Trauma model of mental disorders

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The trauma model of mental disorders, or trauma model of psychopathology, emphasises the effects of physical, sexual and psychological trauma as key causal factors in the development of psychiatric disorders, including depression and anxiety as well as psychosis, whether the trauma is experienced in childhood or adulthood. It conceptualises victims as having understandable reactions to traumatic events rather than suffering from mental illness.

Trauma models emphasise that traumatic experiences are more common and more significant in terms of aetiology than has often been thought in people diagnosed with mental disorders. Such models have their roots in some psychoanalytic approaches, notably Sigmund Freud's early ideas on childhood sexual abuse and hysteria, Pierre Janet's work on dissociation, and Bowlby's attachment theory. There is significant research supporting the linkage between early experiences of chronic maltreatment and severe neglect and later psychological problems.

In the 1960s trauma models became associated with humanist and anti-psychiatry approaches, particularly in regard to understanding schizophrenia and the role of the family. Personality disorders have also been a focus, particularly borderline personality disorder, with the role of dissociation and 'freezing responses' (more extreme reactions than fight-flight when someone is terrified and traumatised) thought to have a significant role in the aetiology of psychological disturbance. Extreme versions of trauma models have implicated the fetal environment and the trauma of being born, but these are not well-supported in the academic literature and have been associated with recovered memory controversies.

People are traumatised by a wide range of people, not just family members. For example, male victims of sexual abuse report being abused in institutional settings (boarding schools, care homes, sports clubs).

Trauma models thus highlight stressful and traumatic factors in early attachment relations and in the development of mature interpersonal relationships. They are often presented as a counterpoint to psychiatric orthodoxy and inform criticisms of mental health research and practice in that it has become too focused on genetics, neurochemistry and medication.

History

From the 1940s to the 1970s prominent mental health professionals proposed trauma models as a means of understanding schizophrenia, including Harry Stack Sullivan, Frieda Fromm-Reichmann, Theodore Lidz, Gregory Bateson, Silvano Arieti and R.D. Laing. Based on their clinical work they theorised that schizophrenia appears to be induced by children's experiences in profoundly disturbed families and reflect victims attempts to cope with such families and live in societies that are inherently damaging to people's psychological well-being. In the 1950s Sullivan's theory that schizophrenia is related to interpersonal relationships was widely accepted in the United States. Silvano Arieti's book Interpretation of Schizophrenia won the American National Book Award in the field of science in 1975. The book advances a psychological model for understanding all the regressive types of the disorder.

Some of the psychogenic models proposed by these early researchers, such as the "schizophrenogenic mother", came under sustained criticism, from feminists who saw them as 'mother-blaming' and from a psychiatric profession that increasingly moved towards biological determinism. From the 1960s pharmacological treatments became the increasing focus of psychiatry, and by the 1980s the theory that the family dynamics could be implicated in the aetiology of schizophrenia became viewed as unacceptable by many mental health professionals in America and Europe. Before his death in 2001, at 90, Theodore Lidz, one of the main proponents of the "schizophrenogenic" parents theory, expressed regret that current research in biological psychiatry was "barking up the wrong tree". Like Lidz, Laing maintained until his death that the cause of both schizoid personality disorder and schizophrenia was influenced by family relationships. And more recent research bears this out, e.g. child abuse has been shown to have a causal role in depression, PTSD, eating disorders, substance abuse and dissociative disorders, and research reveals that the more severe the abuse the higher the probability that psychiatric symptoms will develop in adult life.

Judith Herman's book Trauma and Recovery has heavily influenced therapeutic approaches. Recovery entails three phases which are best worked through sequentially: First 'establishing safety'; secondly 'a process of remembrance and mourning for what was lost'; thirdly 'reconnecting with community and more broadly, society'.

Critiques

Critics of the model, such as August Piper, argue that the logic that childhood trauma causes insanity has a serious flaw: If the claim was true, the abuse of millions of children over the years should have caused higher prevalence rates of mental disorders than the literature reveals. Other critics, particularly proponents of behaviour family therapy, have seen trauma models as parent blaming, and have emphasised the fact that families are usually the main, and often only, source of support for people diagnosed with severe mental illness. Lucy Johnstone has pointed out that some critics advocate family interventions for adult psychiatric patients whilst at the same time maintaining that childhood experiences are not causal as regards mental illness - as if family members can only have a helpful or damaging impact on their adult children.

In response to Piper's assertion, it has been noted that Arieti stated in Interpretation of Schizophrenia that a trauma is more significant when committed by people to whom young human beings are emotionally bonded, and abuse is often interwoven with other forms of neglect and confusing behaviours from care-givers: 

“

First of all we have to repeat here what we already mentioned..., that conditions of obvious external danger, as in the case of wars, disasters, or other adversities that affect the collectivity, do not produce the type of anxiety that hurts the inner self and do not themselves favor schizophrenia. Even extreme poverty, physical illness, or personal tragedies do not necessarily lead to schizophrenia unless they have psychological ramifications that hurt the sense of self. Even homes broken by death, divorce or desertion may be less destructive than homes where both parents are alive, live together, and always undermine the child's conception of himself.

”

Recent approaches

A 2005 meta-analysis of schizophrenia revealed that the prevalence of physical and sexual abuse in the histories of people diagnosed with psychotic disorders is very high and has been understudied. This literature review revealed prevalence rates of childhood sexual abuse in studies of people diagnosed with schizophrenia ranging from 45% to 65%. An analysis of the American National Comorbidity Study revealed that people who have endured three kinds of abuse (e.g., sexual, physical, bullying) are at an 18-fold higher risk of psychosis, whereas those experiencing five types are 193 times more likely to become psychotic. A 2012 review article supported the hypothesis that current or recent trauma may affect an individual's assessment of the more distant past, changing the experience of the past and resulting in dissociative states. Several reviews of risk factors for common mental disorders have emphasised trauma. Such research has rejuvenated interest in this field, both from clinicians, researchers and service user organisations such as the Hearing Voices movement. 

Psychiatrist Colin Ross calls his model the "trauma model of mental disorders" and emphasises that, unlike biological models, this addresses the literature on comorbidity of trauma with mental disorders. Ross describes the theoretical basis of his trauma model as common sense: "The problem faced by many patients is that they did not grow up in a reasonably healthy, normal family. They grew up in an inconsistent, abusive and traumatic family. The very people to whom the child had to attach for survival were also abuse perpetrators and hurt him or her badly.... The basic conflict, the deepest pain, and the deepest source of symptoms, is the fact that mom and dad's behavior hurts, did not fit together, and did not make sense."

In terms of psychoses, most researchers and clinicians believe that genetics remains a causative risk factor but "genes alone do not cause the illness". Modern views of genetics see genes more like dimmer switches, with environmental factors switching the genes on; the more severe the environmental stress, the more effect genes have.

In the field of criminology, Lonnie Athens developed a theory of how a process of brutalization by parents or peers that usually occurs in childhood results in violent crimes in adulthood. Richard Rhodes's Why They Kill describes Athens's observations about domestic and societal violence in the criminals' backgrounds. Both Athens and Rhodes reject the genetic inheritance theories.

Criminologists Jonathan Pincus and Dorothy Otnow Lewis believe that although it is the interaction of childhood abuse and neurological disturbances that explains murder, virtually all of the 150 murderers they studied over a 25-year period had suffered severe abuse as children. Pincus believes that the only feasible remedy for crime would be the prevention of child abuse.

The logical conclusion of the trauma model is that the task for clinicians is not to treat biological disorders but to help people manage and modify their learned, and often embedded, responses to traumas they have experienced. As such, services need to be reconstituted to focus on this aim.

Criticism of evolutionary psychology

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Evolutionary psychology has generated substantial controversy and criticism. The criticism includes but is not limited to: disputes about the testability of evolutionary hypotheses, alternatives to some of the cognitive assumptions (such as massive modularity) frequently employed in evolutionary psychology, alleged vagueness stemming from evolutionary assumptions (such as uncertainty about the environment of evolutionary adaptation), differing stress on the importance of non-genetic and non-adaptive explanations, and political and ethical issues.

While evolutionary psychology has been accused of straw man evidence, ideologically rather than scientifically motivated, evolutionary psychologists respond by arguing that these criticisms are also straw men, are based on an incorrect nature versus nurture dichotomy, or are based on misunderstandings of the discipline.

History

The history of the debate from the critics' perspective is detailed by Gannon (2002). Critics of evolutionary psychology include the philosophers of science David Buller author of Adapting Minds, Robert C. Richardson author of Evolutionary Psychology as Maladapted Psychology, and Brendan Wallace, author of Getting Darwin Wrong: Why Evolutionary Psychology Won't Work. Other critics include neurobiologists like Steven Rose who edited "Alas, Poor Darwin: Arguments against Evolutionary Psychology", and biological anthropologists like Jonathan Marks and social anthropologists like Tim Ingold and Marshall Sahlins.

The evolutionary psychology response to critics has been covered in books by Segerstråle (2000), Defenders of the Truth: The Battle for Science in the Sociobiology Debate and Beyond, Barkow (2005), Missing the Revolution: Darwinism for Social Scientists, and Alcock (2001), The Triumph of Sociobiology.

Massive modularity

Evolutionary psychologists have postulated that the mind is composed of cognitive modules specialized to perform specific tasks. Evolutionary psychologists have theorized that these specialized modules enabled our ancestors to react quickly and effectively to environmental challenges. As a result, domain-specific modules would have been selected for, whereas broad general-purpose cognitive mechanisms that worked more slowly would have been eliminated in the course of evolution.

A number of cognitive scientists have criticized the modularity hypothesis, citing neurological evidence of brain plasticity and changes in neural networks in response to environmental stimuli and personal experiences. Steven Quartz and Terry Sejnowski, for example, have argued that the view of the brain as a collection of specialized circuits, each chosen by natural selection and built according to a "genetic blueprint", is contradicted by evidence that cortical development is flexible and that areas of the brain can take on different functions. Neurobiological research does not support the assumption by evolutionary psychologists that higher-level systems in the neocortex responsible for complex functions are massively modular. Peters (2013) cites neurological research showing that higher-order neocortical areas can become functionally specialized by way of synaptic plasticity and the experience-dependent changes that take place at the synapse during learning and memory. As a result of experience and learning processes the developed brain can look modular although it is not necessarily innately modular. However, Klasios (2014) responds to Peters' critique.

Another criticism is that there is little empirical support in favor of the domain-specific theory. Leading evolutionary psychologists Leda Cosmides and John Tooby have found that performance on the selection task is content-dependent: People find it easier to detect violations of "if-then” rules when the rules can be interpreted as cheating on a social contract. From this Cosmides and Tooby and other evolutionary psychologists concluded that the mind consisted of domain-specific, context-sensitive modules (including a cheater-detection module). Critics have suggested that Cosmides and Tooby use untested evolutionary assumptions to eliminate rival reasoning theories and that their conclusions contain inferential errors. Davies et al., for example, have argued that Cosmides and Tooby did not succeed in eliminating the general-purpose theory because the adapted Wason selection task they used tested only one specific aspect of deductive reasoning and failed to examine other general-purpose reasoning mechanisms (e.g., reasoning based on syllogistic logic, predicate logic, modal logic, and inductive logic etc.). Furthermore, Cosmides and Tooby use rules that incorrectly represent genuine social exchange situations. Specifically, they posit that someone who received a benefit and does not pay the cost is cheating. However, in real-life social exchange situations people can benefit and not pay without cheating (as in the case of receiving gifts or benefiting from charity).

Some critics have suggested that our genes cannot hold the information to encode the brain and all its assumed modules. Humans share a significant portion of their genome with other species and have corresponding DNA sequences so that the remaining genes must contain instructions for building specialized circuits that are absent in other mammals.

One controversy concerns the particular modularity of mind theory used in evolutionary psychology (massive modularity). Critics argue in favor of other theories.

Fear and phobias as innate or learned

Critics have questioned the proposed innateness of certain phobias, such as fear of snakes. Recent evidence, however, suggests that Japanese macaques, and presumably other primates, have a snake-detection brain module—neurons in the preferential medial and dorsolateral pulvinar—that respond very rapidly to images of snakes, even without any prior exposure to snakes.

Environment of evolutionary adaptedness

One method employed by evolutionary psychologists is using knowledge of the environment of evolutionary adaptedness (EEA) to generate hypotheses regarding possible psychological adaptations.

Part of the critique of the scientific basis of evolutionary psychology is of the concept of the environment of evolutionary adaptation. Evolutionary psychology often assumes that human evolution occurred in a uniform environment, and critics suggest that we know so little about the environment (or probably multiple environments) in which homo sapiens evolved, that explaining specific traits as an adaption to that environment becomes highly speculative.

The evolutionary psychologists John Tooby and Leda Cosmides state that research is confined to certainties about the past, such as pregnancies only occurring in women, and that humans lived in groups. They argue that there are many environmental features that are known regarding our species' evolutionary history. They argue that our hunter-gatherer ancestors dealt with predators and prey, food acquisition and sharing, mate choice, child rearing, interpersonal aggression, interpersonal assistance, diseases and a host of other fairly predictable challenges that constituted significant selection pressures. Knowledge also include things such as nomadic, kin-based lifestyle in small groups, long life for mammals, low fertility for mammals, long female pregnancy and lactation, cooperative hunting and aggression, tool use, and sexual division of labor. Tooby and Cosmides thus argue that enough can be known about the EEA to make hypotheses and predictions.

Empirical evidence

Some hypotheses that certain psychological traits are evolved adaptations have not been empirically corroborated.

Rape and attraction to aggression

Smith et al. (2001) criticized Thornhill and Palmer's hypothesis that a predisposition to rape in certain circumstances might be an evolved sexually dimorphic psychological adaptation. They developed a fitness cost/benefit mathematical model and populated it with estimates of certain parameters (some parameter estimates were based on studies of the Aché in Paraguay). Their model suggested that, on average, the costs of rape for a typical 25-year-old male outweigh benefits by a factor of ten to one. On the basis of their model and parameter estimates, they suggested that this would make it unlikely that rape generally would have net fitness benefits for most men. They also find that rape from raiding other tribes has lower costs but does not offer net fitness benefits, making it also unlikely that was an adaptation.

Beckerman et al. (2009) disputed explanations of male aggression as a reproductive strategy. In a study of the Waorani tribes, the most aggressive warriors had the fewest descendants.

Waist-to-hip ratios

Others have criticized the assertion that men universally preferred women with a waist-to-hip ratio of 0.7 or the "hourglass" figure. Studies of peoples in Peru and Tanzania found that men preferred ratios of 0.9. Cashdan (2008) found that in male preferences for waist-to-hip ratios varied and were correlated to economic dependence for women; societies with less economic equality such as Greece, Japan and Portugal favored lower ratios while more egalitarian societies favored higher hip ratios.

Recent studies utilizing stimuli that match what is found in the local culture, by contrast, show that men display a cross-cultural consensus in preferring a low waist-to-hip ratio (i.e., hourglass-like figure), with some fluctuation depending on whether the local ecology is nutritionally-stressed. Congenitally-blind men also display a preference for hourglass figures in women.

Testability

A frequent criticism of evolutionary psychology is that its hypotheses are difficult or impossible to test, challenging its status as an empirical science. As an example, critics point out that many current traits likely evolved to serve different functions from those they do now, confounding attempts to make backward inferences into history. Evolutionary psychologists acknowledge the difficulty of testing their hypotheses but assert it is nevertheless possible.

Critics argue that many hypotheses put forward to explain the adaptive nature of human behavioural traits are "just-so stories"; neat adaptive explanations for the evolution of given traits that do not rest on any evidence beyond their own internal logic. They allege that evolutionary psychology can predict many, or even all, behaviours for a given situation, including contradictory ones. Therefore, many human behaviours will always fit some hypotheses. Noam Chomsky argued:

"You find that people cooperate, you say, 'Yeah, that contributes to their genes' perpetuating.' You find that they fight, you say, ‘Sure, that’s obvious, because it means that their genes perpetuate and not somebody else's. In fact, just about anything you find, you can make up some story for it."

Leda Cosmides argued in an interview:

"Those who have a professional knowledge of evolutionary biology know that it is not possible to cook up after the fact explanations of just any trait. There are important constraints on evolutionary explanation. More to the point, every decent evolutionary explanation has testable predictions about the design of the trait. For example, the hypothesis that pregnancy sickness is a byproduct of prenatal hormones predicts different patterns of food aversions than the hypothesis that it is an adaptation that evolved to protect the fetus from pathogens and plant toxins in food at the point in embryogenesis when the fetus is most vulnerable – during the first trimester. Evolutionary hypotheses – whether generated to discover a new trait or to explain one that is already known – carry predictions about the nature of that trait. The alternative – having no hypothesis about adaptive function – carries no predictions whatsoever. So which is the more constrained and sober scientific approach?"

A 2010 review article by evolutionary psychologists describes how an evolutionary theory may be empirically tested. A hypothesis is made about the evolutionary cause of a psychological phenomenon or phenomena. Then the researcher makes predictions that can be tested. This involves predicting that the evolutionary cause will have caused other effects than the ones already discovered and known. Then these predictions are tested. The authors argue numerous evolutionary theories have been tested in this way and confirmed or falsified. Buller (2005) makes the point that the entire field of evolutionary psychology is never confirmed or falsified; only specific hypotheses, motivated by the general assumptions of evolutionary psychology, are testable. Accordingly, he views evolutionary psychology as a paradigm rather than a theory, and attributes this view to prominent evolutionary psychologists including Cosmides, Tooby, Buss, and Pinker.

In his review article "Discovery and Confirmation in Evolutionary Psychology" (in The Oxford Handbook of Philosophy of Psychology) Edouard Machery concludes:

"Evolutionary psychology remains a very controversial approach in psychology, maybe because skeptics sometimes have little first-hand knowledge of this field, maybe because the research done by evolutionary psychologists is of uneven quality. However, there is little reason to endorse a principled skepticism toward evolutionary psychology: Although clearly fallible, the discovery heuristics and the strategies of confirmation used by evolutionary psychologists are on a firm grounding."

Steve Stewart-Williams argues, in response to claims that evolutionary psychology hypotheses are unfalsifiable, that such claims are logically incoherent. Stewart-Williams argues that if evolutionary psychology hypotheses can't be falsified, then neither could competing explanations, because if alternative explanations (e.g sociocultural hypotheses) were proven true, this would automatically falsify the competing evolutionary psychology hypothesis, so for competing explanations to be true, then evolutionary psychology hypothesis must be false and thus falsifiable.

Ethnocentrism

One aspect of evolutionary psychology is finding traits that have been shown to be universal in humans. Many critics have pointed out that many traits considered universal at some stage or another by evolutionary psychologists often turn out to be dependent on cultural and particular historical circumstances. Critics allege that evolutionary psychologists tend to assume that their own current cultural context represents a universal human nature. For example, anthropologist Susan McKinnon argues that evolutionary theories of kinship rest on ethnocentric presuppositions. Evolutionary psychologists assert that the degree of genetic relatedness determines the extent of kinship (e.g., solidarity, nurturance, and altruism) because in order to maximize their own reproductive success, people "invest" only in their own genetic children or closely related kin. Steven Pinker, for instance, stated "You're either someone's mother or you aren't". McKinnon argues that such biologically centered constructions of relatedness result from a specific cultural context: the kinship category "mother" is relatively self-evident in Anglo-American cultures where biology is privileged but not in other societies where rank and marital status, not biology, determine who counts as a mother or where mother's sisters are also considered mothers and one's mother's brother is understood as the "male mother".

In a review of Pinker's book on evolutionary psychology (The Blank Slate), Louis Menand wrote: "In general, the views that Pinker derives from 'the new sciences of human nature' are mainstream Clinton-era views: incarceration is regrettable but necessary; sexism is unacceptable, but men and women will always have different attitudes toward sex; dialogue is preferable to threats of force in defusing ethnic and nationalist conflicts; most group stereotypes are roughly correct, but we should never judge an individual by group stereotypes; rectitude is all very well, but 'noble guys tend to finish last'; and so on."

However, evolutionary psychologists point out that their research actually focuses on commonalities between people of different cultures to help to identify "human psychological nature" and cultural universals. It is not a focus on local behavioral variation (which may sometimes be considered ethnocentric) that interests evolutionary psychologists; rather their focus is to find underlying psychological commonalities between people from various cultures.

Reductionism and determinism

Some critics view evolutionary psychology as influenced by genetic determinism and reductionism.

Evolutionary psychology is based on the theory that human physiology and psychology are influenced by genes. Evolutionary psychologists assume that genes contain instructions for building and operating an organism and that these instructions are passed from one generation to the next via genes.

Lickliter and Honeycutt (2003) have argued that evolutionary psychology is a predeterministic and preformationistic approach that assumes that physical and psychological traits are predetermined and programmed while virtually ignoring non-genetic factors involved in human development. Even when evolutionary psychologists acknowledge the influence of the environment, they reduce its role to that of an activator or trigger of the predetermined developmental instructions presumed to be encoded in a person's genes. Lickliter and Honeycutt have stated that the assumption of genetic determinism is most evident in the theory that learning and reasoning are governed by innate, domain-specific modules. Evolutionary psychologists assume that modules preexist individual development and lie dormant in the structure of the organism, awaiting activation by some (usually unspecified) experiential events. Lickliter and Honeycutt have opposed this view and suggested that it is the entire developmental system, including the specific features of the environment a person actually encounters and interacts with (and not the environments of distant ancestors) that brings about any modularity of cognitive function.

 

Critics argue that a reductionist analysis of the relationship between genes and behavior results in a flawed research program and a restricted interpretation of the evidence, creating problems for the creation of models attempting to explain behavior. Lewontin, Rose & Kamin instead advocate a dialectical interpretation of behavior in which "it is not just that wholes are more than the sum of their parts, it is that parts become qualitatively new by being parts of the whole". They argue that reductionist explanations such as the hierarchical reductionism proposed by Richard Dawkins will cause the researcher to miss dialectical ones. Similarly, Hilary Rose criticizes evolutionary psychologists' explanations of child abuse as excessively reductionist. As an example she cites Martin Daly and Margot Wilson's theory that stepfathers are more abusive because they lack the nurturing instinct of natural parents and can increase their reproductive success in this way. According to Rose this does not explain why most stepfathers do not abuse their children and why some biological fathers do. She also argues that cultural pressures can override the genetic predisposition to nurture as in the case of sex-selective infanticide prevalent in some cultures where male offspring are favored over female offspring.

Evolutionary psychologists Workman and Reader reply that while reductionism may be a "dirty word" to some it is actually an important scientific principle. They argue it is at the root of discoveries such as the world being made up of atoms and complex life being the result of evolution. At the same time they emphasize that it is important to look at all "levels" of explanations, e.g. both psychologists looking at environmental causes of depression and neuroscientists looking the brain contribute to different aspects of our knowledge of depression. Workman and Reader also deny the accusation of genetic determinism, asserting that genes usually do not cause behaviors absolutely but predispose to certain behaviors that are affected by factors such as culture and an individual's life history.

Alternative explanations

Adaptive explanations vs. environmental, cultural, social, and dialectical explanations

A common critique is that evolutionary psychology does not address the complexity of individual development and experience and fails to explain the influence of genes on behavior in individual cases.

Critics assert that evolutionary psychology has trouble developing research that can distinguish between environmental and cultural explanation and adaptive evolutionary explanations. Some studies have been criticized for their tendency to attribute to evolutionary processes elements of human cognition that may be attributable to social processes (e.g. preference for particular physical features in mates), cultural artifacts (e.g. patriarchy and the roles of women in society), or dialectical considerations (e.g. behaviours in which biology interacts with society, as when a biologically determined skin colour determines how one is treated). Evolutionary psychologists are frequently criticized for ignoring the vast bodies of literature in psychology, philosophy, politics and social studies. Both sides of the debate stress that statements such as "biology vs. environment" and "genes vs. culture" amount to false dichotomies, and outspoken critics of sociobiology such as Richard Lewontin, Steven Rose and Leon Kamin helped to popularise a "dialectical" approach to questions of human behaviour, where biology and environment interact in complex ways to produce what we see.

Evolutionary psychologists respond that their discipline is not primarily concerned with explaining the behavior of specific individuals, but rather broad categories of human behaviors across societies and cultures. It is the search for species-wide psychological adaptations (or "human nature") that distinguishes evolutionary psychology from purely cultural or social explanations. These psychological adaptations include cognitive decision rules that respond to different environmental, cultural, and social circumstances in ways that are (on average) adaptive.

Evolutionary psychologists Confer et al. argue that evolutionary psychology fully accepts nature-nurture interactionism, and that it is possible to test the theories in order to distinguish between different explanations.

Adaptive explanations vs. other evolutionary mechanisms

Critics point out that within evolutionary biology there are many other non-adaptive pathways along which evolution can move to produce the behaviors seen in humans today. Natural selection is not the only evolutionary process that can change gene frequencies and produce novel traits. Genetic drift is caused by chance variation in the genes, environment, or development. Evolutionary by-products are traits that were not specially designed for an adaptive function, although they may also be species-typical and may also confer benefits on the organism. A "spandrel" is a term coined by Gould and Lewontin (1979a) for traits which confer no adaptive advantage to an organism, but are 'carried along' by an adaptive trait. Gould advocates the hypothesis that cognition in humans came about as a spandrel: "Natural selection made the human brain big, but most of our mental properties and potentials may be spandrels – that is, nonadaptive side consequences of building a device with such structural complexity". Once a trait acquired by some other mechanism confers an adaptive advantage, it may be open to further selection as an "exaptation". Evolutionary psychologists suggest that critics misrepresent their field, and that their empirical research is designed to help identify which psychological traits are prone to adaptations, and which are not.

Edward Hagen argued evolutionary psychology's reliance on adaptive explanations is grounded in the fact that the existence and survival of life is highly improbable. Hagen argues that most organisms do not survive to reproduce and that is only through adaptations that organisms can hope to do so; alternate explanations like genetic drift are only relevant if an organism can survive and reproduce in the first place and it is the fact that organisms do manage survive and reproduce, despite the odds against such a thing occurring, that evolutionary psychologists are interested in. Hagen also argues that a way to distinguish spandrels from adaptations is that adaptations have evidence of design (that is to say they did not simply arise by pure chance but were selected for). While Hagen agrees that one can risk over-attributing adaptation, he observes that one can also risk under-attributing it as well. Hagen argues that tonsils can become infected and it needs to be known whether or not it is safe to remove them. Insisting that tonsils could just be spandrels is not helpful, whereas hypothesising that they may be adapations allows one to make predictions about them to see if they do have a function and thus whether or not it is safe to remove them. Conversely, Steve Stewart-Williams argues that it is not true that evolutionary psychologists do not consider non-adaptive explanations, arguing that evolutionary psychologists have suggested alternate explanations such as byproducts, observing that the hypothesis that obesity is caused by a mismatch between ancestral and modern environments is one of the most famous cases of a byproduct explanation in evolutionary psychology.

Durrant et al agree that alternative explanations to adaptation have to be considered. The authors argue that an issue with adaptationist explanations is underdetermination. A theory is underdetermined when the evidence used to support it could be equally used to support one or more other competing theories. Underdetermination is an issue in science due to the problem of induction; in the great majority of cases, the truth of the data does not deductively entail the truth of the hypothesis. While this is an issue in general in science, sciences which deal with unobserved entities and processes, which evolutionary psychology does, are particularly vulnerable. Even if the theory can make predictions, these predictions do not necessarily confirm the hypothesis, as competing theory could also predict it; the authors argue that the prediction of novel facts does not necessarily mean acceptance of the theory, historically speaking, observing that while Einstein's theory of general relativity is famously held as being accepted because it predicted light would bend around black holes (which was unknown at the time), neither Einstein nor many of his contemporaries regarded it as a strong confirmation of his theory. Durrant et al thus propose that the problem of underdetermination can be solved by judging competing theories on a range of criteria to determine which one best explains phenomena by having the best explanatory coherence; criteria suggested include explanatory breadth (which theory explains the great range of facts), simplicity (which theory requires the fewest special assumptions) and analogy (the theory is supported by analogy to theories scientists already find credible). Thus any criticism of adaptationist theories must demonstrate that an alternative theory offers greater explanatory coherence than the adaptationist one.

Disjunction and grain problems

Some have argued that even if the theoretical assumptions of evolutionary psychology turned out to be true, it would nonetheless lead to methodological problems that would compromise its practice. The disjunction and grain problems are argued to create methodological challenges related to the indeterminacy of evolutionary psychology’s adaptive functions. That is, the inability to correctly choose, from a number of possible answers to the question: "what is the function of a given mechanism?"

The disjunction problem occurs when a mechanism appears to respond to one thing (F), but is also correlated with another (G). Whenever F is present, G is also present, and the mechanism seems to respond to both F and G. The difficulty thus involves deciding whether to characterize the mechanism's adaptive function as being related to F, G, or both. "For example, a frogs pre-catching mechanism responds to flies, bees, food pellets, etc.; so is its adaptation attuned to flies, bees, fleebees, pellets, all of these, or just some?"

The grain problem refers to the challenge in knowing what kind of environmental 'problem' an adaptive mental mechanism might have solved. As summarized by Sterenly & Griffiths (1999): "What are the problems 'out there' in the environment? Is the problem of mate choice a single problem or a mosaic of many distinct problems? These problems might include: When should I be unfaithful to my usual partner? When should I desert my old partner? When should I help my sibs find a partner? When and how should I punish infidelity?" The grain problem therefore refers to the possibility that an adaptive problem may actually involve a set of nested 'sub-problems' "which may themselves relate to different input domains or situations. Franks states that "if both adaptive problems and adaptive solutions are indeterminate, what chance is there for evolutionary psychology?"

Franks also states that "The arguments in no sense count against a general evolutionary explanation of psychology." and that by relaxing assumptions the problems may be avoided, although this may reduce the ability to make detailed models.

Behaviors that reduce reproductive success

"Maladaptive" behaviors such as homosexuality and suicide seem to reduce reproductive success and pose a challenge for evolutionary psychology. Evolutionary psychologists have proposed explanations, such that there may be higher fertility rates for the female relatives of homosexual men, thus progressing a potential homosexual gene, or that they may be byproducts of adaptive behaviors that usually increase reproductive success. However, a review by Confer et al. states that they "remain at least somewhat inexplicable on the basis of current evolutionary psychological accounts". If seen to be of a maladaptive nature, and therefore disregarding the evolutionary psychological evidence for things such as homosexuality, these behaviours can simply be seen in a no different manner than other maladaptations such as poor eyesight.

Ethical implications

Many critics have argued that evolutionary psychology and sociobiology justify existing social hierarchies and reactionary policies. Evolutionary psychologists have been accused of conflating "is" and "ought", and evolutionary psychology has been used to argue against social change (because the way things are now has been evolved and adapted) and against social justice (e.g. the argument that the rich are only rich because they've inherited greater abilities, so programs to raise the standards of the poor are doomed to fail).

It has also been suggested by critics that evolutionary psychologists' theories and interpretations of empirical data rely heavily on ideological assumptions about race and gender. Halford Fairchild, for example, argues that J. Philippe Rushton's work on race and intelligence was influenced by preconceived notions about race and was "cloaked in the nomenclature, language and 'objectivity'" of evolutionary psychology, sociobiology and population genetics.

Moreover, evolutionary psychology has been criticized for its ethical implications. Richardon (2007) and Wilson et al. (2003) have cited the theories in A Natural History of Rape where rape is described as a form of mate choice that enhances male fitness as examples. Critics have expressed concern over the moral consequences of such evolutionary theories and some critics have understood them to justify rape. However, empirical research has found that, compared to a control group, exposure to evolutionary psychology theories had no observable impact on male judgments of men’s criminal sexual behavior.

Evolutionary psychologists caution against committing the naturalistic fallacy – the idea that "ought can be derived from is" and that "what is natural" is necessarily a moral good. In the book The Blank Slate, Steven Pinker contends that critics have committed two logical fallacies:

The naturalistic fallacy is the idea that what is found in nature is good. It was the basis for Social Darwinism, the belief that helping the poor and sick would get in the way of evolution, which depends on the survival of the fittest. Today, biologists denounce the Naturalistic Fallacy because they want to describe the natural world honestly, without people deriving morals about how we ought to behave -- as in: If birds and beasts engage in adultery, infanticide, cannibalism, it must be OK. The moralistic fallacy is that what is good is found in nature. It lies behind the bad science in nature-documentary voiceovers: lions are mercy-killers of the weak and sick, mice feel no pain when cats eat them, dung beetles recycle dung to benefit the ecosystem and so on. It also lies behind the romantic belief that humans cannot harbor desires to kill, rape, lie, or steal because that would be too depressing or reactionary.

Similarly, the authors of A Natural History of Rape, Thornhill and Palmer, as well as McKibbin et al. respond to allegations that evolutionary psychologists legitimizes rape by arguing that their critics' reasoning is a naturalistic fallacy in the same way it would be a fallacy to accuse the scientists doing research on the causes of cancer of justifying cancer. Instead, they argue that understanding the causes of rape may help create preventive measures.

Wilson et al. (2003) have stated that evolutionary psychologists are themselves confused about the naturalistic fallacy and misuse it to forestall legitimate ethical discussions. The authors have argued that a factual statement must be combined with an ethical statement to derive an ethical conclusion. Thus, "ought" cannot be described exclusively from "is". They have suggested that if one combines Thornhill and Palmer's theory that rape increases the fitness of a woman's offspring with the ethical premise that it is right to increase fitness of offspring, the resulting deductively valid conclusion is that rape has also positive effects and that its ethical status is ambiguous. Wilson et al. have stated: "Any critic who objects to Thornhill and Palmer's evolutionary interpretation of rape on ethical grounds is dismissed with the phrase 'naturalistic fallacy' like a child stupid enough to write 2+2=5, stifling any meaningful discussion of the ethical issues surrounding the subject of rape. Yet, it is Thornhill and Palmer who are thinking fallaciously by using the naturalistic fallacy in this way." However, in the same article these authors also note that "...we want to stress that we are sympathetic with the goals of evolutionary psychology and think that research should proceed on all fronts, including the possibility that unethical behaviors such as rape evolved by natural selection".

Political stance

Part of the controversy has consisted in each side accusing the other of holding or supporting extreme political viewpoints: evolutionary psychology has often been accused of supporting right-wing politics, whereas critics have been accused of being motivated by Marxist view points.

Linguist and activist Noam Chomsky has said that evolutionary psychologists often ignore evidence that might harm the political status quo:

The founder of what is now called "sociobiology" or "evolutionary psychology"-the natural historian and anarchist Peter Kropotkin-concluded from his investigations of animals and human life and society that "mutual aid" was a primary factor in evolution, which tended naturally toward communist anarchism....Of course, Kropotkin is not considered the founding figure of the field and is usually dismissed if mentioned at all, because his quasi-Darwinian speculations led to unwanted conclusions.

Chomsky has also said that not enough is known about human nature to point to any political conclusions.

Evolutionary psychologist Glenn Wilson argues that "promoting recognition of the true power and role of instincts is not the same as advocating the total abandonment of social restraint". Left-wing philosopher Peter Singer in his book A Darwinian Left has argued that the view of human nature provided by evolution is compatible with and should be incorporated into the ideological framework of the Left.

Evolutionary psychology critics have argued that researchers use their research to promote a right-wing agenda. Evolutionary psychologists conducted a 2007 study investigating the views of a sample of 168 United States PhD psychology students. The authors concluded that those who self-identified as adaptationists were much less conservative than the general population average. They also found no differences compared to non-adaptationist students and found non-adaptationists to express a preference for less strict and quantitative scientific methodology than adaptationists. A 2012 study found that evolutionary anthropology students were largely of a left-liberal political stance and differed little in political opinions from those of other psychology students.

Inclusive fitness

From Wikipedia, the free encyclopedia

In evolutionary biology, inclusive fitness is one of two metrics of evolutionary success as defined by W. D. Hamilton in 1964:

• Personal fitness is the number of offspring that an individual begets (regardless of who rescues/rears/supports them)
• Inclusive fitness is the number of offspring equivalents that an individual rears, rescues or otherwise supports through its behaviour (regardless of who begets them)

An individual's own child, who carries one half of the individual's genes, is defined as one offspring equivalent. A sibling's child, who will carry one-quarter of the individual's genes, is 1/2 offspring equivalent. Similarly, a cousin's child, who has 1/16 of the individual's genes, is 1/8 offspring equivalent.

From the gene's point of view, evolutionary success ultimately depends on leaving behind the maximum number of copies of itself in the population. Prior to Hamilton's work, it was generally assumed that genes only achieved this through the number of viable offspring produced by the individual organism they occupied. However, this overlooked a wider consideration of a gene's success, most clearly in the case of the social insects where the vast majority of individuals do not produce (their own) offspring.

Overview

Hamilton showed mathematically that, because other members of a population may share one's genes, a gene can also increase its evolutionary success by indirectly promoting the reproduction and survival of other individuals who also carry that gene. This is variously called "kin theory", "kin selection theory" or "inclusive fitness theory". The most obvious category of such individuals is close genetic relatives, and where these are concerned, the application of inclusive fitness theory is often more straightforwardly treated via the narrower kin selection theory. 

Hamilton's theory, alongside reciprocal altruism, is considered one of the two primary mechanisms for the evolution of social behaviors in natural species and a major contribution to the field of sociobiology, which holds that some behaviors can be dictated by genes, and therefore can be passed to future generations and may be selected for as the organism evolves. 

Although described in seemingly anthropomorphic terms, these ideas apply to all living things, and can describe the evolution of innate and learned behaviors over a wide range of species including insects, small mammals or humans.

Belding's ground squirrel provides an example. The ground squirrel gives an alarm call to warn its local group of the presence of a predator. By emitting the alarm, it gives its own location away, putting itself in more danger. In the process, however, the squirrel may protect its relatives within the local group (along with the rest of the group). Therefore, if the effect of the trait influencing the alarm call typically protects the other squirrels in the immediate area, it will lead to the passing on of more copies of the alarm call trait in the next generation than the squirrel could leave by reproducing on its own. In such a case natural selection will increase the trait that influences giving the alarm call, provided that a sufficient fraction of the shared genes include the gene(s) predisposing to the alarm call.

Synalpheus regalis, a eusocial shrimp, also is an example of an organism whose social traits meet the inclusive fitness criterion. The larger defenders protect the young juveniles in the colony from outsiders. By ensuring the young's survival, the genes will continue to be passed on to future generations.

Inclusive fitness is more generalized than strict kin selection, which requires that the shared genes are identical by descent. Inclusive fitness is not limited to cases where "kin" ('close genetic relatives') are involved.

Hamilton's rule

In the context of sociobiology, Hamilton proposed that inclusive fitness offers a mechanism for the evolution of altruism. He claimed that this leads natural selection to favor organisms that behave in ways that correlate with maximizing their inclusive fitness. If a gene (or gene complex) promoting altruistic behavior has copies of itself in others, helping those others survive ensures that the genes will be passed on. 

Hamilton's rule describes mathematically whether or not a gene for altruistic behavior will spread in a population:

${\displaystyle c$

where

• ${\displaystyle r\ }$ is the probability, above the population average, of the individuals sharing an altruistic gene – commonly viewed as "degree of relatedness".
• ${\displaystyle b\ }$ is the reproductive benefit to the recipient of the altruistic behavior, and
• ${\displaystyle c\ }$ is the reproductive cost to the altruist,

Gardner et al. (2007) suggest that Hamilton's rule can be applied to multi-locus models, but that it should be done at the point of interpreting theory, rather than the starting point of enquiry. They suggest that one should "use standard population genetics, game theory, or other methodologies to derive a condition for when the social trait of interest is favored by selection and then use Hamilton's rule as an aid for conceptualizing this result".

Altruism

The concept serves to explain how natural selection can perpetuate altruism. If there is an "altruism gene" (or complex of genes) that influences an organism's behavior to be helpful and protective of relatives and their offspring, this behavior also increases the proportion of the altruism gene in the population, because relatives are likely to share genes with the altruist due to common descent. In formal terms, if such a complex of genes arises, Hamilton's rule (rbc) specifies the selective criteria (in terms of cost, benefit and relatedness) for such a trait to increase in frequency in the population. Hamilton noted that inclusive fitness theory does not by itself predict that a species will necessarily evolve such altruistic behaviors, since an opportunity or context for interaction between individuals is a more primary and necessary requirement in order for any social interaction to occur in the first place. As Hamilton put 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). In other words, whilst inclusive fitness theory specifies a set of necessary criteria for the evolution of altruistic traits, it does not specify a sufficient condition for their evolution in any given species. More primary necessary criteria include the existence of gene complexes for altruistic traits in gene pool, as mentioned above, and especially that "a suitable social object is available", as Hamilton noted. Paul Sherman, who has contributed much research on the ground squirrels mentioned above, gives a fuller discussion of Hamilton's latter point:

To understand any species' pattern of nepotism, two questions about individuals' behavior must be considered: (1) what is reproductively ideal?, and (2) what is socially possible? With his formulation of "inclusive fitness," Hamilton suggested a mathematical way of answering (1). Here I suggest that the answer to (2) depends on demography, particularly its spatial component, dispersal, and its temporal component, mortality. Only when ecological circumstances affecting demography consistently make it socially possible will nepotism be elaborated according to what is reproductively ideal. For example, if dispersing is advantageous and if it usually separates relatives permanently, as in many birds (Nice 1937: 180-187; Gross 1940; Robertson 1969), on the rare occasions when nestmates or other kin live in proximity, they will not preferentially cooperate. Similarly, nepotism will not be elaborated among relatives that have infrequently coexisted in a population's or a species' evolutionary history. If an animal's life history characteristics (Stearns 1976; Warner this volume) usually preclude the existence of certain relatives, that is if kin are usually unavailable, the rare coexistence of such kin will not occasion preferential treatment. For example, if reproductives generally die soon after zygotes are formed, as in many temperate zone insects, the unusual individual that survives to interact with its offspring is not expected to behave parentally. (Sherman 1980, 530, underlining in original)

The occurrence of sibling cannibalism in several species underlines the point that inclusive fitness theory should not be understood to simply predict that genetically related individuals will inevitably recognize and engage in positive social behaviors towards genetic relatives. Only in species that have the appropriate traits in their gene pool, and in which individuals typically interacted with genetic relatives in the natural conditions of their evolutionary history, will social behavior potentially be elaborated, and consideration of the evolutionarily typical demographic composition of grouping contexts of that species is thus a first step in understanding how selection pressures upon inclusive fitness have shaped the forms of its social behavior. Dawkins gives a simplified illustration:

If families [genetic relatives] 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)

Evidence from a variety of species including humans, primates, and other social mammals suggests that contextual cues (such as familiarity) are often significant proximate mechanisms mediating the expression of altruistic behavior, regardless of whether the participants are always in fact genetic relatives or not. This is nevertheless evolutionarily stable since selection pressure acts on the typical conditions, not on the rare occasions where actual genetic relatedness differs from that normally encountered (see Sherman above). Inclusive fitness theory thus does not imply that organisms evolve to direct altruism towards genetic relatives. Many popular treatments do however promote this interpretation, as illustrated in a recent review:

[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)

Such misunderstandings of inclusive fitness' implications for the study of altruism, even amongst professional biologists utilizing the theory, are widespread, prompting prominent theorists to regularly attempt to highlight and clarify the mistakes. Here is one recent example of attempted clarification from West et al. (2010):

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)

Green-beard effects

As well as interactions in reliable contexts of genetic relatedness, altruists may also have some way to recognize altruistic behavior in unrelated individuals and be inclined to support them. As Dawkins points out in The Selfish Gene (Chapter 6) and The Extended Phenotype, this must be distinguished from the green-beard effect. 

The green-beard effect is the act of a gene (or several closely linked gene), that:

1. Produces a phenotype.
2. Allows recognition of that phenotype in others.
3. Causes the individual to preferentially treat other individuals with the same gene.

The green-beard effect was originally a thought experiment by Hamilton in his publications on inclusive fitness in 1964, although it hadn't yet been observed. As of today, it has been observed in few species. Its rarity is probably due to its susceptibility to 'cheating' whereby individuals can gain the trait that confers the advantage, without the altruistic behavior. This normally would occur via the crossing over of chromosomes which happens frequently, often rendering the green-beard effect a transient state. However, Wang et al. has shown in one of the species where the effect is common (fire ants), recombination cannot occur due to a large genetic transversion, essentially forming a supergene. This, along with homozygote inviability at the green-beard loci allows for the extended maintenance of the green-beard effect.

Equally, cheaters may not be able to invade the green-beard population if the mechanism for preferential treatment and the phenotype are intrinsically linked. In budding yeast (Saccharomyces cerevisiae), the dominant allele FLO1 is responsible for flocculation (self-adherence between cells) which helps protect them against harmful substances such as ethanol. While 'cheater' yeast cells occasionally find their way into the biofilm-like substance that is formed from FLO1 expressing yeast, they cannot invade as the FLO1 expressing yeast will not bind to them in return, and thus the phenotype is intrinsically linked to the preference.

Parental care

In The Selfish Gene, Dawkins reported that some question the idea that parental investment (parental care) contributes to inclusive fitness. The distinctions between the kind of beneficiaries nurtured (collateral versus descendant relatives) and the kind of fitnesses used (inclusive versus personal) in the parsing of nature are independent concepts. This orthogonality can best be understood in a thought experiment: Consider a model of a population of animals such as crocodiles or tangle web spiders. Some species or populations of these spiders and reptiles exhibit parental care, while closely related species or populations lack it. Assume that in these animals a gene, called a, codes for parental care, and its other allele, called A, codes for an absence thereof. The aa homozygotes care for their young, and AA homozygotes don't, and the heterozygotes behave like aa homozygotes if a is dominant, and like AA homozygotes if A is dominant, or exhibit some kind of intermediate behavior if there is partial dominance. Other kinds of animals could be considered in which all individuals exhibit parental care, but variation among them would be in the quantity and quality thereof. 

If one considers a life cycle as extending from conception to conception, and an animal is an offspring of parents with poor parental care, then the higher mortality with poor care could be considered a diminution of the offspring's expected fitness. 

Alternatively, if one considers the life cycle as extending from weaning to weaning, the same mortality would be considered a diminution in the parents' fecundity, and therefore a diminution of the parent's fitness. 

In Hamilton's paradigm, fitnesses calculated according to in the weaning-to-weaning perspective are inclusive fitnesses, and fitnesses calculated in the conception-to-conception perspective are personal fitnesses. This distinction is independent of whether the altruism involved in child rearing is toward descendants or toward collateral relatives, as when aunts and uncle rear their nieces and nephews. 

Inclusive fitness theory was developed in order to better understand collateral altruism, but this does not mean that it is limited to collateral altruism. It applies just as well to parental care. Which perspective one chooses does not affect the animals but just one's understanding.

Parent offspring conflict and optimization

Early writings on inclusive fitness theory (including Hamilton 1964) used K in place of B/C. Thus Hamilton's rule was expressed as is the necessary and sufficient condition for selection for altruism. 

Where B is the gain to the beneficiary, C is the cost to the actor and r is the number of its own offspring equivalents the actor expects in one of the offspring of the beneficiary. r is either called the coefficient of relatedness or coefficient of relationship, depending on how it is computed. The method of computing has changed over time, as has the terminology. It is not clear whether or not changes in the terminology followed changes in computation.

Robert L. Trivers (1974) defined "parent-offspring conflict" as any case where 

${\displaystyle 1$

i.e., K is between 1 and 2. The benefit is greater than the cost, but is less than twice the cost. 

In this case, the parent would wish the offspring to behave as if r is 1 between siblings, although it is actually presumed to be 1/2 or closely approximated by 1/2.

In other words, a parent would wish its offspring to give up ten offspring in order to raise 11 nieces and nephews. The offspring, when not manipulated by the parent, would require at least 21 nieces and nephews to justify the sacrifice of 10 of its own offspring.

The parent is trying to maximize its number of grandchildren, while the offspring is trying to maximize the number of its own offspring equivalents (via offspring and nieces and nephews) it produces. If the parent cannot manipulate the offspring and therefore loses in the conflict, the grandparents with the fewest grandchildren seem to be selected for. In other words, if the parent has no influence on the offspring's behavior, grandparents with fewer grandchildren increase in frequency in the population.

By extension, parents with the fewest offspring will also increase in frequency.

This seems to go against Ronald A. Fisher's "Fundamental Theorem of Natural Selection" which states that the change in fitness over the course of a generation equals the variance in fitness at the beginning of the generation. Variance is defined as the square of a quantity— standard deviation — and as a square must always be positive (or zero). That would imply that e fitness could never decrease as time passes. This goes along with the intuitive idea that you can't select for lower fitness.

During parent-offspring conflict the number of stranger equivalents reared per offspring equivalents reared is going down.

It is considerations of this phenomenon that have caused Orlove (1979) and Grafen (2006) to say that nothing is being maximized.

According to Trivers (1974), if Freud had tried to explain intra-family conflict after Hamilton instead of before him, he would have attributed the motivation for the conflict and for the to resource allocation issues rather than sexual jealousy.

Incidentally, when k=1 or k=2, the average number of offspring per parent stays constant as time goes by. When k<1 k="" or="">2 then the average number of offspring per parent increases as time goes by.

The term "gene" can refer to a locus (location) on an organism's DNA—a section that codes for a particular trait. Alternative versions of the code at that location are called "alleles." If there are two alleles at a locus, one of which codes for altruism and the other for selfishness, an individual who has one of each is said to be a heterozygote at that locus. If the heterozygote uses half of its resources raising its own offspring and the other half helping its siblings raise theirs, that condition is called codominance. If there is codominance the "2" in the above argument is exactly 2.

If by contrast the altruism allele is more dominant, then the 2 in the above would be replaced by a number smaller than 2. If the selfishness allele is the more dominant, something greater than 2 would replace the 2. (Orlove 1975)

Criticism

A 2010 paper by Martin Nowak, Corina Tarnita, and E. O. Wilson suggested that standard natural selection theory is superior to inclusive fitness theory, stating that the interactions between cost and benefit cannot be explained only in terms of relatedness. This, Nowak said, makes Hamilton's rule at worst superfluous and at best ad hoc. Gardner in turn was critical of the paper, describing it as "a really terrible article", and along with other co-authors has written a reply, submitted to Nature.

In work prior to Nowak et al. (2010), various authors derived different versions of a formula for ${\displaystyle r}$, all designed to preserve Hamilton's rule. Orlove noted that if a formula for ${\displaystyle r}$ is defined so as to ensure that Hamilton's rule is preserved, then the approach is by definition ad hoc. However, he published an unrelated derivation of the same formula for ${\displaystyle r}$ – a derivation designed to preserve two statements about the rate of selection – which on its own was similarly ad hoc. Orlove argued that the existence of two unrelated derivations of the formula for ${\displaystyle r}$ reduces or eliminates the ad hoc nature of the formula, and of inclusive fitness theory as well. The derivations were demonstrated to be unrelated by corresponding parts of the two identical formulae for ${\displaystyle r}$ being derived from the genotypes of different individuals. The parts that were derived from the genotypes of different individuals were terms to the right of the minus sign in the covariances in the two versions of the formula for ${\displaystyle r}$. By contrast, the terms left of the minus sign in both derivations come from the same source. One study suggest the c/b ratio be considered as a continuum of this behavioral trait rather than discontinuous in nature. From this approach fitness transactions can be better observed because there is more to what is happening to affect an individual's fitness than just losing and gaining (Engles, W.R. 1982).