Prosocial behavior

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Prosocial_behavior

Prosocial behavior, or intent to benefit others, is a social behavior that "benefit[s] other people or society as a whole", "such as helping, sharing, donating, co-operating, and volunteering". Obeying the rules and conforming to socially accepted behaviors (such as stopping at a "Stop" sign or paying for groceries) are also regarded as prosocial behaviors. These actions may be motivated by empathy and by concern about the welfare and rights of others, as well as for egoistic or practical concerns, such as one's social status or reputation, hope for direct or indirect reciprocity, or adherence to one's perceived system of fairness. It may also be motivated by altruism, though the existence of pure altruism is somewhat disputed, and some have argued that this falls into philosophical rather than psychological realm of debate. Evidence suggests that pro sociality is central to the well-being of social groups across a range of scales, including schools. Prosocial behavior in the classroom can have a significant impact on a student's motivation for learning and contributions to the classroom and larger community. In the workplace, prosocial behaviour can have a significant impact on team psychological safety, as well as positive indirect effects on employee's helping behaviors and task performance. Empathy is a strong motive in eliciting prosocial behavior, and has deep evolutionary roots.

Prosocial behavior fosters positive traits that are beneficial for children and society. It helps many beneficial functions by bettering production of any league and its organizational scale. Evolutionary psychologists use theories such as kin-selection theory and inclusive fitness as an explanation for why prosocial behavioral tendencies are passed down generationally, according to the evolutionary fitness displayed by those who engaged in prosocial acts. Encouraging prosocial behavior may also require decreasing or eliminating undesirable social behaviors.

Although the term "prosocial behavior" is often associated with developing desirable traits in children, the literature on the topic has grown since the late 1980s to include adult behaviors as well. The term "prosocial" has grown into a world-wide movement, using evolutionary science to create real-world pro-social changes from working groups to our whole culture.

Origin of the term

According to the psychology researcher Daniel Batson, the term "was created by social scientists as an antonym for antisocial."

Reciprocity vs. altruism in motivation

The purest forms of prosocial behavior are motivated by altruism, an unselfish interest in helping another person. According to Santrock, the circumstances most likely to evoke altruism are empathy for an individual in need, or a close relationship between the benefactor and the recipient. However, many prosocial behaviors that appear altruistic are in fact motivated by the norm of reciprocity, which is the obligation to return a favor with a favor. People feel guilty when they do not reciprocate and they may feel angry when someone else does not reciprocate. Reciprocal altruism suggests that "such helping is driven by a genetic tendency". Thus some professionals argue that altruism may not exist, and is completely motivated by reciprocity. Either reciprocity or altruism may motivate many important prosocial behaviors, including sharing.

Situational and individual factors

Prosocial behavior is mediated by both situational and individual factors.

Situational factors

One of the most common situation factors is the occurrence of the bystander effect. The bystander effect is the phenomenon that an individual's likelihood of helping decreases when passive bystanders are present in a critical situation. For example, when someone drops a stack of papers on a crowded sidewalk, most people are likely to continue passing him/her by. This example can be extended to even more urgent situations, such as a car crash or natural disaster.

The decision model of bystander intervention noted that whether or not an individual gives aid in a situation depends upon their analysis of the situation. An individual will consider whether or not the situation requires their assistance, if the assistance is the responsibility of the individual, and how to help.

This model, proposed by Latane and Darley, describes five things that must occur in order for a person to intervene:

1. Notice the situation
2. Construe it as an emergency.
3. Develop feelings of responsibility.
4. Believe they have skills to succeed.
5. Reach a conscious decision to help.

The number of individuals present in the situation requiring help is also a mediating factor in one's decision to give aid, where the more individuals are present, the less likely it is for one particular individual to give aid due to a reduction in perceived personal responsibility. This is known as diffusion of responsibility, where the responsibility one feels for the person(s) in need is divided by the number of bystanders. Another factor that comes into play is evaluation apprehension, which simply refers to the fear of being judged by other bystanders. Finally, pluralistic ignorance may also lead to someone not intervening. This refers to relying on the reaction of others, before reacting yourself.

Additionally, Piliavin et al. (1981) noted that individuals are likely to maximize their rewards and minimize their costs when determining whether or not to give aid in a situation – that is, that people are rationally self-motivated. Prosocial behavior is more likely to occur if the cost of helping is low (i.e. minimal time, or minimal effort), if helping would actually benefit the individual providing the help in some way, and if the rewards of providing the help are large. If it is in an individual's interest to help, they will most likely do so, especially if the cost of not providing the help is great.

People are also more likely to help those in their social group, or their "in group". With a sense of shared identity with the individual requiring assistance, the altruist is more likely to provide help, on the basis that one allocates more time and energy towards helping behavior within individuals of their own group. The labeling of another individual as a member of one's "in-group" leads to greater feelings of closeness, emotional arousal, and a heightened sense of personal responsibility for the other's welfare, all of which increase the motivation to act prosocially.

Researchers have also found that social exclusion decreases the likelihood of prosocial behavior occurring. In a series of seven experiments conducted by Twenge et al., (2007) researchers manipulated social inclusion or exclusion by telling research participants that other participants had purposefully excluded them, or that they would probably end up alone later in life. They found that this preliminary social exclusion caused prosocial behavior to drop significantly, noting that "Socially excluded people donated less money to a student fund, were unwilling to volunteer for further lab experiments, were less helpful after a mishap, and cooperated less in a mixed-motive game with another student." This effect is thought to be due to the fact that prosocial behavior, again, is motivated by a sense of responsibility in caring for and sharing resources with members of one's own group.

Individual factors

Individuals can be compelled to act prosocially based on learning and socialization during childhood. Operant conditioning and social learning positively reinforces discrete instances of prosocial behaviors. Cognitive capacities like intelligence for example, are almost always related to prosocial likings. Helping skills and a habitual motivation to help others is therefore socialized, and reinforced as children understand why helping skills should be used to help others around them.

Social and individual standards and ideals also motivate individuals to engage in prosocial behavior. Social responsibility norms, and social reciprocity norms reinforce those who act prosocially. As an example, consider the child who is positively reinforced for "sharing" during their early childhood years. When acting prosocially, individuals reinforce and maintain their positive self-images or personal ideals, as well as help to fulfill their own personal needs. The correlation between a helper's state and helping tendencies are greatly restricted to the relationship between whoever takes part in the situation.

Emotional arousal is an additional important motivator for prosocial behavior in general. Batson's (1987) empathy-altruism model examines the emotional and motivational component of prosocial behavior. Feeling empathy towards the individual needing aid increases the likelihood that the aid will be given. This empathy is called "empathetic concern" for the other individual, and is characterized by feelings of tenderness, compassion, and sympathy.

Agreeableness is thought to be the personality trait most associated with inherent prosocial motivation. Prosocial thoughts and feelings may be defined as a sense of responsibility for other individuals, and a higher likelihood of experiencing empathy ("other-oriented empathy") both affectively (emotionally) and cognitively. These prosocial thoughts and feelings correlate with dispositional empathy and dispositional agreeableness.

Other factors

In addition to situational and individualistic factors, there are some categorical characteristics that can impact prosocial behavior. Several studies have indicated a positive relationship between prosocial behavior and religion. In addition, there may be sex differences in prosocial behavior, particularly as youths move into adolescence. Research suggests that while women and men both engage in prosocial behaviors, women tend to engage in more communal and relational prosocial behaviors whereas men tend to engage in more agentic prosocial behaviors. A recent study examining workplace charitable giving looked at the role of both sex and ethnicity. Results showed that women gave significantly more than men, and Caucasians gave significantly more than minority groups. However, the percent of minority individuals in the workplace was positively associated with workplace charitable giving by minorities. Culture, sex, and religion are important factors to consider in understanding prosocial behavior on an individual and group level.

In childhood through early adolescence

Prosocial behavior in childhood often begins with questions of sharing and fairness. From age 12–18 months, children begin to display prosocial behavior in presenting and giving their toys to their parents, without promoting or being reinforced by praise. The development of prosocial behavior continues throughout the second year of life, as children begin to gain a moral understanding of the world. As obedience to societal standards becomes important, children's ability to exhibit prosocial behavior strengthens, with occurrence and diversity of these behaviors increasing with age and cognitive maturity. What is important developmentally is that the child has developed a belief that sharing is an obligatory part of a social relationship and involves a question of right and wrong. So, as children move through childhood, their reasoning changes from being hedonistic and needs-oriented to becoming more concerned with approval and more involved in complex cognitive forms of perspective taking and reciprocity reasoning. Additionally, children's prosocial behavior is typically more centered around interest in friends and concern for approval, whereas adolescents begin to develop reasoning that is more concerned with abstract principles such as guilt and positive affect.

Parents can set examples that children carry into their interactions and communication with peers, but parents are not present during all of their children's peer exchanges. The day-to-day constructions of fairness standards is done by children in collaboration and negotiation with each other. Recent research demonstrates that invoking the self using subtle linguistic cues (e.g. identifying someone as a "helper" versus labeling the action, "helping") fosters the perception that a behavior reflects identity, and increases helping, or prosocial, behaviors in children significantly across tasks.

Another study by Nantel-Vivier et al. used a multi-informant model to investigate the development of prosocial behaviour in both Canadian and Italian adolescents aged 10–15. Their findings have indicated that, in early adolescence, although empathy and moral reasoning continue to advance, the development of prosocial behaviors reaches a plateau. Theories for this change in development suggest that it is the result of more individualized and selective prosocial behaviors. During adolescence, youth begin to focus these behaviors toward their peer groups and/or affiliations.

Consistent with previous analyses, this study also found a tendency toward higher prosocial behaviors in young adolescent girls compared to their male classmates. The earlier maturation in females may be a possible explanation for this disparity. A more recent study that focused on the effects of pubertal timing found that early maturation in adolescents has a positive impact on prosocial behaviors. While their findings apply to both genders, this study found a much more pronounced effect in males. This suggests that earlier onset of puberty has a positive correlation with the development of prosocial behaviors.

In many Indigenous American communities, prosocial behavior is a valued means of learning and child rearing. Such behaviors are seen as contributing in an eagerly collaborative and flexible environment, aimed at teaching consideration, responsibility, and skills with the guidance and support of adults. Culturally valued developmental goals are integrally tied to children's participation in these contexts. It is also helpful for children to learn cultural mores in addition to individual personality development. Children learn functional life skills through real-time observation of adults and interactive participation of these learned skills within their community.

Prosocial development in school

Prosocial behavior can act as a strong motivator in education, for it provides students with a purpose beyond themselves and the classroom. This purpose beyond the self, or self-transcendence, is an innate human need to be a part of something bigger than themselves. When learning in isolation, the way Western academics are traditionally designed, students struggle to make connections to the material and its greater overarching purpose. This disconnection harms student learning, motivation, and attitudes about education.

If teachers make space for prosocial behavior in education and social learning, then they can illustrate that what students are learning will have a direct impact on the world that they live in. This would be considered a mutually constituting relationship, or a relationship in which both individuals and culture develop interdependently. In other words, what students are learning in a classroom could be intimately connected with a purpose towards a greater cause, deepening the learning itself.

Studies by Yeager et al. test the effects of having a self-transcendent purpose for learning, with the results showing that such a purpose for learning led to fewer future college dropouts, increased high school math and science GPAs, and persistence on boring tasks. This self transcendent purpose may not only encourage persistence on boring tasks, but may help to make boring tasks more meaningful and engaging.

A person's ideas and opinions are largely shaped by the world that they grow up in, which in turn determines what sort of change they want to instill in the world. For example: a girl who grew up in poverty becoming a social worker. The environment she grew up in gave her an awareness of the workings of poverty, motivating her to instill change in either the institutions that cause it, or help those affected by poverty.

There aren't many opportunities to make prosocial contributions in school; which makes school feel isolated and irrelevant. By encouraging students to find a self-transcendent purpose in their learning, others enable them to enjoy their learning and make connections to community contributions.

Influence of media programming and video games on children

Studies have shown that different types of media programming may evoke prosocial behaviors in children.

The channels aimed at younger viewers like Nickelodeon and Disney Channel had significantly more acts of altruism than the general-audience demographic channels like A&E and or TNT, according to one large-scale study. This study examined the programming of 18 different channels, including more than 2,000 entertainment shows, during a randomly selected week on television. The study revealed that nearly three quarters (73 percent) of programs contained at least one act of altruism and on average viewers saw around three acts of altruism an hour. Around one-third of those behaviors were explicitly rewarded in the plot, potentially sending the message that these acts of prosocial behavior can come with positive consequences.

Another study on the topic was conducted by University at Buffalo, Iowa State University and University of Minnesota professors. They studied children for two years for the purpose of investigating the role of media exposure on prosocial behavior for young boys and girls. The study concluded that media exposure could possibly predict outcomes related to prosocial behavior.

Other experimental research has suggested that prosocial video games may increase prosocial behavior in players although some of this work has proven difficult to replicate. However other scholars have been critical of this work for tending to falsely dichotomize video games into prosocial/violent categories despite significant overlap as well as methodological flaws in the experimental studies. For instance a study by Ferguson and Garza found that exposure to violent video games was associated with increased prosocial behavior, both on-line as well as volunteering in the real world. The authors speculated this may be due to the prosocial themes common in many violent games, as well as team oriented play in many games.

Legislation

In the United States, in an effort to get stations to air education and prosocial programming for children, the Children's Television Act was adopted in 1990. It states that channels must produce and air programming developed specifically for children as a condition to renew broadcast licenses. After discussions as to what the definition of "specifically designed for children" really means, in 1996 guidelines were passed to correct this ambiguity.

Influence of arts

Arts are increasingly recognized as influential for health behaviors in strengthening social bonds and cohesion and promoting prosocial behavior. Evidence of the impact of different arts is emerging and research is growing on literature, movies and theatre. A recent paper resuming the current evidence argues that performative arts are more prone to elicit empathic concern which is linked with more durable prosocial behavior during stressful situations such as the COVID-19 pandemic outbreak: in particular theatre and virtual reality are seen as promising. An active role of the arts in sustaining prosocial behavior should however integrate an ethical approach to avoid the risk of mass manipulation and intergroup bias.

Influence of observation

People are generally much more likely to act pro-socially in a public setting rather than in a private setting. One explanation for this finding has to do with perceived status, being publicly recognized as a pro-social individual often enhance one's self-image and desirability to be considered for inclusion in social groups. Other research has shown that merely given people the "illusion" that they are being observed (e.g., by hanging up posters of "staring" human eyes) can generate significant changes in pro-social acts such as charitable giving and less littering. Pictures of human eyes trigger an involuntary neural gaze detection mechanism, which primes people to act pro-socially. There are two different forms of prosocial behaviors. Ordinary prosocial behavior requires "situational and sociocultural demands". Extraordinary prosocial behavior doesn't include as much. This indicates that one form is used for a more selfish result while the other is not.

Influence of perception of responsibility and guilt

Guilt has long been regarded as a motivator for prosocial behavior. Extensive data from a 2012 study conducted by de Hooge, demonstrates that when a secondary individual repairs a transgressors' damage caused to victims, the transgressors' guilt feelings, reparative intentions, and prosocial behavior drastically diminish. Thus, reduction of guilt may have more to do with reparative actions broadly, rather than necessarily prosocial behaviors taken on by oneself.

Social media in natural disasters

Social media can also be a catalyst for prosocial behavior. One example occurred during the relief efforts in the wake of the 2011 Tōhoku earthquake and tsunami off the coast of Japan, when users turned to Facebook and Twitter to provide financial and emotional support via their social networks. Direct donations to Japanese relief were possible on The Red Cross fan page on Facebook, and via online discount sites like Groupon and LivingSocial.

Relation to mood and emotion

Mood and prosocial behavior are closely linked. People often experience the "feel good-do good" phenomena, where being in a good mood increases helping behaviors. Being in a good mood helps us to see the "good" in other people, and prolongs our own good mood. For example, mood and work behaviors have frequently been examined in research; studies show that positive mood at work is associated with more positive work-related behaviors (e.g., helping co-workers). Similarly, prosocial behaviors increase positive mood. Several studies have shown the benefits of volunteering and other prosocial behaviors on self-esteem, life satisfaction, and overall mental health. Additionally, negative mood can also impact prosocial behavior. Research has shown that guilt often leads to prosocial behaviors, whereas other negative mood states, such as fear, do not lead to the same prosocial behaviors.

A recent pilot study examined whether an intervention increasing prosocial behavior (kind acts) in young adults with social anxiety would both increase positive affect and decrease social anxiety in participants. Participants randomly assigned to a four-week Kind Acts intervention, where individuals were instructed to engage in three kind acts each day twice a week over the four-week period, showed both higher self-reported positive mood and increased satisfaction with relationships at the end of the intervention. This intervention demonstrates ways in which prosocial behavior may be beneficial in improving mood and mental health.

A meta-analysis from 2020 by Hui et al., which looked at 126 prior studies involving almost 200,000 participants, found that spontaneous instances of prosocial behavior, such as helping an older neighbor carry groceries, had a stronger positive effect on well-being than did more formal instances of prosocial behavior, such as volunteering for a charity at a pre-scheduled time.

Other research suggests that cultivating positive emotions, such as gratitude, may also facilitate prosocial behavior. A study by Bartlett & DeSteno examined the ability of gratitude to shape costly prosocial behavior, demonstrating that gratitude increases efforts to assist a benefactor even when such efforts are costly (i.e., hedonically negative), and that this increase is qualitatively different from efforts given from just general positive affective state. They also show that gratitude can increase assistance provided to strangers, not just close social ties. Awe is another positive emotional state that has been closely linked to inspiring generosity and prosocial behavior. Piff et al. studied this phenomenon through experiments using economic and ethical-decision making games and explain, "When people experience awe they really want to share that experience with other people, suggesting that it has this particularly viral component to it... awe binds people together—by causing people to want to share their positive experiences collectively with one another."

Psychopathy and lack of prosocial behavior

Main article: Psychopathy

In 1941, Hervey Cleckley described psychopathy as a disorder in which individuals often initially appear intelligent, charming, and even kind but are in fact egocentric, grandiose and impulsive. He described individuals who would, on a whim, leave their families to cross the country gambling, drinking and fighting, only to return and act as if nothing was out of the ordinary.

Today, psychopathy is described as a personality disorder that is characterized by decreased anxiety, fear, and social closeness as well as increased impulsivity, manipulativeness, interpersonal dominance and aggression. These traits lead to numerous types of antisocial behavior including high rates of substance abuse, serial short term relationships, and various forms of criminal behavior. One common misconception about psychopathy though is that all psychopaths are serial killers or other vicious criminals. In reality, many researchers do not consider criminal behavior to be a criterion for the disorder although the role of criminality in the disorder is strongly debated. Additionally, psychopathy is being researched as a dimensional construct that is one extreme of normal range personality traits instead of a categorical disorder.

In regards to the lack of prosocial behavior in psychopathy, there are several theories that have been proposed in the literature. One theory suggests that psychopaths engage in less prosocial behavior (and conversely more antisocial behavior) because of a deficit in their ability to recognize fear in others, particularly fearful facial expressions. Because they are unable to recognize that their actions are causing another distress, they continue that behavior in order to obtain some goal that benefits them. A second theory proposes that psychopaths have a sense of "altruistic punishment" where they are willing to punish other individuals even if it means they will be harmed in some way. There has also been an evolutionary theory proposed stating that psychopaths lack of prosocial behavior is an adaptive mating strategy in that it allows them to spread more of their genes while taking less responsibility for their offspring. Finally, there is some evidence that in some situations psychopaths behavior may not be antisocial but instead it may be more utilitarian than other individuals. In a recent study, Bartels & Pizarro (2011) found that when making decisions about traditional moral dilemmas such as the trolley problem, individuals high in psychopathic traits actually make more utilitarian (and therefore more moral in some views) choices. This finding is particularly interesting because it suggests that psychopaths, who are often considered immoral or even evil, may actually make better moral decisions than non-psychopaths. The authors of this study conclude that individuals high in psychopathic traits are less influenced by their emotions and therefore make more "mathematical" decisions and choose the option that leads to the lowest number of deaths.

The theories discussed above are not intended to be a comprehensive list but instead to provide a sense of how psychopaths differ in their approach to social interactions. As with most psychological/social phenomena, it is likely a combination of these factors that leads to psychopaths' lack of prosocial behavior. Further research is needed to determine the causal nature of any one of these individual deficits as well as if there is any way to help these individuals develop more prosocial patterns of behavior.

Helper's high

Psychologists have shown that helping others can produce "feel-good" neurotransmitters such as oxytocin and that, similar to any other pleasurable activity, the act of volunteering, giving and behaving pro-socially can become addictive.

Some work has been done on utilizing this principle through the concept of helper therapy, in which therapeutic benefits are gleaned from assisting others. Community health workers have been found to gain helper benefits that include positive feelings about self, a sense of belonging, valuable work experience, and access to health information and skills through their prosocial vocation, which may buffer against the various stressors inherent in this line of work.

In addition, Helper therapy may also be highly beneficial for distressed adolescents experiencing suicidal thoughts. Studies indicate that when help-seeking youth use online community forums, the help-seekers often begin to provide support for other help seekers, and develop a reciprocal prosocial community battling depression together.

Prosocial dissidence

Stefano Passini and Davide Morselli argue that groups will obey authority so long as its system, basis, and demands are viewed as legitimate. Passini and Morselli distinguish between anti-social disobedience, which they see as destructive, and prosocial disobedience, which they see as constructive. "Disobedience becomes prosocial when it is enacted for the sake of the whole society, including all its different levels and groups. In contrast, anti-social disobedience is enacted mainly in favour of one's own group, in order to attain individual rights." A main difference between anti-social and pro-social dissidence is the way that they relate to authority; anti-social dissidents reject authority and disobey its norms and laws, while pro-social dissidents understand the important roles that societal laws play in maintaining order, but also recognize and address the flaws in authoritative reasoning. Pro-social protests, if viewed in a positive manner, can increase freedoms and equality for the general public, and improve democratic institutions.

Labor market outcomes

Recent scientific research shows that individuals who volunteer have better labor market outcomes in terms of hiring opportunities and wages.

Evolution of eusociality

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Evolution_of_eusociality 

 

Honeybee workers collaborating on a comb have given up their ability to reproduce, an extreme expression of eusocial behavior.

Eusociality evolved repeatedly in different orders of animals, particularly the Hymenoptera (the wasps, bees, and ants). This 'true sociality' in animals, in which sterile individuals work to further the reproductive success of others, is found in termites, ambrosia beetles, gall-dwelling aphids, thrips, marine sponge-dwelling shrimp (Synalpheus regalis), naked mole-rats (Heterocephalus glaber), and the insect order Hymenoptera (which includes bees, wasps, and ants). The fact that eusociality has evolved so often in the Hymenoptera (between 8 and 11 times), but remains rare throughout the rest of the animal kingdom, has made its evolution a topic of debate among evolutionary biologists. Eusocial organisms at first appear to behave in stark contrast with simple interpretations of Darwinian evolution: passing on one's genes to the next generation, or fitness, is a central idea in evolutionary biology.

Current theories propose that the evolution of eusociality occurred either due to kin selection, proposed by W. D. Hamilton, or by the competing theory of multilevel selection as proposed by E.O. Wilson and colleagues. No single trait or model is sufficient to explain the evolution of eusociality, and most likely the pathway to eusociality involved a combination of pre-conditions, ecological factors, and genetic influences.

Overview of eusociality

Main article: Eusociality

Eusociality can be characterized by four main criteria: overlapping generations, cooperative brood care, philopatry, and reproductive altruism. Overlapping generations means that multiple generations live together, and that older offspring may help the parents raise their siblings. Cooperative brood care is when individuals other than the parents assist in raising the offspring through means such as food gathering and protection. Philopatry is when individuals remain living in their birthplace.

The final category, reproductive altruism, is the most divergent from other social orders. Altruism occurs when an individual performs a behavior that benefits a recipient in some way, but at the individual's own expense. Reproductive altruism is one of the most extreme forms of altruism. This is when most members of the group give up their own breeding opportunities in order to participate in the reproductive success of other individuals. The individuals giving up their own reproductive success form a sterile caste of workers within the group. All species that practice reproductive altruism produce one or more queens, the only breeding females, who are larger than the rest. The remainder of the society is composed of a few breeding males, sterile male and female workers, and the young.

Early hypotheses

Charles Darwin considered the evolution of eusociality a major problem for his theory of natural selection. In The Origin of Species, he described the existence of sterile worker castes in the social insects as "the one special difficulty, which at first appeared to me insuperable and actually fatal to my whole theory". In the next paragraph of his book, Darwin describes a solution. If the trait of sterility can be carried by some individuals without expression, and those individuals that do express sterility help reproductive relatives, the sterile trait can persist and evolve.

Darwin was on the right track, except sterility is not a characteristic shared among all eusocial animals. Sterile workers of many eusocial species are not actually physiologically sterile. Male workers can still produce sperm, and female workers sometimes lay eggs, and in some species, become the new queen if the old one dies (observed in Hymenoptera, termites, and shrimp).

This insight led to inclusive fitness and kin selection becoming important theories during the 20th century to help explain eusociality. Inclusive fitness is described as a combination of one's own reproductive success and the reproductive success of others that share similar genes. Animals may increase their inclusive fitness through kin selection. Kin selection is when individuals help close relatives with their reproduction process, seemingly because relatives will propagate some of the individual's own genes. Kin selection follows Hamilton's Rule, which suggests that if the benefit of a behavior to a recipient, taking into account the genetic relatedness of the recipient to the altruist, outweighs the costs of the behavior to the altruist, then it is in the altruist's genetic advantage to perform the altruistic behavior.

Current theories

Haplodiploidy/Kin selection

Main articles: Haplodiploidy and Kin selection

William D. Hamilton proposed that eusociality arose in social Hymenoptera by kin selection because of their interesting genetic sex determination trait of haplodiploidy. Because males are produced by parthenogenesis (they come from unfertilized eggs and thus only have one set of chromosomes), and females are produced from fertilized eggs, sisters from a singly-mated mother share (on average) 75% of their genes, whereas mothers always share only 50% of their genes with their offspring. Thus, sisters will propagate their own genes more by helping their mothers to raise more sisters, than to leave the nest and raise their own daughters.

Though Hamilton's argument appears to work well for Hymenoptera, it excludes diploid eusocial organisms (inter-sibling relatedness ≤ parent-offspring relatedness = 0.5). Even in haplodiploid systems, the average relatedness between sisters falls off rapidly when a queen mates with multiple males (r=0.5 for 2 mates, and even lower for more). Moreover, males share only 25% of their sisters' genes, and, in cases of equal sex ratios, females are related to their siblings on average by 0.5 which is no better than raising their own offspring. However, despite the shortcomings of the haplodiploidy hypothesis, it is still considered to have some importance. For example, many bees have female-biased sex ratios and/or invest less in or kill males. Analysis has shown that in Hymenoptera, the ancestral female was monogamous in each of the eight independent cases where eusociality evolved. This indicates that the high relatedness between sisters favored the evolution of eusociality during the initial stages on several occasions. This helps explain the abundance of eusocial genera within the order Hymenoptera, including three separate origins within halictid bees alone.

Monogamy

The monogamy hypothesis, formulated by Jacobus Boomsma in 2007, is currently the leading hypothesis concerning the initial evolution of eusociality in the Hymenoptera. It uses Hamilton's kin selection approach in a way that applies to both haploid and diploid organisms. If a queen is lifetime-strictly monogamous - in other words, she mates with only one individual during her entire life - her progeny will be equally related to their siblings and to their own offspring (r=0.5 in both cases - this is an average of sisters [0.75] and brothers [0.25]). Thus, natural selection will favor cooperation in any situation where it is more efficient to raise siblings than offspring, and this could start paving a path towards eusociality. This higher efficiency becomes especially pronounced after group living evolves.

In many monogamous animals, an individual's death prompts its partner to look for a new mate, which would affect relatedness and hinder the evolution of eusociality: workers would be much more related to their offspring than their siblings. However, many Hymenoptera have a form of lifetime monogamy in which the queen mates with a single male, who then dies before colony founding. This seems to be the ancestral state in all Hymenopteran lineages that have evolved eusociality. Most termites also have a mating system in which a reproductive female (the queen) commits to a single male for life (the king), and this pattern seems to be ancestral in termites. Lastly, strict monogamy facilitated eusociality in the sponge-dwelling shrimp.

Inbreeding

In species where philopatry predominates, and there are few emigrants to the nest, intense inbreeding can occur, as is the case in eusocial species. Inbreeding can mimic and even surpass the effects of haplodiploidy. Siblings may actually share greater than 75% of their genes. Like in haplodiploidy kin selection, the individuals can propagate their own genes more through the promotion of more siblings, rather than their own offspring. For example, the need for dispersal and aggregation of multiclonal groups may have helped to drive the evolution of eusociality in aphids.

Termites

In termites, two additional hypotheses have been proposed. The first is the Chromosomal Linkage Hypothesis, where much of the termite genome is sex-linked. This makes sisters related somewhat above 50%, and brothers somewhat above 50%, but brother-sister relatedness less than 50%. Termite workers might then bias their cooperative brood care towards their own sex. This hypothesis also mimics the effects of haplodiploidy, but proposes that males would help raise only the queen's male offspring, while females would only care for the queen's female offspring.

The symbiont hypothesis in termites is quite different from the others. With each molt, termites lose the lining of their hindgut and the subsequent bacteria and protozoa that colonize their guts for cellulose digestion. They depend on interactions with other termites for their gut to be recolonized, thus forcing them to become social. This could be a precursor, or pre-condition for why eusociality evolved in termites.

Pre-conditions

Although the symbiont hypothesis serves as a pre-condition for termites to evolve into eusocial societies, scientists have found two crucial pre-conditions for the evolution of eusociality across all species. These include: 1. Altricial offspring (require large amounts of parental care to reach maturity); 2. Low reproductive success rates of solitary pairs that attempt to reproduce. These pre-conditions led to the two lifestyle characteristics that are observed in all eusocial species: nest building and extensive parental care.

Ecological factors

Ecological factors were also probably a precursor to eusociality. For example, the sponge-dwelling shrimp depend upon the sponge's feeding current for food, termites depend upon dead, decaying wood, and naked mole rats depend upon tubers in the ground. Each of these resources has patchy distributions throughout the environments of these animals. This means there is a high cost to dispersing (individual may not find another source before it starves), and these resources must be defended for the group to survive. These requirements make it a necessity to have high social order for the survival of the group.

Genetic influences

Genetic constraints may have influenced the evolution of eusociality. The genome structure of the order Hymenoptera has been found to have the highest recombination rates of any other groups in Animalia. The eusocial genus Apis, the honeybees, have the highest recombination rate in higher eukaryotes. Genes determining worker behavior and division of labor have been found in regions of the Apis genome with the highest rates of recombination and molecular evolution. These mechanisms are likely important to the evolution of eusociality because high recombination rates are associated with the creation of novel genes, upon which natural selection can act. This could have been important in other eusocial genera. Biased gene conversion rates are also higher in eusocial species. This could increase genotypic diversity, which could allow workers to meet the demands of a changing social structure more easily. Another hypothesis is that the lower overall genetic diversity as eusociality levels increase throughout the family Apidaeis due to a decreased exposure to parasites and pathogens.

Mechanisms

Manipulation

Eusociality appears to be maintained through manipulation of the sterile workers by the queen. The mechanisms for this include hormonal control through pheromones, restricting food to young in order to control their size, consumption of any eggs laid by females other than the queen, and behavioral dominance. In naked mole rats, this behavioral dominance occurs in the form of the queen facing the worker head-to-head, and shoving it throughout the tunnels of the naked mole rats' burrow for quite a distance.

Group selection

Main article: Group selection

Nowak, et al. (2010) outlines a path by which eusociality could evolve by means of multi-level (group) selection in five steps:

1. Formation of groups: Groups could consist of parent-offspring groups or unrelated groups (in situations where cooperation is beneficial) living in a structured nest.
2. Pre-adaptations: Pre-adaptations for social living, such as progressive provisioning, will push the group further toward eusociality.
3. Mutations: Mutations will arise and be selected. Some genes are known to have been silenced in social insect history, leading to the reduction of dispersal behavior and the origin of the wingless caste.
4. Natural Selection Acts on Emergent Traits: The interactions of the individuals can be considered as part of the extended phenotype of the queen. These interactions produce emergent properties upon which natural selection can act.
5. Multi-level selection: More cooperative groups out-compete less cooperative groups.

Nowak's paper, however, received major criticisms for erroneously separating inclusive fitness theory from "standard natural selection". Over 150 authors replied  arguing that Nowak, et al. misrepresent 40 years of empirical literature.

Sociality

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Sociality

 

Gray wolves hunting in a presocial pack encircle an American bison.

Sociality is the degree to which individuals in an animal population tend to associate in social groups (gregariousness) and form cooperative societies.

Sociality is a survival response to evolutionary pressures. For example, when a mother wasp stays near her larvae in the nest, parasites are less likely to eat the larvae. Biologists suspect that pressures from parasites and other predators selected this behavior in wasps of the family Vespidae.

This wasp behaviour evidences the most fundamental characteristic of animal sociality: parental investment. Parental investment is any expenditure of resources (time, energy, social capital) to benefit one's offspring. Parental investment detracts from a parent's capacity to invest in future reproduction and aid to kin (including other offspring). An animal that cares for its young but shows no other sociality traits is said to be subsocial.

An animal that exhibits a high degree of sociality is called a social animal. The highest degree of sociality recognized by sociobiologists is eusociality. A eusocial taxon is one that exhibits overlapping adult generations, reproductive division of labor, cooperative care of young, and—in the most refined cases—a biological caste system.

Presociality

Solitary animals such as the jaguar do not associate except for courtship and mating. If an animal taxon shows a degree of sociality beyond courtship and mating, but lacks any of the characteristics of eusociality, it is said to be presocial. Although presocial species are much more common than eusocial species, eusocial species have disproportionately large populations.

The entomologist Charles D. Michener published a classification system for presociality in 1969, building on the earlier work of Suzanne Batra (who coined the words eusocial and quasisocial in 1966). Michener used these terms in his study of bees, but also saw a need for additional classifications: subsocial, communal, and semisocial. In his use of these words, he did not generalize beyond insects. E. O. Wilson later refined Batra's definition of quasisocial.

Subsociality

Subsociality is common in the animal kingdom. In subsocial taxa, parents care for their young for some length of time. Even if the period of care is very short, the animal is still described as subsocial. If adult animals associate with other adults, they are not called subsocial, but are ranked in some other classification according to their social behaviours. If occasionally associating or nesting with other adults is a taxon's most social behaviour, then members of those populations are said to be solitary but social. See Wilson (1971) for definitions and further sub-classes of varieties of subsociality. Choe & Crespi (1997) and Costa (2006) give readable overviews.

Subsociality is widely distributed among the winged insects, and has evolved independently many times. Insect groups that contain at least some subsocial species are shown in boldface on a phylogenetic tree of the Neoptera (note that many non-subsocial groups are omitted):

Neoptera

Idioprothoraca Embioptera (webspinners) Rhipineoptera Dictyoptera Blattodea (cockroaches, inc. eusocial termites) Mantodea (mantises) Orthoptera (grasshoppers, crickets) Dermaptera (earwigs) Eumetabola Parametabola Zoraptera (angel insects) Paraneoptera Condylognatha Thysanoptera (thrips) Hemiptera (bugs) Membracidae (treehoppers, thorn bugs) Pentatomidae (shield bugs) Reduviidae (predatory bugs) Tingidae (lace bugs) many families Psocoptera (bark lice) Endopterygota Coleoptera Staphylinidae (rove beetles) Silphidae (carrion beetles) Passalidae (bessbugs) Scarabaeidae (scarabs) Tenebrionidae (leaf/flower beetles) Erotylidae (pleasing fungus beetles) Chrysomelidae (leaf beetles) Neuropteroidea Raphidioptera (snakeflies) Neuroptera (lacewings, alderflies, and allies) Antliophora (true flies, scorpionflies, fleas) Trichoptera (caddisflies) Lepidoptera (butterflies and moths) Hymenoptera (sawflies, wasps, ants, bees) (apart from eusocial species)

Solitary but social

The mouse lemur is a nocturnal, solitary-but-social lemur native to Madagascar.

Solitary-but-social animals forage separately, but some individuals sleep in the same location or share nests. The home ranges of females usually overlap, whereas those of males do not. Males usually do not associate with other males, and male offspring are usually evicted upon maturity. However, this is opposite among cassowaries, for example. Among primates, this form of social organization is most common among the nocturnal strepsirrhine species and tarsiers. Solitary-but-social species include mouse lemurs, lorises, and orangutans.

Some individual cetaceans adopt a solitary but social behavior, that is, they live apart from their own species but interact with humans. This behavior has been observed in species including bottlenose dolphin, common dolphin, striped dolphin, beluga, Risso's dolphin, and orca. Notable individuals include Pelorus Jack (1888–1912), Tião (1994–1995), and Fungie (1983–2020). At least 32 solitary-sociable dolphins were recorded between 2008 and 2019.

Parasociality

Not to be confused with parasocial interaction.

Sociobiologists place communal, quasisocial, and semisocial animals into a meta-class: the parasocial. The two commonalities of parasocial taxa are the exhibition of parental investment, and socialization in a single, cooperative dwelling.

Communal, quasisocial, and semisocial groups differ in a few ways. In a communal group, adults cohabit in a single nest site, but they each care for their own young. Quasisocial animals cohabit, but they also share the responsibilities of brood care. (This has been observed in some Hymenoptera and spider taxa, as well as in some other invertebrates.) A semisocial population has the features of communal and quasisocial populations, but they also have a biological caste system that delegates labor according to whether or not an individual is able to reproduce.

Beyond parasociality is eusociality. Eusocial insect societies have all the characteristics of a semisocial one, except overlapping generations of adults cohabit and share in the care of young. This means that more than one adult generation is alive at the same time, and that the older generations also care for the newest offspring.

Eusociality

Main articles: Eusociality and Evolution of eusociality

 

Giant honey bees cover the honeycomb of their nest.

Eusocial societies have overlapping adult generations, cooperative care of young, and division of reproductive labor. When organisms in a species are born with physical characteristics specific to a caste which never changes throughout their lives, this exemplifies the highest acknowledged degree of sociality. Eusociality has evolved in several orders of insects. Common examples of eusociality are from Hymenoptera (ants, bees, sawflies, and wasps) and Blattodea (infraorder Isoptera, termites), but some Coleoptera (such as the beetle Austroplatypus incompertus), Hemiptera (bugs such as Pemphigus spyrothecae), and Thysanoptera (thrips) are described as eusocial. Eusocial species that lack this criterion of morphological caste differentiation are said to be primitively eusocial.

Two potential examples of primitively eusocial mammals are the naked mole-rat and the Damaraland mole-rat (Heterocephalus glaber and Fukomys damarensis, respectively). Both species are diploid and highly inbred, and they aid in raising their siblings and relatives, all of whom are born from a single reproductive queen; they usually live in harsh or limiting environments. A study conducted by O'Riain and Faulkes in 2008 suggests that, due to regular inbreeding avoidance, mole rats sometimes outbreed and establish new colonies when resources are sufficient.

Eusociality has arisen among some crustaceans that live in groups in a restricted area. Synalpheus regalis are snapping shrimp that rely on fortress defense. They live in groups of closely related individuals, amidst tropical reefs and sponges. Each group has one breeding female; she is protected by a large number of male defenders who are armed with enlarged snapping claws. As with other eusocial societies, there is a single shared living space for the colony members, and the non-breeding members act to defend it.

Human eusociality

E. O. Wilson and Bert Hölldobler controversially claimed in 2005 that humans exhibit sufficient sociality to be counted as a eusocial species, and that this enabled them to enjoy spectacular ecological success and dominance over ecological competitors.

Dominance hierarchy

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Dominance_hierarchy

 

A high-ranking male mandrill advertises his status with bright facial coloration.

In biology, a dominance hierarchy (formerly and colloquially called a pecking order) is a type of social hierarchy that arises when members of animal social groups interact, creating a ranking system. A dominant higher-ranking individual is sometimes called an alpha, and the submissive lower-ranking individual a beta. Different types of interactions can result in dominance depending on the species, including ritualized displays of aggression or direct physical violence. In social living groups, members are likely to compete for access to limited resources and mating opportunities. Rather than fighting each time they meet, relative rank is established between individuals of the same sex, with higher-ranking individuals often gaining more access to resources and mates. Based on repetitive interactions, a social order is created that is subject to change each time a dominant animal is challenged by a subordinate one.

Definitions

Dominance is an individual's preferential access to resources over another based on coercive capacity based on strength, threat, and intimidation, compared to prestige (persuasive capacity based on skills, abilities, and knowledge). A dominant animal is one whose sexual, feeding, aggressive, and other behaviour patterns subsequently occur with relatively little influence from other group members. Subordinate animals are opposite; their behaviour is submissive, and can be relatively easily influenced or inhibited by other group members.

Dominance

Wedge-capped capuchins have a clear dominance hierarchy

For many animal societies, an individual's position in the dominance hierarchy corresponds with their opportunities to reproduce. In hierarchically social animals, dominant individuals may exert control over others. For example, in a herd of feral goats it is a large male that is dominant and maintains discipline and coherence of the flock. He leads the group but shares leadership on a foraging expedition with a mature she-goat who will normally outlast a succession of dominant males. However, earlier work showed that leadership orders in goats were not related to age or dominance. In sheep, position in a moving flock is highly correlated with social dominance, but there is no definite study to show consistent voluntary leadership by an individual. In birds, dominant individuals preferentially select higher perches to put themselves in the best position to detect and avoid predators, as well as to display their dominance to other members of their own species. It has been suggested that decision-taking about the actions of the group is commonly dissociated from social dominance.

When individuals seek high rank

Given the benefits and costs of possessing a high rank within a hierarchical group, there are certain characteristics of individuals, groups, and environments that determine whether an individual will benefit from a high rank. These include whether or not high rank gives them access to valuable resources such as mates and food. Age, intelligence, experience, and physical fitness can influence whether or not an individual deems it worthwhile to pursue a higher ranking in the hierarchy, which often comes at the expense of conflict. Hierarchy results from interactions, group dynamics, and sharing of resources, so group size and composition affect the dominance decisions of high-ranking individuals. For example, in a large group with many males, it may be difficult for the highest-ranking male to dominate all the mating opportunities, so some mate sharing probably exists. These opportunities available to subordinates reduce the likelihood of a challenge to the dominant male: mating is no longer an all-or-nothing game and the sharing is enough to placate most subordinates. Another aspect that can determine dominance hierarchies is the environment. In populations of Kenyan vervet monkeys, high-ranking females have higher foraging success when the food resources are clumped, but when food is distributed throughout an area they lose their advantage, because subordinate females can acquire food with less risk of encountering a dominant female.

Benefits

Foraging success

A benefit to high-ranking individuals is increased foraging success and access to food resources. During times of water shortage the highest-ranking vervet females have greater access than subordinates females to water in tree holes. In chacma baboons, the high-ranking males have the first access to vertebrate prey that has been caught by the group, and in yellow baboons the dominant males feed for longer without being interrupted.

In many bird species, the dominant individuals have higher rates of food intake. Such species include dark-eyed juncos and oystercatchers. The dominant individuals in these groups fill themselves up first and fill up more quickly, so they spend less time foraging, which reduces the risk of predation. Thus they have increased survival because of increased nutrition and decreased predation.

Reproductive success

In primates, a well-studied group, high rank brings reproductive success, as seen in a 1991 meta-analysis of 32 studies. A 2016 study determined that higher status increased reproductive success amongst men, and that this did not vary by type of subsistence (foraging, horticulture, pastoralism, agriculture). This contradicts the "egalitarian hypothesis", which predicts that status would affect reproductive success more amongst foragers than amongst nonforagers.

High-ranking bonnet macaque males have more access to fertile females and consequently partake in most of the matings within the group; in one population, three males were responsible for over 75% of matings. In this population, males often vary in rank. As their rank improves, they gain more exclusive time with fertile females; when their rank decreases, they get less time. In many primates, including bonnet macaques and rhesus monkeys, the offspring of high-ranking individuals have better fitness and thus an increased rate of survival. This is most likely a function of two factors: The first is that high-ranking males mate with high-ranking females. Assuming their high rank is correlated with higher fitness and fighting ability, this trait will be conferred to their offspring. The second factor is that higher-ranking parents probably provide better protection to their offspring and thus ensure higher survival rates. Amongst rhesus macaques, higher-ranking males sired more offspring, though the alpha male was never the one to sire the most offspring, with that instead being a high-ranking but not top male. The complex relationship between rank and reproduction in this species is likely explained by the fact that rhesus macaques queue, rather than fight, for dominance, meaning that the alpha male is not necessarily the strongest or most attractive male.

In rodents, the highest-ranking male frequently sires the most offspring. The same pattern is found in most carnivores, such as the dwarf mongoose. The dwarf mongoose lives in a social system with one dominant pair. The dominant female produces all or almost all of the offspring in the living group, and the dominant male has first access to her during her oestrus period. In red deer, the males who experienced winter dominance, resulting from greater access to preferred foraging sites, had higher ability to get and maintain larger harems during the mating season.

In many monogamous bird species, the dominant pairs tend to get the best territories, which in turn promote offspring survival and adult health. In dunnocks, a species of bird that experiences many mating systems, sometimes individuals will form a group that will have one dominant male who achieves all of the mating in the group.

In the monogynous bee species Melipona subnitida, the queen seeks to maintain reproductive success by preventing workers from caring for their cells, pushing or hitting them using her antennae. Workers display aggression towards males, claiming priority over the cells when males try to use them to place eggs.

Costs of being dominant

There are costs to being of a high rank in a hierarchical group which offset the benefits. The most common costs to high-ranking individuals are higher metabolic rates and higher levels of stress hormones. In great tits and pied flycatchers, high-ranking individuals experience higher resting metabolic rates and therefore need to consume more food in order to maintain fitness and activity levels compared to subordinates in their groups. The energetic costs of defending territory, mates, and other resources can be very consuming and cause high-ranking individuals, who spend more time in these activities, to lose body mass over long periods of dominance. Therefore, their physical condition decreases the longer they spend partaking in these high-energy activities, and they lose rank as a function of age.

In wild male baboons, the highest-ranking male, also known as the alpha, experiences high levels of both testosterone and glucocorticoid, which indicates that high-ranking males undergo higher levels of stress which reduces fitness. Reduced health and longevity occurs because these two hormones have immunosuppressant activity, which reduces survival and presents opportunities for parasitic infestation and other health risks. This reduced fitness due to the alpha position results in individuals maintaining high rank for shorter periods of time and having an overall reduced health and longevity from the physical strain and costs of the position.

Interpersonal complementarity hypothesis

Main article: Interpersonal complementarity hypothesis

The interpersonal complementarity hypothesis suggests that obedience and authority are reciprocal, complementary processes. That is, it predicts that one group member's behaviours will elicit a predictable set of actions from other group members. Friendly behaviours are predicted to be met with friendly behaviours, and hostile behaviours are predicted to be reciprocated with similar, hostile behaviours. When an individual acts in a dominant, authoritative manner in a group, this behaviour tends to prompt submissive responses from other group members. Similarly, when group members display submissive behaviour, others feel inclined to display dominant behaviours in return. Tiedens and Fragale (2003) found that hierarchical differentiation plays a significant role in liking behaviour in groups. Individuals prefer to interact with other group members whose power, or status behaviour complements their own. That is to say, group members who behave submissively when talking to someone who appears to be in control are better liked, and similarly individuals who display dominant behaviours (e.g., taking charge, issuing orders) are more liked when interacting with docile, subservient individuals.

Subordinance

Benefits

Being subordinate offers a number of benefits. Subordination is beneficial in agonistic conflicts where rank predicts the outcome of a fight. Less injury will occur if subordinate individuals avoid fighting with higher-ranking individuals who would win a large percentage of the time — knowledge of the pecking order keeps both parties from incurring the costs of a prolonged fight. In hens, it has been observed that both dominants and subordinates benefit from a stable hierarchical environment, because fewer challenges means more resources can be dedicated to laying eggs. In groups of highly related individuals, kin selection may influence the stability of hierarchical dominance. A subordinate individual closely related to the dominant individual may benefit more genetically by assisting the dominant individual to pass on their genes.

Alpha male savanna baboons have high levels of testosterone and stress; over a long period of time, this can lead to decreased fitness. The lowest-ranking males also had high stress levels, suggesting that it is the beta males that gain the most fitness, avoiding stress but receiving some of the benefits of moderate rank. The mating tactics of savanna baboons are correlated with their age. Older, subordinate males form alliances to combat higher-ranking males and get access to females.

Fighting with dominant males is a risky behavior that may result in defeat, injury or even death. In bighorn sheep, however, subordinates occasionally win a fight for a female, and they father 44% of the lambs born in the population. These sheep live in large flocks, and dominance hierarchies are often restructured each breeding season.

Burying beetles, which have a social order involving one dominant male controlling most access to mates, display a behavior known as sneak copulation. While one male at a carcass has a 5:1 mating advantage, subordinate males will tempt females away from the carcass with pheromones and attempt to copulate before the dominant male can drive them forcefully away. In flat lizards, young males take advantage of their underdeveloped secondary sex characteristics to engage in sneak copulations. These young males mimic all the visual signs of a female lizard in order to successfully approach a female and copulate without detection by the dominant male. This strategy does not work at close range because the chemical signals given off by the sneaky males reveal their true nature, and they are chased out by the dominant.

Costs to subordinates

Subordinate individuals suffer a range of costs from dominance hierarchies, one of the most notable being reduced access to food sources. When a resource is obtained, dominant individuals are first to feed as well as taking the longest time. Subordinates also lose out in shelter and nesting sites. Brown hyenas, which display defined linear dominance in both sexes, allow subordinate males and females decreased time of feeding at a carcass. In toque monkeys subordinates are often displaced from feeding sites by dominant males. Additionally, they are excluded from sleeping sites, and they suffer reduced growth and increased mortality.

Subordinate individuals often demonstrate a huge reproductive disadvantage in dominance hierarchies. Among brown hyenas, subordinate females have less opportunity to rear young in the communal den, and thus had decreased survival of offspring when compared to high-ranking individuals. Subordinate males have far less copulations with females compared to the high-ranking males. In African wild dogs which live in social packs separated into male and female hierarchies, top-ranking alpha females have been observed to produce 76–81% of all litters.

Mitigating the costs

Subordinate animals engage in a number of behaviors in order to outweigh the costs of low rank. Dispersal is often associated with increased mortality and subordination may decrease the potential benefits of leaving the group. In the red fox it has been shown that subordinate individuals, given the opportunity to desert, often do not due to the risk of death and the low possibility that they would establish themselves as dominant members in a new group.

Conflict over dominance

Animal decisions regarding involvement in conflict are defined by the interplay between the costs and benefits of agonistic behaviors. When initially developed, game theory, the study of optimal strategies during pair-wise conflict, was grounded in the false assumption that animals engaged in conflict were of equal fighting ability. Modifications, however, have provided increased focus on the differences between the fighting capabilities of animals and raised questions about their evolutionary development. These differences are believed to determine the outcomes of fights, their intensity, and animal decisions to submit or continue fighting. The influence of aggression, threats, and fighting on the strategies of individuals engaged in conflict has proven integral to establishing social hierarchies reflective of dominant-subordinate interactions.

The asymmetries between individuals have been categorized into three types of interactions:

1. Resource-holding potential: Animals that are better able to defend resources often win without much physical contact.
2. Resource value: Animals more invested in a resource are likely to invest more in the fight despite potential for incurring higher costs.
3. Intruder retreats: When participants are of equal fighting ability and competing for a certain territory, the resident of the territory is likely to end as the victor because he values the territory more. This can be explained further by looking at the example of the common shrews. If one participant believes he is the resident of the territory, he will win when the opponent is weaker or food is scarce. However, if both shrews believe they are the true territory holder, the one with the greater need for food, and therefore, the one that values the resource more, is most likely to win.

As expected, the individual who emerges triumphant is rewarded with the dominant status, having demonstrated their physical superiority. However, the costs incurred to the defeated, which include loss of reproductive opportunities and quality food, can hinder the individual's fitness. In order to minimize these losses, animals generally retreat from fighting or displaying fighting ability unless there are obvious cues indicating victory. These often involve characteristics that provide an advantage during agonistic behavior, such as size of body, displays, etc. Red stags, for example, engage in exhausting roaring contests to exhibit their strength. However, such an activity would impose more costs than benefits for unfit stags, and compel them to retreat from the contest. Larger stags have also been known to make lower-frequency threat signals, acting as indicators of body size, strength, and dominance.

Engaging in agonistic behavior can be very costly and thus there are many examples in nature of animals who achieve dominance in more passive ways. In some, the dominance status of an individual is clearly visible, eliminating the need for agonistic behavior. In wintering bird flocks, white-crowned sparrows display a unique white plumage; the higher the percentage of the crown that consists of white feathers, the higher the status of the individual. For other animals, the time spent in the group serves as a determinant of dominance status. Rank may also be acquired from maternal dominance rank. In rhesus monkeys, offspring gain dominance status based on the rank of the mother—the higher ranked the mother, the higher ranked the offspring will be (Yahner). Similarly, the status of a male Canada goose is determined by the rank of his family. Although dominance is determined differently in each case, it is influenced by the relationships between members of social groups.

Regulation mechanisms

Individuals with greater hierarchical status tend to displace those ranked lower from access to space, to food and to mating opportunities. Thus, individuals with higher social status tend to have greater reproductive success by mating more often and having more resources to invest in the survival of offspring. Hence, hierarchy serves as an intrinsic factor for population control, ensuring adequate resources for the dominant individuals and thus preventing widespread starvation. Territorial behavior enhances this effect.

In eusocial animals

The suppression of reproduction by dominant individuals is the most common mechanism that maintains the hierarchy. In eusocial mammals this is mainly achieved by aggressive interactions between the potential reproductive females. In eusocial insects, aggressive interactions are common determinants of reproductive status, such as in the bumblebee Bombus bifarius, the paper wasp Polistes annularis and in the ants Dinoponera australis and D. quadriceps. In general, aggressive interactions are ritualistic and involve antennation (drumming), abdomen curling and very rarely mandible bouts and stinging. The winner of the interaction may walk over the subordinated, that in turn assumes a prostrated posture. To be effective, these regulatory mechanisms must include traits that make an individual rank position readily recognizable by its nestmates. The composition of the lipid layer on the cuticle of social insects is the clue used by nestmates to recognize each other in the colony, and to discover each insect's reproductive status (and rank). Visual cues may also transmit the same information. Paper wasps Polistes dominulus have individual "facial badges" that permit them to recognize each other and to identify the status of each individual. Individuals whose badges were modified by painting were aggressively treated by their nestmates; this makes advertising a false ranking status costly, and may help to suppress such advertising.

Other behaviors are involved in maintaining reproductive status in social insects. The removal of a thoracic sclerite in Diacamma ants inhibits ovary development; the only reproductive individual of this naturally queenless genus is the one that retains its sclerite intact. This individual is called a gamergate, and is responsible for mutilating all the newly emerged females, to maintain its social status. Gamergates of Harpegnathos saltator arise from aggressive interactions, forming a hierarchy of potential reproductives.

In the honey bee Apis mellifera, a pheromone produced by the queen mandibular glands is responsible for inhibiting ovary development in the worker caste. "Worker policing" is an additional mechanism that prevents reproduction by workers, found in bees and ants. Policing may involve oophagy and immobilization of workers who lay eggs. In some ant species such as the carpenter ant Camponotus floridanus, eggs from queens have a peculiar chemical profile that workers can distinguish from worker laid eggs. When worker-laid eggs are found, they are eaten. In some species, such as Pachycondyla obscuricornis, workers may try to escape policing by shuffling their eggs within the egg pile laid by the queen.

Hormonal control

Modulation of hormone levels after hibernation may be associated with dominance hierarchies in the social order of the paper wasp (Polistes dominulus). This depends on the queen (or foundress), possibly involving specific hormones. Laboratory experiments have shown that when foundresses are injected with juvenile hormone, responsible for regulating growth and development in insects including wasps, the foundresses exhibit an increase in dominance. Further, foundresses with larger corpora allata, a region of the female wasp brain responsible for the synthesis and secretion of juvenile hormone, are naturally more dominant. A follow-up experiment utilized 20-hydroxyecdysone, an ecdysone known to enhance maturation and size of oocytes. The size of the oocytes plays a significant role in establishing dominance in the paper wasp. Foundresses treated with 20-hydroxyecdysone showed increased dominance compared to those treated with juvenile hormone, so 20-hydroxyecdysone may play a larger role in establishing dominance (Roseler et al., 1984). Subsequent research however, suggests that juvenile hormone is implicated, though only on certain individuals. When injected with juvenile hormone, larger foundresses showed more mounting behaviors than smaller ones, and more oocytes in their ovaries.

The effect of relative rank on stress hormone levels in savanna baboons

Naked mole-rats (Heterocephalus glaber) similarly have a dominance hierarchy dependent on the highest ranking female (queen) and her ability to suppress critically important reproductive hormones in male and female sub-dominants. In sub-dominant males, it appears that luteinizing hormone and testosterone are suppressed, while in females it appears that the suppression involves the entire suppression of the ovarian cycle. This suppression reduces sexual virility and behavior and thus redirects the sub-dominant's behavior into helping the queen with her offspring, though the mechanisms of how this is accomplished are debated. Former research suggests that primer pheromones secreted by the queen cause direct suppression of these vital reproductive hormones and functions however current evidence suggests that it is not the secretion of pheromones which act to suppress reproductive function but rather the queen's extremely high levels of circulating testosterone, which cause her to exert intense dominance and aggressiveness on the colony and thus "scare" the other mole-rats into submission. Research has shown that removal of the queen from the colony allows the reestablishment of reproductive function in sub-dominant individuals. To see if a priming pheromone secreted by the queen was indeed causing reproductive suppression, researchers removed the queen from the colony but did not remove her bedding. They reasoned that if a primer pheromones were on the bedding then the sub-dominant's reproductive function should continue to be suppressed. Instead however, they found that the sub-dominants quickly regained reproductive function even in the presence of the queen's bedding and thus it was concluded that primer pheromones do not seem to play a role in suppressing reproductive function.

Glucocorticoids, signaling molecules which stimulate the fight or flight response, may be implicated in dominance hierarchies. Higher ranking individuals tend to have much higher levels of circulating glucocorticoids than subdominant individuals, the opposite of what had been expected. Two core hypotheses attempt to explain this. The first suggests that higher ranking individuals exert more energy and thus need higher levels of glucocorticoids to mobilize glycogen for energy use. This is supported by the fact that when food availability is low, cortisol levels increase within the dominant male. The second suggests that elevated stress hormones are a result of social factors, particularly when the hierarchy is in transition, perhaps resulting in increased aggression and confrontation. As a result, the dominant individual fights more and has elevated glucocorticoids during this period. Field studies of olive baboons in Kenya seem to support this, as dominant individuals had lower cortisol levels in a stable hierarchy than did subdominant individuals, but the reverse was true at unstable times.

Brain pathways and hierarchy

Several areas of the brain contribute to hierarchical behavior in animals. One of the areas that has been linked with this behavior is the prefrontal cortex, a region involved with decision making and social behavior. High social rank in a hierarchical group of mice has been associated with increased excitability in the medial prefrontal cortex of pyramidal neurons, the primary excitatory cell type of the brain. High ranking macaques have a larger rostral prefrontal cortex in large social groups. Neuroimaging studies with computer stimulated hierarchal conditions showed increased activity in the ventral and dorsolateral prefrontal cortex, one processing judgment cues and the other processing status of an individual. Other studies have determined that lesions to the prefrontal cortex (when the area is severed to disrupt functioning to observe its role in behavior) led to deficits in processing social hierarchy cues, suggesting this area is important in regulating this information. Although the prefrontal cortex has been implicated, there are other downstream targets of the prefrontal cortex that have also been linked in maintaining this behavior. This includes the amygdala through lesion studies in rats and primates which led to disruption in hierarchy, and can affect the individual negatively or positively depending on the subnuclei that is targeted. Additionally, the dorsal medial PFC-medial dorsal thalamus connection has been linked with maintenance of rank in mice. Another area that has been associated is the dorsal raphe nucleus, the primary serotonergic nuclei (a neurotransmitter involved with many behaviors including reward and learning). In manipulation studies of this region, there were changes in fighting and affiliative behavior in primates and crustaceans.

In specific groups

Main article: List of dominance hierarchy species

Female dominance in mammals

The bonobo is one of the few mammals with female-biased dominance.

Female-biased dominance occurs rarely in mammals. It occurs when all adult males exhibit submissive behavior to adult females in social settings. These social settings are usually related to feeding, grooming, and sleeping site priority. It is observed consistently in hyenas, lemurs and the bonobo. The ring-tailed lemur is observed to be the most prominent model of female dominance.

There are three basic proposals for the evolution of female dominance:

1. The Energy Conservation Hypothesis: males subordinate to females to conserve energy for intense male-male competition experienced during very short breeding seasons
2. Female behavioral strategy: dominance helps females deal with the unusually high reproductive demands; they prevail in more social conflicts because they have more at stake in terms of fitness.
3. Male behavioral strategy: males defer as a parental investment because it ensures more resources in a harsh unpredictable climate for the female, and thus, the male's future offspring.

In lemurs, no single hypothesis fully explains female social dominance at this time and all three are likely to play a role. Adult female lemurs have increased concentrations of androgens when they transition from non-breeding to breeding seasons, increasing female aggression. Androgens are greater in pregnant female lemurs, which suggests that organizational androgens might influence the developing offspring. Organizational androgens play a role in "explaining female social dominance" in ring-tailed lemurs, as androgens are associated with aggressive behavior in young females. Females that were "exposed to greater concentrations of maternal [androstenedione] late in fetal development were less likely to be aggressed against postnatally, whereas females that were...exposed to greater concentrations of maternal [testosterone]...were more likely to receive aggression postnatally." Dominance rank in female chimpanzees is correlated with reproductive success. Although a high rank is an advantage for females, clear linear hierarchies in female chimpanzees have not been detected. In "masculinized" female mammals like the spotted hyena (Crocuta crocuta), androgens (i.e. specifically, androstenedione and testosterone) are "implicated in the organization and activation of...nonreproductive behavioral traits, including aggression, social dominance, rough-and-tumble play, and scent marking" For aggressively dominant female meerkats (Suricata suricatta), they have "exceptionally high concentrations" of androgens, "particularly during gestation".

Birds

Bottom-rank chicken showing feather damage from pecking by other hens

The concept of dominance, originally called "pecking order", was described in birds by Thorleif Schjelderup-Ebbe in 1921 under the German terms Hackordnung or Hackliste and introduced into English in 1927. In his 1924 German-language article, he noted that "defense and aggression in the hen is accomplished with the beak". This emphasis on pecking led many subsequent studies on fowl behaviour to use it as a primary observation; however, it has been noted that roosters tend to leap and use their claws in conflicts.

Wild and feral chickens form relatively small groups, usually including no more than 10 to 20 individuals. It has been shown that in larger groups, which is common in farming, the dominance hierarchy becomes less stable and aggression increases.

Dominance hierarchies are found in many species of bird. For example, the blue-footed booby brood of two chicks always has a dominance hierarchy due to the asynchronous hatching of the eggs. One egg is laid four days before the other, and incubation starts immediately after laying, so the elder chick is hatched four days before the younger chick and has a four-day head start on growth. The elder, stronger chick almost always becomes the dominant chick. During times of food shortage, the dominant chick often kills the subordinate chick by either repeatedly pecking or by ousting the younger chick from the nest. The brood hierarchy makes it easier for the subordinate chick to die quietly in times of food scarcity, which provides an efficient system for booby parents to maximize their investment.

Eusocial insects

In insect societies, only one to few individuals members of a colony can reproduce, whereas the other colony members have their reproductive capabilities suppressed. This conflict over reproduction in some cases results in a dominance hierarchy. Dominant individuals in this case are known as queens and have the obvious advantage of performing reproduction and benefiting from all the tasks performed by their subordinates, the worker caste (foraging, nest maintenance, nest defense, brood care and thermal regulation). According to Hamilton's rule, the reproduction costs of the worker caste are compensated by the contribution of workers to the queen's reproductive success, with which they share genes. This is true not only for the popular social insects (ants, termites, some bees and wasps), but also for the naked mole-rat Heterocephalus glaber. In a laboratory experiment, Clarke and Faulkes (1997) demonstrated that reproductive status in a colony of H. glaber was correlated with the individual's ranking position within a dominance hierarchy, but aggression between potential reproductives only started after the queen was removed.

The social insects mentioned above, excluding termites, are haplodiploid. Queen and workers are diploid, but males develop from haploid genotypes. In some species, suppression of ovary development is not totally achieved in the worker caste, which opens the possibility of reproduction by workers. Since nuptial flights are seasonal and workers are wingless, workers are almost always non-breeders, and (as gamergate ants or laying worker bees) can only lay unfertilised eggs. These eggs are in general viable, developing into males. A worker that performs reproduction is considered a "cheater" within the colony, because its success in leaving descendants becomes disproportionally larger, compared to its sisters and mother. The advantage of remaining functionally sterile is only accomplished if every worker assume this "compromise". When one or more workers start reproducing, the "social contract" is destroyed and the colony cohesion is dissolved. Aggressive behavior derived from this conflict may result in the formation of hierarchies, and attempts of reproduction by workers are actively suppressed. In some wasps, such as Polistes fuscatus, instead of not laying eggs, the female workers begin being able to reproduce, but once being under the presence of dominant females, the subordinate female workers can no longer reproduce.

In some wasp species such as Liostenogaster flavolineata there are many possible queens that inhabit a nest, but only one can be queen at a time. When a queen dies the next queen is selected by an age-based dominance hierarchy. This is also true in the species Polistes instabilis, where the next queen is selected based on age rather than size. Polistes exclamans also exhibits this type of hierarchy. Within the dominance hierarchies of the Polistes versicolor, however, the dominant-subordinate context in the yellow paper wasps is directly related to the exchange of food. Future foundresses within the nest compete over the shared resources of nourishment, such as protein. Unequal nourishment is often what leads to the size differences that result in dominant-subordinate position rankings. Therefore, if during the winter aggregate, the female is able to obtain greater access to food, the female could thus reach a dominant position.

In some species, especially in ants, more than one queen can be found in the same colony, a condition called polygyny. In this case, another advantage of maintaining a hierarchy is to prolong the colony lifespan. The top ranked individuals may die or lose fertility and "extra queens" may benefit from starting a colony in the same site or nest. This advantage is critical in some ecological contexts, such as in situations where nesting sites are limited or dispersal of individuals is risky due to high rates of predation. This polygynous behavior has also been observed in some eusocial bees such as Schwarziana quadripunctata. In this species, multiple queens of varying sizes are present. The larger, physogastric, queens typically control the nest, though a "dwarf" queen will take its place in the case of a premature death.

Variations

Spectrum of social systems

Dominance hierarchies emerge as a result of intersexual and intrasexual selection within groups, where competition between individuals results in differential access to resources and mating opportunities. This can be mapped across a spectrum of social organization ranging from egalitarian to despotic, varying across multiple dimensions of cooperation and competition in between. Conflict can be resolved in multiple ways, including aggression, tolerance, and avoidance. These are produced by social decision-making, described in the "relational model" created by the zoologist Frans De Waal. In systems where competition between and within the sexes is low, social behaviour gravitates towards tolerance and egalitarianism, such as that found in woolley spider monkeys. In despotic systems where competition is high, one or two members are dominant while all other members of the living group are equally submissive, as seen in Japanese and rhesus macaques, leopard geckos, dwarf hamsters, gorillas, the cichlid Neolamprologus pulcher, and African wild dog. Linear ranking systems, or "pecking orders", which tend to fall in between egalitarianism and despotism, follow a structure where every member of the group is recognized as either dominant or submissive relative to every other member. This results in a linear distribution of rank, as seen in spotted hyenas and brown hyenas.

Context dependency

Eringer cattle competing for dominance.

Dominance and its organisation can be highly variable depending on the context or individuals involved. In European badgers, dominance relationships may vary with time as individuals age, gain or lose social status, or change their reproductive condition. Dominance may also vary across space in territorial animals as territory owners are often dominant over all others in their own territory but submissive elsewhere, or dependent on the resource. Even with these factors held constant, perfect dominance hierarchies are rarely found in groups of any great size, at least in the wild. Dominance hierarchies in small herds of domestic horses are generally linear hierarchies whereas in large herds the relationships are triangular. Dominance hierarchies can be formed at a very early age. Domestic piglets are highly precocious and, within minutes of being born, or sometimes seconds, will attempt to suckle. The piglets are born with sharp teeth and fight to develop a teat order as the anterior teats produce a greater quantity of milk. Once established, this teat order remains stable with each piglet tending to feed from a particular teat or group of teats. Dominance–subordination relationships can vary markedly between breeds of the same species. Studies on Merinos and Border Leicesters sheep revealed an almost linear hierarchy in the Merinos but a less rigid structure in the Border Leicesters when a competitive feeding situation was created.

Species with egalitarian/non-linear hierarchies

Although many group-living animal species have a hierarchy of some form, some species have more fluid and flexible social groupings, where rank does not need to be rigidly enforced, and low-ranking group members may enjoy a wider degree of social flexibility. Some animal societies are "democratic", with low-ranking group members being able to influence which group member is leader and which one is not. Sometimes dominant animals must maintain alliances with subordinates and grant them favours to receive their support in order to retain their dominant rank. In chimpanzees, the alpha male may need to tolerate lower-ranking group members hovering near fertile females or taking portions of his meals. Other examples can include Muriqui monkeys. Within their groups, there is abundant food and females will mate promiscuously. Because of this, males gain very little in fighting over females, who are, in turn, too large and strong for males to monopolize or control, so males do not appear to form especially prominent ranks between them, with several males mating with the same female in view of each other. This type of mating style is also present in manatees, removing their need to engage in serious fighting. Among female elephants, leadership roles are not acquired by sheer brute force, but instead through seniority, and other females can collectively show preferences for where the herd can travel. In hamadryas baboons, several high-ranking males will share a similar rank, with no single male being an absolute leader. Female bats also have a somewhat fluid social structure, in which rank is not strongly enforced. Bonobos are matriarchal, yet their social groups are also generally quite flexible, and serious aggression is quite rare between them. In olive baboons, certain animals are dominant in certain contexts, but not in others. Prime age male olive baboons claim feeding priority, yet baboons of any age or sex can initiate and govern the group's collective movements.