the expression of the altruistic behaviours, not genetic relatedness per se. This interpretation thus is compatible with the cross-cultural ethnographic data^[27] and has been called nurture kinship.

Examples

Eusociality (true sociality) is used to describe social systems with three characteristics: an overlap in generations between parents and their offspring, cooperative brood care, and specialised castes of non-reproductive individuals.^[31] The social insects provide good examples of organisms with what appear to be kin selected traits. The workers of some species are sterile, a trait that would not occur if individual selection was the only process at work. The relatedness coefficient r is abnormally high between the worker sisters in a colony of Hymenoptera due to haplodiploidy. Hamilton's rule is presumed to be satisfied because the benefits in fitness for the workers are believed to exceed the costs in terms of lost reproductive opportunity, though this has never been demonstrated empirically. There are competing hypotheses, as well, which may also explain the evolution of social behaviour in such organisms.^[16]
 

Sun-tailed monkeys favour their own maternal kin.

In sun-tailed monkey communities, maternal kin (kin related to by mothers) favour each other, but that with relatives more distant than half-siblings, this bias drops significantly.^[32]

Alarm calls in ground squirrels appear to confirm kin selection. While calls may alert others of the same species to danger, they draw attention to the caller and expose it to increased risk of predation. The calls occur most frequently when the caller had relatives nearby.^[33] Individual male prairie dogs followed through different stages of life modify their rate of calling when closer to kin. These behaviours show that self-sacrifice is directed towards close relatives, and that there is an indirect fitness gain.^[31] Surrogate mothers adopt orphaned red squirrels in the wild only when the conditions of Hamilton's rule were met.^[22]

Alan Krakauer of University of California, Berkeley has studied kin selection in the courtship behaviour of wild turkeys. Like a teenager helping her older sister prepare for a party, a subordinate turkey may help his dominant brother put on an impressive team display that is only of direct benefit to the dominant member.^[34]

Even certain plants can recognise and respond to kinship ties. Using sea rocket, Susan Dudley at McMaster University, Canada compared the growth patterns of unrelated plants sharing a pot to plants from the same clone. She found that unrelated plants competed for soil nutrients by aggressive root growth. This did not occur with sibling plants.^[35]

In the wood mouse (Apodemus sylvaticus), aggregates of spermatozoa form mobile trains, some of the spermatozoa undergo premature acrosome reactions that correlate to improved mobility of the mobile trains towards the female egg for fertilisation. This association is thought to proceed as a result of a "green beard effect" in which the spermatozoa perform a kin-selective altruistic act after identifying genetic similarity with the surrounding spermatozoa.^[36]

In humans

Whether or not Hamilton's rule always applies, relatedness is often important for human altruism, in that humans are inclined to behave more altruistically toward kin than toward unrelated individuals.^[37] Many people choose to live near relatives, exchange sizeable gifts with relatives, and favour relatives in wills in proportion to their relatedness.^[37]

Experimental studies, interviews, and surveys

Interviews of several hundred women in Los Angeles showed that while non-kin friends were willing to help one another, their assistance was far more likely to be reciprocal. The largest amounts of non-reciprocal help, however, were reportedly provided by kin. Additionally, more closely related kin were considered more likely sources of assistance than distant kin.^[38] Similarly, several surveys of American college students found that individuals were more likely to incur the cost of assisting kin when a high probability that relatedness and benefit would be greater than cost existed. Participants’ feelings of helpfulness were stronger toward family members than non-kin. Additionally, participants were found to be most willing to help those individuals most closely related to them. Interpersonal relationships between kin in general were more supportive and less Machiavellian than those between non-kin.^[39]

In one experiment, the longer participants (from both the UK and the South African Zulus) held a painful skiing position, the more money or food was presented to a given relative. Participants repeated the experiment for individuals of different relatedness (parents and siblings at r=.5, grandparents, nieces, and nephews at r=.25, etc.). The results showed that participants held the position for longer intervals the greater the degree of relatedness between themselves and those receiving the reward.^[40]

Observational studies

A study of food-sharing practices on the West Caroline islets of Ifaluk determined that food-sharing was more common among people from the same islet, possibly because the degree of relatedness between inhabitants of the same islet would be higher than relatedness between inhabitants of different islets. When food was shared between islets, the distance the sharer was required to travel correlated with the relatedness of the recipient—a greater distance meant that the recipient needed to be a closer relative. The relatedness of the individual and the potential inclusive fitness benefit needed to outweigh the energy cost of transporting the food over distance.^[41]

Humans may use the inheritance of material goods and wealth to maximise their inclusive fitness. By providing close kin with inherited wealth, an individual may improve his or her kin’s reproductive opportunities and thus increase his or her own inclusive fitness even after death. A study of a thousand wills found that the beneficiaries who received the most inheritance were generally those most closely related to the will’s writer. Distant kin received proportionally less inheritance, with the least amount of inheritance going to non-kin.^[42]

A study of childcare practices among Canadian women found that respondents with children provide childcare reciprocally with non-kin. The cost of caring for non-kin was balanced by the benefit a woman received—having her own offspring cared for in return. However, respondents without children were significantly more likely to offer childcare to kin. For individuals without their own offspring, the inclusive fitness benefits of providing care to closely related children might outweigh the time and energy costs of childcare.^[43]

Family investment in offspring among black South African households also appears consistent with an inclusive fitness model.^[44] A higher degree of relatedness between children and their caregivers frequently correlated with a higher degree of investment in the children, with more food, health care, and clothing being provided. Relatedness between the child and the rest of the household also positively associated with the regularity of a child’s visits to local medical practitioners and with the highest grade the child had completed in school. Additionally, relatedness negatively associated with a child’s being behind in school for his or her age.

Observation of the Dolgan hunter-gatherers of northern Russia suggested that, while reciprocal food-sharing occurs between both kin and non-kin, there are larger and more frequent asymmetrical transfers of food to kin. Kin are also more likely to be welcomed to non-reciprocal meals, while non-kin are discouraged from attending. Finally, even when reciprocal food-sharing occurs between families, these families are often very closely related, and the primary beneficiaries are the offspring.^[45]

Other research indicates that violence in families is more likely to occur when step-parents are present and that "genetic relationship is associated with a softening of conflict, and people's evident valuations of themselves and of others are systematically related to the parties' reproductive values".^[46]

Numerous other studies suggest how inclusive fitness may work amongst different peoples, such as the Ye’kwana of southern Venezuela, the Gypsies of Hungary, and the doomed Donner Party of the United States.^{[47][48][49][50][51]}

In non-human species

Vervet monkeys display kin selection between siblings, mothers and offspring, and grandparent-grandchild. These monkeys utilise allomothering, where the allomother is typically an older female sibling or a grandmother. Other studies have shown that individuals will act aggressively toward other individuals that were aggressive toward their relatives.^[52][53]

Synalpheus regalis is a eusocial shrimp that protects juveniles in the colony. By defending the young, the large defender shrimp can increase its inclusive fitness. Allozyme data revealed that relatedness within colonies is high, averaging 0.50, indicating that colonies in this species represent close kin groups.^[54]

Objections

The theory of kin selection has been criticised by Alonso in 1998^[55] and by Alonso and Schuck-Paim in 2002.^[56] Alonso and Schuck-Paim argue that the behaviours which kin selection attempts to explain are not altruistic (in pure Darwinian terms) because: (1) they may directly favour the performer as an individual aiming to maximise its progeny (so the behaviours can be explained as ordinary individual selection); (2) these behaviours benefit the group (so they can be explained as group selection); or (3) they are by-products of a developmental system of many "individuals" performing different tasks (like a colony of bees, or the cells of multicellular organisms, which are the focus of selection). They also argue that the genes involved in sex ratio conflicts could be treated as "parasites" of (already established) social colonies, not as their "promoters", and, therefore the sex ratio in colonies would be irrelevant to the transition to eusociality.^[55][56] Those ideas were mostly ignored until they were put forward again in a series of papers by E. O. Wilson, Bert Hölldobler, Martin Nowak and others.^[57][58][59] Nowak, Tarnita and Wilson argued that

Inclusive fitness theory is not a simplification over the standard approach. It is an alternative accounting method, but one that works only in a very limited domain. Whenever inclusive fitness does work, the results are identical to those of the standard approach. Inclusive fitness theory is an unnecessary detour, which does not provide additional insight or information.

— Nowak, Tarnita, and Wilson^[16]

They, like Alonso (1998) and Alonso and Schuck-Paim (2002) earlier, argue for a multi-level selection model instead.^[16] This aroused a strong response, including a rebuttal published in Nature from over a hundred researchers.

Darwinian anthropology

From Wikipedia, the free encyclopedia

Darwinian anthropology describes an approach to anthropological analysis which employs various theories from Darwinian evolutionary biology. Whilst there are a number of areas of research that can come under this broad description (Marks, 2004) some specific research projects have been closely associated with the label. A prominent example is the project that developed in the mid 1970s with the goal of applying sociobiological perspectives to explain patterns of human social relationships, particularly kinship patterns across human cultures.

This kinship-focused Darwinian anthropology was a significant intellectual forebear of evolutionary psychology, and both draw on biological theories of the evolution of social behavior (in particular inclusive fitness theory) upon which the field of sociobiology was founded.

Overview

In 1974 the biologist Richard D. Alexander published an article The Evolution of Social Behavior which drew upon W.D.Hamilton's work on inclusive fitness and kin selection and noted that:

Although ten years have passed since Hamilton's landmark papers, apparently only a single social scientist (Campbell, 31) has made a distinct effort to incorporate kin selection into theories of human altruism... But so have the biologists, for one reason or another, failed to consider the enormous literature on topics like kinship systems and reciprocity in human behavior. (Alexander 1974, 326)^[2]

Amongst other suggestions, Alexander suggested that certain patterns of social cooperation documented by ethnographers, in particular the avunculate ('mother's brother') relationship, could be explained in reference to individuals pursuing a strategy of individual inclusive fitness maximization under conditions of low certainty-of-paternity. This hypothesis was subsequently taken up and elaborated in a series of studies by other Darwinian anthropologists:

The hypothesis follows that matrilineal inheritance is a cultural trait that evolved in response to low probability of paternity. [...] The paternity hypothesis was rescued and made explicit in the context of modern evolutionary theory by Alexander in 1974. Over the next 10 years this provided the impetus leading to numerous theoretical refinements and scholarly and empirical investigations (Flinn 1981; Gaulin & Schlegel 1980; Greene 1978; Hartung 1981b; Kurland 1979).(Hartung 1985,661-663) ^[3]

Ultimately these analyses were considered unsuccessful, and were specifically criticized by other sociobiologists on a number of grounds. One problem was said to be that interpreting inclusive fitness theory to imply that individuals have evolved the characteristic of pursuing strategies to maximize their own 'inclusive fitness' is erroneous; the theory should instead be interpreted to describe selection pressures on genes:

Alexander’s argument... erred through looking at things from the point of view of an individual... I believe this kind of error is all too easy to make when we use the technical term ‘fitness’ [of individuals]. This is why I have avoided using the term in this book. There is really only one entity whose point of view matters in evolution, and that entity is the selfish gene.(Dawkins 1989 (1976), 137 emphasis in original) ^[4]

A related problem was that, in assuming that individuals simply operate as inclusive fitness maximizing agents, any investigation of the proximate psychological mechanisms that mediate social behaviors was ignored. Symons made this observation in his 1989 Critique of Darwinian Anthropology:

DA’s central hypothesis is that “evolved behavioral tendencies” cause human “behavior to assume the form that maximizes inclusive fitness”(Irons 1979b, 33). Turke and Betzig (1985) state this hypothesis as a formal prediction: “Modern Darwinian theory predicts that human behavior will be adaptive, that is, designed to promote maximum reproductive success through available descendant and nondescendant relatives.”(p 79)… [T]he key terms in [this] quotation are used in DA to bypass the question of phenotypic design in characterizations of adaptation.(Symons 1989, 131-132) ^[5]

Symons, along with Tooby and Cosmides, were amongst the founders of the emerging school of evolutionary psychology, whose aim has been to focus more on these hypothesized proximate psychological mechanisms.

Theoretical background

Darwinian anthropology was critiqued by Symonds for its agnosticism as to the psychological mechanisms governing how social behavior is actually expressed in the human species, and its reliance on interpreting inclusive fitness theory to simply imply that humans have evolved to be inclusive fitness maximizers. This section will review some of the relevant background discussion in inclusive fitness theory to clarify why this position was considered untenable.

Evolutionary versus proximate explanations

Inclusive Fitness theory has often been interpreted to mean that social behavior per se is a goal of evolution, and also that genes (or individual organisms) are selected to find ways of actively distinguishing the identity of close genetic relatives ‘in order to’ engage in social behaviors with them.

[M]any misunderstandings persist. In many cases, they result from conflating “coefficient of relatedness” and “proportion of shared genes,” which is a short step from the intuitively appealing—but incorrect—interpretation that “animals tend to be altruistic toward those with whom they share a lot of genes.” These misunderstandings don’t just crop up occasionally; they are repeated in many writings, including undergraduate psychology textbooks—most of them in the field of social psychology, within sections describing evolutionary approaches to altruism. (Park 2007, p860)^[6]

The apparent rationale for this common mis-interpretation is that organisms would thereby benefit the “Inclusive Fitness of the individuals (and genes) involved”. This approach overlooks the point that evolution is not a teleological process, but a passive, consequential and undirected biological process, where environmental variations and drift effects are present alongside random gene mutations and natural selection.

Inclusive fitness theory takes the form of an ultimate explanation, specifically a criterion (br>c), for the evolution of social behaviors, not a proximate mechanism governing the expression of social behaviors. What forms of social behavior might meet this criterion are cannot be a priori specified by the theory, nor can it shed light on whether the life history of a species provides opportunities for social interactions to occur. Thus, strictly speaking, the interpretation that organisms ‘have evolved to’ direct social behavior towards genetic relatives is not implied by the theory (see also inclusive fitness).

Investigating how inclusive fitness theory might apply to the potential emergence of social traits in any given species must begin with an analysis of the evolutionarily typical ecological niche, demographics, and patterns of interaction of that species. Where significant interaction between individuals is not present in the life history of a species, the theory is necessarily null regarding social behaviors between individuals. As Silk (2001) put it;

The role of kinship in the daily lives of animals depends on the demographic composition of the groups in which they live. Kin selection will only be an important force in the evolution of social behavior if animals find themselves in situations where they have an opportunity to fulfill the predictions of Hamilton’s rule. At a minimum, kin must be available. The number, availability, and degree of relatedness among kin will depend on how groups are constructed in nature.” (Silk 2001, 77)^[7]

Consideration must thus be given to whether the ecological niche leads to the clustering of individuals in groups or whether individuals are typically solitary. Socioecology research, for example, suggests that fundamental influences on demographic patterns are the distribution/fecundity of primary food sources as well as patterns of predation. When considering social behavior traits of a given species, consideration of these influences is in a sense, logically prior to analyses of inclusive fitness pressures on the species.

Selection pressure on genes or strategy of individuals

Darwinian anthropology, following R. D. Alexander, used the notion of the inclusive fitness of individuals rather than the inclusive fitness of genes. Dawkins (above) pointed to this as an error. The source of the confusion can be traced to discussions in Hamilton's early papers on inclusive fitness. In his 1963 paper Hamilton refers, unambiguously, to selection pressures on genes;

[T]he ultimate criterion which determines whether G [a gene] will spread is not whether the behaviour is to the benefit of the behaver but whether it is to the benefit of the gene G; and this will be the case if the average net result of the behaviour is to add to the gene pool a handful of genes containing G in higher concentration than does the gene pool itself.” (1996 [1963], 7)^[8]

However, in his paper published in 1964, actually written before the 1963 paper (Hamilton 1996), Hamilton had included a subsidiary discussion on what the genetic theory might imply for how we look at the fitness of individuals:

Actually, in the preceding mathematical account we were not concerned with the inclusive fitness of individuals as described here but rather with certain averages of them which we call the inclusive fitness of types. But the idea of the inclusive fitness of an individual is nevertheless a useful one. Just as in the sense of classical selection we may consider whether a given character expressed in an individual is adaptive in the sense of being in the interest of his personal fitness or not, so in the present sense of selection we may consider whether the character or trait of behaviour is or is not adaptive in the sense if being in the interest of his inclusive fitness.” (Hamilton 1996 [1964], 38)^[9]

It is clear here that the formal treatment is of the selection pressures on types (genes or traits), whilst the notion of individual inclusive fitness may serve as a guide to the adaptiveness of the trait; just as consideration of effects of a trait on an individual's fitness can be instructive when considering classical selection on traits. At the same time, it is understandable that Alexander took the inclusive fitness of individuals as a heuristic device.

Context-based or discrimination-based expression mechanisms

In his 1964 paper, Hamilton 'hazards' “the following unrigorous statement of the main principle that has emerged from the model”;

The Social behaviour of a species evolves in such a way that in each distinct behaviour-evoking situation the individual will seem to value his neighbours’ fitness against his own according to the coefficients of relationship appropriate to that situation.”(1964 [1996], 49)^[9]

He uses the terms 'hazards', 'unrigorous', and 'will seem' deliberately, since his formal analysis makes clear that the model specifies the evolutionary selection pressure, rather than specifying what mechanisms govern the proximate expression of social behaviors. He also clearly points to social behaviors being evoked in distinct situations, and that individuals may encounter potential social recipients of different degree of relationship in different situations. If one ignores the cautious qualifying words however, the passage might readily be interpreted to imply that individuals are indeed expected to make an active assessment of the degree of relatedness of others they interact with in different situations. Later in the paper, Hamilton again discusses the issue of whether the performance (or expression) of social behaviors might be conditional on; (a) discriminating factors which correlate with close relationship with the recipient, or (b) actually discriminating which individuals 'really are' in close relationship with the recipient:

The selective advantage which makes behaviour conditional in the right sense on the discrimination of factors which correlate with the relationship of the individual concerned is therefore obvious. It may be, for instance, that in respect of a certain social action performed towards neighbours indiscriminately, an individual is only just breaking even in terms of inclusive fitness. If he could learn to recognise those of his neighbours who really were close relatives and could devote his beneficial actions to them alone an advantage to inclusive fitness would at once appear. Thus a mutation causing such discriminatory behaviour itself benefits inclusive fitness and would be selected. In fact, the individual may not need to perform any discrimination so sophisticated as we suggest here; a difference in the generosity of his behaviour according to whether the situations evoking it were encountered near to, or far from, his own home might occasion an advantage of a similar kind.” (1996 [1964], 51)^[9]

For certain social behaviors, Hamilton suggests there may be selection pressure for more discerning discrimination of genetic relatedness, were the mutation to occur. But 'in fact' the same net result of accurately targeting social behaviors towards genetic relatives could be achieved via a simpler mechanism of being expressed in proximity to the actor's 'home'. Hamilton is thus agnostic as to whether evolved social behaviors might be expressed via straightforward proximate mechanisms such as location-based cues, or whether more specific discriminatory powers might govern their expression. He does suggest that the distinct social contexts within which various social behaviors are expressed are factors to consider. Other theorists have discussed these questions of whether proximity, context or more discriminatory expression may govern behaviors:

Animals cannot, of course, be expected to know, in a cognitive sense, who their relatives are, and in practice the behaviour that is favoured by natural selection will be equivalent to a rough rule of thumb such as ‘share food with anything that moves in the nest in which you are sitting.’ If families happen to go around in groups, this fact provides a useful rule of thumb for kin selection: ‘care for any individual you often see’.” (Dawkins 1979, 187)^[10]

If, for example, animals behave with an equal degree of altruism to all their “neighbours”… and if on average animals are related to their neighbours, then I would regard this as an example of kin selection. It is not a necessary feature of kin selection that an animal should distinguish different degrees of relationship among its neighbours, and behave with greater altruism to the more closely related…”(Maynard Smith 1976, 282 emphasis in original)^[11]

Dawkins believes social behaviors will in practice be governed by context-based expression. Maynard Smith is, like Hamilton, agnostic, but reiterates the point that context-based cues might well govern their expression and that actively distinguishing relatives is not necessarily expected for the expression of those social traits whose evolution is governed by inclusive fitness criteria. In sum, inclusive fitness theory does imply that; the evolutionary emergence of social behavior can occur where there is statistical association of genes between social actors and recipients; but that the expression of such evolved social behaviors is not necessarily governed by actual genetic relatedness between participants. The evolutionary criterion and the proximate mechanism must thus not be confused: the first does require genetic association (of the form br>c), the second does not.
Darwinian anthropology's central premise that human behavior has evolved to maximize the inclusive fitness of individuals is thus not a logical derivative of the theory. Also, the notion that humans will discriminate social behaviors towards genetic relatives is again not entailed by the theory.

Reception by anthropologists

Before the questions raised within anthropology about the study of ‘kinship’ by Schneider ^[12] and others from the 1960s onwards, anthropology itself had paid very little attention to the notion that social bonds were anything other than connected to consanguinal (or genetic) relatedness (or its local cultural conceptions). The social bonding associated with provision of and sharing of food was one important exception, particularly in the work of Richards,^[13] but this was largely ignored by descriptions of ‘kinship’ till more recently. Although questioning the means by which ‘kinship bonds’ form, few of these early accounts questioned the fundamental role of ‘procreative ties’ in social bonding (Schneider, 1984). From the 1950s onwards, reports on kinship patterns in the New Guinea Highlands added some momentum to what had until then been only occasional fleeting suggestions that living together (co-residence) might underlie social bonding, and eventually contributed to the general shift away from a genealogical approach. For example, on the basis of his observations, Barnes suggested:

[C]learly, genealogical connexion of some sort is one criterion for membership of many social groups. But it may not be the only criterion; birth, or residence, or a parent’s former residence, or utilization of garden land, or participation in exchange and feasting activities or in house-building or raiding, may be other relevant criteria for group membership.”(Barnes 1962,6)^[14]

Similarly, Langness' ethnography of the Bena Bena also emphasized a break with the genealogical perspective:

The sheer fact of residence in a Bena Bena group can and does determine kinship. People do not necessarily reside where they do because they are kinsmen: rather they become kinsmen because they reside there.” (Langness 1964, 172 emphasis in original)^[15]

By 1972, Schneider^[16][17] had raised deep problems with the notion that human social bonds and 'kinship' was a natural category built upon genealogical ties (for more information, see kinship), and especially in the wake of his 1984 critique^[12] this has become broadly accepted by most, if not all, anthropologists.^[18]

The darwinian anthropology (and other sociobiological) perspectives, arising in the early 1970s, had not unreasonably assumed that the genealogical conceptions of human kinship, in place since Morgan's early work^[19] in the 1870s, were still valid as a universal feature of humans. But they emerged at precisely the time that anthropology, being particularly sensitive about its own apparent 'ethnocentric' generalizations about kinship (from cultural particulars to human universals) was seeking to distance itself from these conceptions. The vehemence of Sahlins' rebuttal of sociobiology's genetic relatedness perspective in his 1976 The use and abuse of Biology, which underlined the non-genealogical nature of human kinship, can be understood as part of this 'distancing' trend.

Alternative approaches

The lack of success of darwinian anthropology created space for alternative approaches to analyzing human social behaviors from a biological perspective. Alexander's initial point (above) that the inclusive fitness framework had been scarcely applied to human kinship and social patterns has remained largely valid. But the move away from genealogical kinship in anthropology has continued to be a major barrier to any potential resolution. This section reviews a range of approaches to synthesizing ideas from evolutionary biology to observations and data about human social behaviour across contemporary human populations. Whilst some of these approaches include the inclusive fitness approach, others may seek to demonstrate fit to other theories from evolutionary biology, or to demonstrate that certain proximate mechanisms of social behaviour are both compatible with the inclusive fitness approach, and also with the broad variety of ethnographic data on human kinship patterns.

Criticism

Theories in evolutionary biology relevant to understanding social behavior may not be limited to frameworks such as inclusive fitness theory. The theory of reciprocal altruism may have equal or greater explanatory power for some forms of human social behavior, and perhaps kinship patterns. Other approaches may maintain that human behavior is less amenable to biological analysis due to the prominent influence of social learning and cultural transmission in the human species, and instead advance ideas based on the role of e.g. culture, historical contingencies or economic/environmental conditions. All or any of these may or may not contribute valuable insights to our understanding of social behavior and social patterns in humans.

Sociobiology

From Wikipedia, the free encyclopedia

Sociobiology is a field of biology that aims to examine and explain social behavior in terms of evolution. It draws from disciplines including ethology, anthropology, evolution, zoology, archaeology, and population genetics. Within the study of human societies, sociobiology is closely allied to Darwinian anthropology, human behavioral ecology and evolutionary psychology.

Sociobiology investigates social behaviors such as mating patterns, territorial fights, pack hunting, and the hive society of social insects. It argues that just as selection pressure led to animals evolving useful ways of interacting with the natural environment, so also it led to the genetic evolution of advantageous social behavior.

While the term "sociobiology" originated at least as early as the 1940s, the concept did not gain major recognition until the publication of E. O. Wilson's book Sociobiology: The New Synthesis in 1975. The new field quickly became the subject of controversy. Critics, led by Richard Lewontin and Stephen Jay Gould, argued that genes played a role in human behavior, but that traits such as aggressiveness could be explained by social environment rather than by biology. Sociobiologists responded by pointing to the complex relationship between nature and nurture.

Definition

E. O. Wilson defined sociobiology as "the extension of population biology and evolutionary theory to social organization".^[1]

Sociobiology is based on the premise that some behaviors (social and individual) are at least partly inherited and can be affected by natural selection. It begins with the idea that behaviors have evolved over time, similar to the way that physical traits are thought to have evolved. It predicts that animals will act in ways that have proven to be evolutionarily successful over time. This can, among other things, result in the formation of complex social processes conducive to evolutionary fitness.

The discipline seeks to explain behavior as a product of natural selection. Behavior is therefore seen as an effort to preserve one's genes in the population. Inherent in sociobiological reasoning is the idea that certain genes or gene combinations that influence particular behavioral traits can be inherited from generation to generation^[2]

For example, newly dominant male lions often kill cubs in the pride that they did not sire. This behavior is adaptive because killing the cubs eliminates competition for their own offspring and causes the nursing females to come into heat faster, thus allowing more of his genes to enter into the population. Sociobiologists would view this instinctual cub-killing behavior as being inherited through the genes of successfully reproducing male lions, whereas non-killing behavior may have died out as those lions were less successful in reproducing.^[3]

History

E. O. Wilson, a central figure in the history of sociobiology, from the publication in 1975 of his book Sociobiology: The New Synthesis

The ethologist John Paul Scott coined the word sociobiology at a 1948 conference on genetics and social behaviour,^[4] and it became widely used after it was popularized by Edward O. Wilson in his 1975 book, Sociobiology: The New Synthesis. However, the influence of evolution on behavior has been of interest to biologists and philosophers since soon after the discovery of evolution itself. Peter Kropotkin's Mutual Aid: A Factor of Evolution, written in the early 1890s, is a popular example. Antecedents of modern sociobiological thinking can be traced to the 1960s and the work of such biologists as Richard D. Alexander, Robert Trivers and William D. Hamilton. The idea of the inheritance of behaviour arose from J. B. S. Haldane's idea about how "altruistic behaviour" (see Altruism) could be passed from generation to generation.^[5] Wilson's book pioneered and popularized the attempt to explain the evolutionary mechanics behind social behaviors such as altruism, aggression, and nurturance, primarily in ants (Wilson's own research specialty) and other Hymenoptera, but also in other animals.^[6] The final chapter of the book is devoted to sociobiological explanations of human behavior, and Wilson later wrote a Pulitzer Prize winning book, On Human Nature, that addressed human behavior specifically.^[7]

Edward H. Hagen writes in The Handbook of Evolutionary Psychology that sociobiology is, despite the public controversy regarding the applications to humans, "one of the scientific triumphs of the twentieth century." "Sociobiology is now part of the core research and curriculum of virtually all biology departments, and it is a foundation of the work of almost all field biologists" Sociobiological research on nonhuman organisms has increased dramatically and continuously in the world's top scientific journals such as Nature and Science. The more general term behavioral ecology is commonly substituted for the term sociobiology in order to avoid the public controversy.^[8]

Theory

Sociobiologists believe that human behavior, as well as nonhuman animal behavior, can be partly explained as the outcome of natural selection. They contend that in order to fully understand behavior, it must be analyzed in terms of evolutionary considerations.

Natural selection is fundamental to evolutionary theory. Variants of hereditary traits which increase an organism's ability to survive and reproduce will be more greatly represented in subsequent generations, i.e., they will be "selected for". Thus, inherited behavioral mechanisms that allowed an organism a greater chance of surviving and/or reproducing in the past are more likely to survive in present organisms. That inherited adaptive behaviors are present in nonhuman animal species has been multiply demonstrated by biologists, and it has become a foundation of evolutionary biology. However, there is continued resistance by some researchers over the application of evolutionary models to humans, particularly from within the social sciences, where culture has long been assumed to be the predominant driver of behavior.

Nikolaas Tinbergen, whose work influenced sociobiology.

Sociobiology is based upon two fundamental premises:

• Certain behavioral traits are inherited,
• Inherited behavioral traits have been honed by natural selection. Therefore, these traits were probably "adaptive" in the environment in which the species evolved.

Sociobiology uses Nikolaas Tinbergen's four categories of questions and explanations of animal behavior. Two categories are at the species level; two, at the individual level. The species-level categories (often called "ultimate explanations") are

• the function (i.e., adaptation) that a behavior serves and
• the evolutionary process (i.e., phylogeny) that resulted in this functionality.

The individual-level categories (often called "proximate explanations") are

• the development of the individual (i.e., ontogeny) and
• the proximate mechanism (e.g., brain anatomy and hormones).

Sociobiologists are interested in how behavior can be explained logically as a result of selective pressures in the history of a species. Thus, they are often interested in instinctive, or intuitive behavior, and in explaining the similarities, rather than the differences, between cultures. For example, mothers within many species of mammals – including humans – are very protective of their offspring. Sociobiologists reason that this protective behavior likely evolved over time because it helped the offspring of the individuals which had the characteristic to survive. This parental protection would increase in frequency in the population. The social behavior is believed to have evolved in a fashion similar to other types of nonbehavioral adaptations, such as a coat of fur, or the sense of smell.

Individual genetic advantage fails to explain certain social behaviors as a result of gene-centred selection. E.O. Wilson argued that evolution may also act upon groups.^[9] The mechanisms responsible for group selection employ paradigms and population statistics borrowed from evolutionary game theory. Altruism is defined as "a concern for the welfare of others". If altruism is genetically determined, then altruistic individuals must reproduce their own altruistic genetic traits for altruism to survive, but when altruists lavish their resources on non-altruists at the expense of their own kind, the altruists tend to die out and the others tend to increase. An extreme example is a soldier losing his life trying to help a fellow soldier. This example raises the question of how altruistic genes can be passed on if this soldier dies without having any children.^[10]

Within sociobiology, a social behavior is first explained as a sociobiological hypothesis by finding an evolutionarily stable strategy that matches the observed behavior. Stability of a strategy can be difficult to prove, but usually, it will predict gene frequencies. The hypothesis can be supported by establishing a correlation between the gene frequencies predicted by the strategy, and those expressed in a population.

Altruism between social insects and littermates has been explained in such a way. Altruistic behavior, behavior that increases the reproductive fitness of others at the apparent expense of the altruist,^[11] in some animals has been correlated to the degree of genome shared between altruistic individuals. A quantitative description of infanticide by male harem-mating animals when the alpha male is displaced as well as rodent female infanticide and fetal resorption are active areas of study. In general, females with more bearing opportunities may value offspring less, and may also arrange bearing opportunities to maximize the food and protection from mates.

An important concept in sociobiology is that temperament traits exist in an ecological balance. Just as an expansion of a sheep population might encourage the expansion of a wolf population, an expansion of altruistic traits within a gene pool may also encourage increasing numbers of individuals with dependent traits.

Studies of human behavior genetics have generally found behavioral traits such as creativity, extroversion, aggressiveness, and IQ have high heritability. The researchers who carry out those studies are careful to point out that heritability does not constrain the influence that environmental or cultural factors may have on those traits.^[12][13]

Criminality is actively under study, but extremely controversial. There are arguments that in some environments criminal behavior might be adaptive.^[14] The novelist Elias Canetti also has noted applications of sociobiological theory to cultural practices such as slavery and autocracy.^[15]

Support for premise

Genetic mouse mutants illustrate the power that genes exert on behaviour. For example, the transcription factor FEV (aka Pet1), through its role in maintaining the serotonergic system in the brain, is required for normal aggressive and anxiety-like behavior.^[16] Thus, when FEV is genetically deleted from the mouse genome, male mice will instantly attack other males, whereas their wild-type counterparts take significantly longer to initiate violent behaviour. In addition, FEV has been shown to be required for correct maternal behaviour in mice, such that offspring of mothers without the FEV factor do not survive unless cross-fostered to other wild-type female mice.^[17]

A genetic basis for instinctive behavioural traits among non-human species, such as in the above example, is commonly accepted among many biologists; however, attempting to use a genetic basis to explain complex behaviours in human societies has remained extremely controversial.^[18][19]

Reception

Steven Pinker argues that critics have been overly swayed by politics and a fear of biological determinism,^[a] accusing among others Stephen Jay Gould and Richard Lewontin of being "radical scientists", whose stance on human nature is influenced by politics rather than science,^[21] while Lewontin, Steven Rose and Leon Kamin who drew a distinction between the politics and history of an idea and its scientific validity^[22] argue that sociobiology fails on scientific grounds. Gould grouped sociobiology with eugenics, criticizing both in his book The Mismeasure of Man.^[23]

Noam Chomsky has expressed views on sociobiology on several occasions. During a 1976 meeting of the Sociobiology Study Group, as reported by Ullica Segerstråle, Chomsky argued for the importance of a sociobiologically informed notion of human nature.^[24] Chomsky argued that human beings are biological organisms and ought to be studied as such, with his criticism of the "blank slate" doctrine in the social sciences (which would inspire a great deal of Steven Pinker's and others' work in evolutionary psychology), in his 1975 Reflections on Language.^[25] Chomsky further hinted at the possible reconciliation of his anarchist political views and sociobiology in a discussion of Peter Kropotkin's Mutual Aid: A Factor of Evolution, which focused more on altruism than aggression, suggesting that anarchist societies were feasible because of an innate human tendency to cooperate.^[26]

Wilson has claimed that he had never meant to imply what ought to be, only what is the case. However, some critics have argued that the language of sociobiology readily slips from "is" to "ought",^[22] an instance of the naturalistic fallacy. Pinker has argued that opposition to stances considered anti-social, such as ethnic nepotism, is based on moral assumptions, meaning that such opposition is not falsifiable by scientific advances.^[27] The history of this debate, and others related to it, are covered in detail by Cronin (1993), Segerstråle (2000), and Alcock (2001).