Kin selection
Encyclopedia
Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection. In the "The Origin of Species", he wrote clearly about altruistic sterile social insects that
In this passage "the family" and "stock" stand for a kin group. These passages and others by Darwin about "kin selection" are highlighted and justly celebrated in D.J. Futuyma's textbook of reference "Evolutionary Biology" [(3rd edit.p595) ] and in E.O Wilson's "Sociobiology" [25th edit.p117-118].
The earliest mathematically formal treatments of kin selection were by R.A. Fisher in 1930 and J. B. S. Haldane
in 1932 and 1955. Later on, in works published in 1963 and—most importantly—in 1964, W. D. Hamilton
popularized the concept and the more thorough mathematical treatment given to it by George Price
. The term "kin selection" may first have been coined by John Maynard Smith
in 1964 when he wrote:
Kin selection refers to changes in gene
frequency across generations that are driven at least in part by interactions between related individuals, and this forms much of the conceptual basis of the theory of social evolution
. Indeed, some cases of evolution
by natural selection
can only be understood by considering how biological relatives influence one another'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 behavior, may nonetheless increase in frequency, because relatives often carry the same gene; this is the fundamental principle behind the theory of kin selection. According to the theory, the enhanced fitness of relatives can at times more than compensate for the fitness loss incurred by the individuals displaying the behaviour. As such, this is a special case of a more general model, called inclusive fitness
(in that inclusive fitness refers simply to gene copies in other individuals, without requiring that they be kin). However the validity of this analysis has recently been challenged.
where
This inequality is known as Hamilton's rule after W. D. Hamilton
who published, in 1964, the first formal quantitative treatment of kin selection to deal with the evolution
of apparently altruistic acts.
Originally, the definition for relatedness (r) in Hamilton's rule was explicitly given as Sewall Wright
's coefficient of relationship
: the probability
that at a random locus
, the allele
s there will be identical by descent (Hamilton 1963, American Naturalist, p. 355). Subsequent authors, including Hamilton, sometimes reformulate this with a regression
, which, unlike probabilities, can be negative, and so it is possible for individuals to be negatively related, which simply means that two individuals can be less genetically alike than two random ones on average (Hamilton 1970, Nature & Grafen 1985 Oxford Surveys in Evolutionary Biology). This has been invoked to explain the evolution of spite
ful behaviours. Spiteful behavior defines an act (or acts) that results in harm, or loss of fitness, to both the actor and the recipient.
In the 1930s J.B.S. Haldane had full grasp of the basic quantities and considerations that play a role in kin selection. He famously said that, "I would lay down my life for two brothers or eight cousins
". Kin altruism is the term for altruistic behaviour whose evolution is supposed to have been driven by kin selection.
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.
In 2011, experimentalists found empirically that Hamilton's rule describes very accurately the conditions under which altruism emerged in simulated populations of foraging robots. The accuracy of this first quantitative corroboration of Hamilton's rule is all the more impressive given that Hamilton's model made several simplifications that did not apply to the foraging robots.
.
Hamilton (1964) outlined two ways in which kin selection altruism
could be favoured.
Kin Recognition: Firstly, if individuals have the capacity to recognize kin (kin recognition
) and to adjust their behaviour on the basis of kinship (kin discrimination), then the average relatedness of the recipients of altruism could be high enough for this to be favoured. Because of the facultative nature of this mechanism, it is generally regarded that kin recognition and discrimination are unimportant except among 'higher' forms of life (although there is some evidence for this mechanism among protozoa
). A special case of the kin recognition/discrimination mechanism is the hypothetical 'green beard'
, where a gene for social behaviour also causes a distinctive phenotype that can be recognised by other carriers of the gene. Hamilton's discussion of greenbeard altruism serves as an illustration that relatedness is a matter of genetic similarity and that this similarity is not necessarily caused by genealogical closeness (kinship).
Viscous Populations: Secondly, even indiscriminate altruism may be favoured in so-called viscous populations, i.e. those characterized by low rates or short ranges of dispersal. Here, social partners are typically genealogically close kin, and so altruism may be able to flourish even in the absence of kin recognition and kin discrimination faculties—spatial proximity serves as a rudimentary form of discrimination. This suggests a rather general explanation for altruism. Directional selection will always favor those with higher rates of fecundity within a certain population. Social individuals can often ensure the survival of their own kin by participating in, and following the rules of a group (assuming the implied faculties for group discrimination).
These mechanisms explain a relatively high r between interacting individuals. Absolute genetic similarity is not a measure of r; rather, r shows the “excess” relatedness between an actor and a recipient compared with the relatedness between an actor and a random member of the population. Thus, in a clonal population with 100% genetic similarity, r = 0 (as strange as that may sound). This is because there can be no correlation between genetic similarity and interaction strengths if genetic similarity is constant.
It has often been observed that altruism cannot be maintained in a population of randomly interacting individuals (see Michod [1982] and references therein). In such a population, the correlation between genetic similarity and interaction strength is necessarily absent, thus r = 0 and rB < C for any C > 0. This is why mechanisms such as spatial structure and kin recognition are so important for the long-term stability of altruistic traits, and why measures such as "population-wide average r" are meaningless in the absence of such mechanisms.
, following Darwinian anthropologists' interpretation of kin selection theory initially attempted to explain human altruistic behavior through kin selection by stating that “behaviors that help a genetic relative are favored by natural selection.” However, most Evolutionary psychologists recognize that this common short-hand formulation is inaccurate;
Nevertheless, evolutionary psychologists argue that, an overwhelming amount of empirical evidence corroborating human kin selection has been found, using different methods of study.. 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; that human kinship patterns are not necessarily built upon blood-ties. An alternative approach is to observe how Hamilton's own perspective developed;
Hamilton's later refinements of his theory thus demonstrated that it does not simply predict that genetically related individuals will inevitably recognise and engage in positive social behaviours with genetic relatives. 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). 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. 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.
Eusociality
(true sociality) is used to describe social systems with three characteristics: one is an overlap in generations between parents and their offspring, two is cooperative brood care, and the third characteristic is specialized castes of nonreproductive individuals. Social insects
are an excellent example of organisms that display presumed 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, and 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 behavior in such organisms (see Eusociality
).
Another example is preference amount individuals in sun-tailed monkey
communities. Data shows that maternal kin (kin related to by mothers) behaved more preferentially towards each other. However, once kin got beyond half-siblings or further relatives, this bias dropped significantly.
Alarm calls in ground squirrels are another example. While they may alert others of the same species to danger, they draw attention to the caller and expose it to increased risk of predation. Paul Sherman, of Cornell University, studied the alarm calls of ground squirrels. He observed that they occurred most frequently when the caller had relatives nearby. In a similar study, John Hoogland was able to follow individual males through different stages of life. He found that the male prairie dogs modified their rate of calling when closer to kin. These behaviors show that self-sacrifice is directed towards close relatives and that there is an indirect fitness gain.
Alan Krakauer of University of California, Berkeley
has studied kin selection in the courtship behavior of wild turkeys. Like a teenager helping her older sister prepare for prom night, a subordinate turkey may help his dominant brother put on an impressive team display that is only of direct benefit to the dominant member.
Recent studies provide evidence that even certain plants can recognize and respond to kinship ties. Using sea rocket for her experiments, Susan Dudley at McMaster University
in 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.
In human fertilization
, some sperm cells consume their acrosome
prematurely on the surface of the egg cell, facilitating for surrounding sperms, having on average 50% genome similarity, to penetrate the egg cell.
In the wood mouse
(), aggregates of spermatozoa form mobile trains, some of the spermatozoa undergo a premature acrosome reactions that correlate to improved mobility of the mobile trains towards the female egg for fertilization. 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.
Experimental studies, interviews, and surveys
A study interviewed several hundred women in Los Angeles to study patterns of helping between kin versus non-kin. 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. 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.
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.
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.
Humans may use the inheritance of material goods and wealth to maximize 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.
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.
Family investment in offspring among black South African households also appears consistent with an inclusive fitness model. 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.
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".
Numerous other studies pertaining to kin selection exist, suggesting how inclusive fitness may work amongst peoples from the Ye’kwana of southern Venezuela to the Gypsies of Hungary to even the doomed Donner Party of the United States. Various secondary sources provide compilations of kin selection studies.
and EO Wilson. The authors argue 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's criticisms aroused a hostile response from a large section of the evolutionary biology community, including one reply published in Nature with over 100 authors.
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 characterized has been slaughtered, but the breeder has gone with confidence to the same stock and has succeeded" [www.classicreader.com/book/107/59/]
In this passage "the family" and "stock" stand for a kin group. These passages and others by Darwin about "kin selection" are highlighted and justly celebrated in D.J. Futuyma's textbook of reference "Evolutionary Biology" [(3rd edit.p595) ] and in E.O Wilson's "Sociobiology" [25th edit.p117-118].
The earliest mathematically formal treatments of kin selection were by R.A. Fisher in 1930 and J. B. S. Haldane
J. B. S. Haldane
John Burdon Sanderson Haldane FRS , known as Jack , was a British-born geneticist and evolutionary biologist. A staunch Marxist, he was critical of Britain's role in the Suez Crisis, and chose to leave Oxford and moved to India and became an Indian citizen...
in 1932 and 1955. Later on, in works published in 1963 and—most importantly—in 1964, W. D. Hamilton
W. D. Hamilton
William Donald Hamilton FRS was a British evolutionary biologist, widely recognised as one of the greatest evolutionary theorists of the 20th century....
popularized the concept and the more thorough mathematical treatment given to it by George Price
George R. Price
George Robert Price was an American population geneticist. Originally a physical chemist and later a science journalist, he moved to London in 1967, where he worked in theoretical biology at the Galton Laboratory, making three important contributions: first, rederiving W.D...
. The term "kin selection" may first have been coined by John Maynard Smith
John Maynard Smith
John Maynard Smith,His surname was Maynard Smith, not Smith, nor was it hyphenated. F.R.S. was a British theoretical evolutionary biologist and geneticist. Originally an aeronautical engineer during the Second World War, he took a second degree in genetics under the well-known biologist J.B.S....
in 1964 when he wrote:
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.
Kin selection refers to changes in gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
frequency across generations that are driven at least in part by interactions between related individuals, and this forms much of the conceptual basis of the theory of social evolution
Social evolution
Social evolution is a subdiscipline of evolutionary biology that is concerned with social behaviors that have fitness consequences for individuals other than the actor...
. Indeed, some cases of evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
by natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
can only be understood by considering how biological relatives influence one another's fitness
Fitness (biology)
Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
. Under natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
, a gene encoding a trait that enhances the fitness of each individual carrying it should increase in frequency within the population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
; 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 behavior, may nonetheless increase in frequency, because relatives often carry the same gene; this is the fundamental principle behind the theory of kin selection. According to the theory, the enhanced fitness of relatives can at times more than compensate for the fitness loss incurred by the individuals displaying the behaviour. As such, this is a special case of a more general model, called inclusive fitness
Inclusive fitness
In evolutionary biology and evolutionary psychology, the inclusive fitness of an organism is the sum of its classical fitness and the number of equivalents of its own offspring it can add to the population by supporting others...
(in that inclusive fitness refers simply to gene copies in other individuals, without requiring that they be kin). However the validity of this analysis has recently been challenged.
Hamilton's rule
Formally, such genes should increase in frequency whenwhere
- 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 locusLocus (genetics)In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...
is identical by descent. - B = the additional reproductive benefit gained by the recipient of the altruistic act,
- C = the reproductive cost to the individual of performing the act.
This inequality is known as Hamilton's rule after W. D. Hamilton
W. D. Hamilton
William Donald Hamilton FRS was a British evolutionary biologist, widely recognised as one of the greatest evolutionary theorists of the 20th century....
who published, in 1964, the first formal quantitative treatment of kin selection to deal with the evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
of apparently altruistic acts.
Originally, the definition for relatedness (r) in Hamilton's rule was explicitly given as Sewall Wright
Sewall Wright
Sewall Green Wright was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. With R. A. Fisher and J.B.S. Haldane, he was a founder of theoretical population genetics. He is the discoverer of the inbreeding coefficient and of...
's coefficient of relationship
Coefficient of relationship
In population genetics, Sewall Wright's coefficient of relationship or coefficient of relatedness or relatedness or r is defined as 2 times the Coefficient of Inbreeding...
: the probability
Probability
Probability is ordinarily used to describe an attitude of mind towards some proposition of whose truth we arenot certain. The proposition of interest is usually of the form "Will a specific event occur?" The attitude of mind is of the form "How certain are we that the event will occur?" The...
that at a random locus
Locus (genetics)
In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...
, the allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s there will be identical by descent (Hamilton 1963, American Naturalist, p. 355). Subsequent authors, including Hamilton, sometimes reformulate this with a regression
Regression analysis
In statistics, regression analysis includes many techniques for modeling and analyzing several variables, when the focus is on the relationship between a dependent variable and one or more independent variables...
, which, unlike probabilities, can be negative, and so it is possible for individuals to be negatively related, which simply means that two individuals can be less genetically alike than two random ones on average (Hamilton 1970, Nature & Grafen 1985 Oxford Surveys in Evolutionary Biology). This has been invoked to explain the evolution of spite
Spite
In fair division problems, spite is a phenomenon that occurs when a player's value of an allocation decreases when one or more other players' valuation increases...
ful behaviours. Spiteful behavior defines an act (or acts) that results in harm, or loss of fitness, to both the actor and the recipient.
In the 1930s J.B.S. Haldane had full grasp of the basic quantities and considerations that play a role in kin selection. He famously said that, "I would lay down my life for two brothers or eight cousins
Cousin chart
In kinship terminology, a cousin is a relative with whom one shares one or more common ancestors. The term is rarely used when referring to a relative in one's immediate family where there is a more specific term . The term "blood relative" can be used synonymously and establishes the existence of...
". Kin altruism is the term for altruistic behaviour whose evolution is supposed to have been driven by kin selection.
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.
In 2011, experimentalists found empirically that Hamilton's rule describes very accurately the conditions under which altruism emerged in simulated populations of foraging robots. The accuracy of this first quantitative corroboration of Hamilton's rule is all the more impressive given that Hamilton's model made several simplifications that did not apply to the foraging robots.
Mechanisms
An altruistic case is one where the instigating individual suffers a fitness loss while the receiving individual benefits by a fitness gain. The sacrifice of one individual to help another is an example of altruismAltruism
Altruism is a concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions, though the concept of 'others' toward whom concern should be directed can vary among cultures and religions. Altruism is the opposite of...
.
Hamilton (1964) outlined two ways in which kin selection altruism
Altruism
Altruism is a concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions, though the concept of 'others' toward whom concern should be directed can vary among cultures and religions. Altruism is the opposite of...
could be favoured.
Kin Recognition: Firstly, if individuals have the capacity to recognize kin (kin recognition
Kin recognition
Kin recognition is animals' abilities to distinguish between close genetic kin and non-kin. In evolutionary biology and in psychology, such capabilities are presumed to have evolved to serve the adaptive functions of kin altruism and inbreeding avoidance...
) and to adjust their behaviour on the basis of kinship (kin discrimination), then the average relatedness of the recipients of altruism could be high enough for this to be favoured. Because of the facultative nature of this mechanism, it is generally regarded that kin recognition and discrimination are unimportant except among 'higher' forms of life (although there is some evidence for this mechanism among protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
). A special case of the kin recognition/discrimination mechanism is the hypothetical 'green beard'
Green-beard effect
The gene-centered view of evolution postulates that natural selection will increase the frequency of those genes whose phenotypic effects ensure their successful replication...
, where a gene for social behaviour also causes a distinctive phenotype that can be recognised by other carriers of the gene. Hamilton's discussion of greenbeard altruism serves as an illustration that relatedness is a matter of genetic similarity and that this similarity is not necessarily caused by genealogical closeness (kinship).
Viscous Populations: Secondly, even indiscriminate altruism may be favoured in so-called viscous populations, i.e. those characterized by low rates or short ranges of dispersal. Here, social partners are typically genealogically close kin, and so altruism may be able to flourish even in the absence of kin recognition and kin discrimination faculties—spatial proximity serves as a rudimentary form of discrimination. This suggests a rather general explanation for altruism. Directional selection will always favor those with higher rates of fecundity within a certain population. Social individuals can often ensure the survival of their own kin by participating in, and following the rules of a group (assuming the implied faculties for group discrimination).
These mechanisms explain a relatively high r between interacting individuals. Absolute genetic similarity is not a measure of r; rather, r shows the “excess” relatedness between an actor and a recipient compared with the relatedness between an actor and a random member of the population. Thus, in a clonal population with 100% genetic similarity, r = 0 (as strange as that may sound). This is because there can be no correlation between genetic similarity and interaction strengths if genetic similarity is constant.
It has often been observed that altruism cannot be maintained in a population of randomly interacting individuals (see Michod [1982] and references therein). In such a population, the correlation between genetic similarity and interaction strength is necessarily absent, thus r = 0 and rB < C for any C > 0. This is why mechanisms such as spatial structure and kin recognition are so important for the long-term stability of altruistic traits, and why measures such as "population-wide average r" are meaningless in the absence of such mechanisms.
Kin selection and human social patterns
Evolutionary psychologistsEvolutionary psychology
Evolutionary psychology is an approach in the social and natural sciences that examines psychological traits such as memory, perception, and language from a modern evolutionary perspective. It seeks to identify which human psychological traits are evolved adaptations, that is, the functional...
, following Darwinian anthropologists' interpretation of kin selection theory initially attempted to explain human altruistic behavior through kin selection by stating that “behaviors that help a genetic relative are favored by natural selection.” However, most Evolutionary psychologists recognize that this common short-hand formulation is inaccurate;
Nevertheless, evolutionary psychologists argue that, an overwhelming amount of empirical evidence corroborating human kin selection has been found, using different methods of study.. 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; that human kinship patterns are not necessarily built upon blood-ties. An alternative approach is to observe how Hamilton's own perspective developed;
Hamilton's later refinements of his theory thus demonstrated that it does not simply predict that genetically related individuals will inevitably recognise and engage in positive social behaviours with genetic relatives. 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). 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. 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.
Examples
Eusociality
Eusociality is a term used for the highest level of social organization in a hierarchical classification....
(true sociality) is used to describe social systems with three characteristics: one is an overlap in generations between parents and their offspring, two is cooperative brood care, and the third characteristic is specialized castes of nonreproductive individuals. Social insects
Eusociality
Eusociality is a term used for the highest level of social organization in a hierarchical classification....
are an excellent example of organisms that display presumed 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, and Hamilton's rule is presumed to be satisfied because the benefits in fitness
Fitness (biology)
Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
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 behavior in such organisms (see Eusociality
Eusociality
Eusociality is a term used for the highest level of social organization in a hierarchical classification....
).
Another example is preference amount individuals in sun-tailed monkey
Sun-tailed Monkey
The sun-tailed monkey , also known as the sun-tailed guenon, is a primate that lives semi-terrestrially in one hilly area of moist evergreen forest in Gabon....
communities. Data shows that maternal kin (kin related to by mothers) behaved more preferentially towards each other. However, once kin got beyond half-siblings or further relatives, this bias dropped significantly.
Alarm calls in ground squirrels are another example. While they may alert others of the same species to danger, they draw attention to the caller and expose it to increased risk of predation. Paul Sherman, of Cornell University, studied the alarm calls of ground squirrels. He observed that they occurred most frequently when the caller had relatives nearby. In a similar study, John Hoogland was able to follow individual males through different stages of life. He found that the male prairie dogs modified their rate of calling when closer to kin. These behaviors show that self-sacrifice is directed towards close relatives and that there is an indirect fitness gain.
Alan Krakauer of University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
has studied kin selection in the courtship behavior of wild turkeys. Like a teenager helping her older sister prepare for prom night, a subordinate turkey may help his dominant brother put on an impressive team display that is only of direct benefit to the dominant member.
Recent studies provide evidence that even certain plants can recognize and respond to kinship ties. Using sea rocket for her experiments, Susan Dudley at McMaster University
McMaster University
McMaster University is a public research university whose main campus is located in Hamilton, Ontario, Canada. The main campus is located on of land in the residential neighbourhood of Westdale, adjacent to Hamilton's Royal Botanical Gardens...
in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
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.
In human fertilization
Human fertilization
Human fertilization is the union of a humanoid egg and sperm, usually occurring in the ampulla of the uterine tube. The result of this union is the production of a zygote, or fertilized egg, initiating prenatal development...
, some sperm cells consume their acrosome
Acrosome
The acrosome is an organelle that develops over the anterior half of the head in the spermatozoa of many animals. It is a cap-like structure derived from the Golgi apparatus. Acrosome formation is completed during testicular maturation. In Eutherian mammals the acrosome contains digestive enzymes...
prematurely on the surface of the egg cell, facilitating for surrounding sperms, having on average 50% genome similarity, to penetrate the egg cell.
In the wood mouse
Wood mouse
The wood mouse is a common murid rodent from Europe and northwestern Africa. It is closely related to the yellow-necked mouse but differs in that it has no band of yellow fur around the neck, has slightly smaller ears, and is usually slightly smaller overall: around 90 mm in length...
(), aggregates of spermatozoa form mobile trains, some of the spermatozoa undergo a premature acrosome reactions that correlate to improved mobility of the mobile trains towards the female egg for fertilization. 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.
Human examples
Whether or not Hamilton's rule always applies, studies have demonstrated that relatedness is often important for human altruism in that humans are inclined to behave more altruistically toward kin than toward unrelated individuals. Many people choose to live near relatives, exchange sizable gifts with relatives, and favor relatives in wills in proportion to their relatedness.Experimental studies, interviews, and surveys
A study interviewed several hundred women in Los Angeles to study patterns of helping between kin versus non-kin. 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. 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.
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.
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.
Humans may use the inheritance of material goods and wealth to maximize 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.
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.
Family investment in offspring among black South African households also appears consistent with an inclusive fitness model. 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.
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".
Numerous other studies pertaining to kin selection exist, suggesting how inclusive fitness may work amongst peoples from the Ye’kwana of southern Venezuela to the Gypsies of Hungary to even the doomed Donner Party of the United States. Various secondary sources provide compilations of kin selection studies.
Criticism
The theory of kin selection has had a profound impact on interpretations of genetic evolution of eusociality but it has been recently criticized by Martin NowakMartin Nowak
Martin A. Nowak is Professor of Biology and Mathematics and Director of the Program for Evolutionary Dynamics at Harvard University.-Career:Martin Nowak studied biochemistry and mathematics at the University of Vienna, and earned his Ph. D. in 1989, working with Peter Schuster on quasi-species...
and EO Wilson. The authors argue 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's criticisms aroused a hostile response from a large section of the evolutionary biology community, including one reply published in Nature with over 100 authors.
See also
- AltruismAltruismAltruism is a concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions, though the concept of 'others' toward whom concern should be directed can vary among cultures and religions. Altruism is the opposite of...
- Ethnic nepotismEthnic nepotismEthnic nepotism describes a human tendency for in-group bias or in-group favouritism applied by nepotism for people with the same ethnicity.- The theory :...
- KinshipKinshipKinship is a relationship between any entities that share a genealogical origin, through either biological, cultural, or historical descent. And descent groups, lineages, etc. are treated in their own subsections....
- Group selectionGroup selectionIn evolutionary biology, group selection refers to the idea that alleles can become fixed or spread in a population because of the benefits they bestow on groups, regardless of the alleles' effect on the fitness of individuals within that group....
- Inclusive fitnessInclusive fitnessIn evolutionary biology and evolutionary psychology, the inclusive fitness of an organism is the sum of its classical fitness and the number of equivalents of its own offspring it can add to the population by supporting others...
- The Selfish GeneThe Selfish GeneThe Selfish Gene is a book on evolution by Richard Dawkins, published in 1976. It builds upon the principal theory of George C. Williams's first book Adaptation and Natural Selection. Dawkins coined the term "selfish gene" as a way of expressing the gene-centred view of evolution as opposed to the...
- The kinship theory of genomic imprintingThe kinship theory of genomic imprintingThe kinship theory of genomic imprinting is an evolutionary account of the origin and evolution of imprinted genes. When two alleles at a diploid locus differ in their optimal gene expression level depending on their parent of origin, the theory predicts the evolutionary outcome to be imprinted...
Further reading
- Queller, D.C. & Strassman, J.E. (2002) Quick Guide: Kin Selection. Current Biology,12,R832.
- West, S.A., Gardner, A. & Griffin, A.S. (2006) Quick Guide: Altruism. Current Biology,16,R482-R483.