Can Evolutionary Principles Explain Patterns of Family Violence?John Archer

Archer, J. (2013). Can evolutionary principles explain patterns of family violence? Psychological Bulletin, 139(2), 403-440. doi:10.1037/a0029114

Summary

Introduction

Violence within families is an important field of study and has wide reaching societal implications. Most existing research into family violence has its roots in conventional science, but the aim of this analysis was to approach family violence from an evolutionary perspective. This makes sense, because families find their origin in the evolutionary heritage of human species. An additional benefit of analyzing family violence from an evolutionary perspective lies in the fact that we are able to analyze the families of animals other than humans. The paper begins by outlining and analyzing various evolutionary constructs that are pertinent to family violence as well as predictions for how the constructs will influence family violence. The second part of the paper focuses on the application of evolutionary principles to violence between parents, offspring, and siblings. The third part of the paper focuses on violence between sexual partners. The focus throughout the paper remains on violent acts, which is a subset of aggression. Specifically, the article focuses on non-sexual physical violence.

Evolutionary Principles and Family Violence

The evolutionary principles that Archer applies to family violence fall under two variables: shared kinship and reproductive value (RV). Both of these variables consider how age, resources, and offspring quality affect the degree of kinship felt with another. Consequently, based off the degree of kinship felt with another, these variables will affect the degree to which conflict is likely. Another variable, resource-holding power (RHP), and concerns the judgment of characteristics of individuals involved in conflict.

Kin Selection and Hamilton’s Rule

Kin are generally more likely than unrelated individuals to cooperate and less likely to compete, because altruistic behavior to relatives provides a way of perpetuating shared genes. This concept was demonstrated by W.D. Hamilton (1964) in his model of evolution of altruistic behavior among kin. Hamilton also pioneered the concept of inclusive fitness, which focuses on interactions among individuals who share the same genes. In line with this perspective, parental care of offspring is a special case of kin behavior because parents share an average of 50% of their genes with kin. Hamilton introduced the Hamilton’s Rule (D.M. Buss, 1999, 2011), which is an analysis of evolutionary costs and benefits related to degree of relatedness. In

Hamilton’s rule, the benefits of helping an individual are multiplied by the degree of relatedness, and compared to the costs of helping. If the benefits X the degree of relatedness exceed the cost, helping behavior is likely to occur. An obvious prediction about family violence stemming from Hamilton’s rule is that there is more likely to be violence in families composed of non-genetic relatedness, because the degree of relatedness is 0.

Kin Recognition

To be able to accurately respond to kin, animals must first be able to differentiate kin from non-kin. One mechanism by which animals are able to differentiate is through shared rearing. If an animal knows it gave birth to another animal, kinship is assured. Another mechanism of accurately assessing kinship is facial recognition. Animals are able to use visual cues residing in facial similarity to assess the agree of similarity to oneself. Humans are also able to use odor to detect kin. Mothers are able to detect a child’s odor but not that of a stepchild.

Reproductive Value (RV)

The principle of reproductive value (RV) (Fisher, 1930) refers to the contribution to a related individual’s fitness at different ages RV is a measure of the degree to which individuals of a particular age are likely to contribute, in terms of offspring, to future generations. As offspring grow older, their RV increases because they are nearing the age at which they will be able to reproduce and pass on the parent’s genes. As parents grow older, their RV decreases because they are leaving the window of time in which they can reproduce. Archer theorizes that because of this, offspring will be the most at risk of violence when they are young and their RV is low. Conversely, Archer theorizes that adults will be most at risk from violence by offspring as they grow older, because their RV is declining.

Resource Holding Power (RHP)

In a game theory model of evolutionary fighting, G.A. Parker (1974) demonstrated that when in conflict, animals assess each others fighting ability and act on this information. Animals that are accurately able to assess an opponents fighting ability and react accordingly – fight or flee – are more likely to be selected and pass on genes. Parker referred to fighting ability as RHP, and assessing fighting ability and acting accordingly is an evolutionarily stable strategy (ESS; Maynard Smith, 1982). In line with these findings, size and other fighting ability cues predict which of two opponents is likely to initiate and win a confrontation (Archer, 1988; Archer & Huntingford, 1994; Arnott & Elwood, 2009). The principle of RHP is one that can also clearly be applied to family violence. Throughout the majority of childhood and adolescence, parents will have higher RHP than their offspring. However, eventually the RHP hierarchy will be reversed when the offspring come of age and the parents RHP is on the decline. Archer predicts that this reversal will be apparent in data on child abuse by parents and parent abuse by offspring.

Violence Between Parents, Offspring, and Siblings

The principles covered thus far and hypothesis derived from them are illustrated in the table above. Archer begins by analyzing violence toward stepchildren, and then moves on to violence by genetic parents, by offspring toward parents, and between siblings.

Parental Violence to Unrelated Children

Families in which one of the parents is unrelated to the children occur frequently in western society. The main evolutionary principle to be applied to family violence in

this situation is the fact that there will be a higher rate of abuse from a stepparent than from a genetic child due to the fact that the stepparent will have no degree of genetic relatedness to the child. Earlier studies confirm this idea and found higher than expected rates of child abuse and homicide in stepparent families (Fergusson, Fleming & O’neill, 1972; Gil, 1970; Scott, 1973). The evidence, summarized in the table blow, indicates that stepparent households are at a much higher risk of violence for children than genetic parent households. Killings by stepparents are more likely to involve hostile actions rather than instrumental actions. These findings have been explained in terms of inclusive fitness as an ultimate variable and use parental bonding as a proximate mechanism (Daly & Wilson, 1981b, 1985, 1988; Wilson et al., 1980). Attachment theory is also thought to be a causal mechanism for the increase in violence.

Parental Violence to Genetic Children

The primary evolutionary construct involved in violence between parents and genetic offspring is the parent-offspring conflict model (Trivers, 1974). The parent offspring conflict model predicts that conflicts arise between parents and offspring when the offspring seek more resources than the parent is able to provide. Archer also points out three additional evolutionary principles involved in parent and genetic offspring violence. 1: The reproductive value of the child, or RVc. The RVc is low in early years, and increases as the child gets older. The main prediction from RVc is that the risk of abuse and neglect by parents is higher in the offspring’s early years but declines as the child grows older. Archer also predicts that the risk of abuse and violence will be more pronounced when infant quality is low and parental resources are scarce. 2: The RV of the parent, or RVp. As the RVp goes down, parents will value their offspring more. The prediction is therefore that as RVp decreases, the risk of child abuse will decline. 3: Paternity uncertainty, which predicts that there will be more abuse by fathers where their paternity is uncertain. The table below summarizes the predictions along with the evidence for these

claims:

Offspring Violence to Parents

As an offspring’s RV (RVc) increases during childhood, the offspring’s contribute to its parent’s inclusive fitness increases. Simultaneously, the parents RV (RVp) is declining, so the parents contribution to the child’s fitness decreases. According to Daly and Wilson (1988, p. 99) this is one reason why older offspring are more likely to kill their parents than their parents are to kill them. At some point there will be a crossover of parent RV and offspring RV, as shown in this figure:

The prediction of offspring violence to parents solely based off RV is that parents will be at the highest risk of violence as the offspring grows older. There will also be another crossover as the offspring grows older, that of RHP. As the child grows older he/she will attain more and more RHP, and the parents RHP will decline. The RHP crossover point is theorized to be later in life than the RV crossover point. Based solely on RHP, it would be expected that there will be more violence to parents from boys than girls. A son’s violence to his father might show an increase in his late teenage years as he acquires more strength. Mothers were found to be more likely the victims of children’s physical aggression from police reports. It is likely that this is not only due to a greater RHP disparity from mother to son than

father to son, but also the fact that children spend more time with their mothers than fathers. The predicted increase in physical aggression by sons to fathers was found in three US studies. It was also found that the rate of violence by offspring to parents is greater in non-genetically related families. However, it is clear that the hypothesis derived from RV and RHP cannot explain offspring violence to parents alone as demonstrated by the table below:

Violence Between Siblings

According to the principles of inclusive fitness, human siblings will have less conflict than unrelated individuals in similar situations. Additionally, because siblings will most likely have different levels of strength at different times, Archer predicts that older siblings (who presumably have higher RHP) will dominate younger ones (who have lower RHP). Archer predicts the following: that conflict between siblings will be common but generally at low levels; that conflict will escalate when resources are scarce or where there is a large inheritance to be distributed unequally; that close kin such as siblings are likely to cooperate in aggression aimed at unrelated individuals; that physical aggression will be more common between step than genetic siblings, and that older siblings will show more aggression to younger ones

than vice versa. The Table below summarizes the predictions and outcomes:

It was found that any form of physical aggression between siblings was more common than other forms of family violence, and that more serious disputes (when they did occur) occurred from 14 to 17 years of age. Sibling homicide was uncommon and tended to happen in adulthood over inheritance. It was found that siblings had a greater tendency to cooperate and kill an unrelated individual. A single study found that there was more physical aggression among stepsiblings than genetic siblings. Concerning RHP, older siblings showed more violence and were more likely to initiate conflict than younger siblings. However, most often the age difference and increase in RHP held by the older sibling was often mitigated by parental intervention.

Violence Between Sexual Partners

The application of evolutionary principles to partner relations focuses on paternity uncertainty and the males interactions with the female regarding unnasured paternity. Because of the fact that the male may be unsure of paternity, the argument is that he has evolved counter measures, in the form of “mate guarding”, to attempt to ensure paternity certainty. According to Wilson and Daly (1992, 1998) mate guarding is associated with a male mindset that gave rise to a variety of cultural beliefs and practices. Examples of these beliefs and practices are the valuation of female chastity, the double standard in regard to adultery, and general restrictions on the activities of women. Although partner conflict can arise because of other issues, such as allocation of resources, most evolutionary analysis on partner violence focuses on male controlling behavior, which has evolved as a result of paternity uncertainty. (Goetz, Shackelford, Romero, Kaighobadi, & Miner, 2008). Consequently, Archer predicts that: it will be mainly male to female violence since there is no maternity uncertainty; that men should seek to control their partner’s activities, particularly their access to other men, and that controlling behavior will be linked to men’s but not women’s partner aggression. The findings are

summarized in a table below:

The findings conclude that there is an absence of a sex difference in physical aggression among partners. The pattern of male to female physical aggression is only found in low gender-empowerment nations, yet paternity uncertainty is a factor regardless of culture. Additionally, there were similar levels of jealousy found irrespective of sex. The findings conclude that both sexes are motivated to control their partners and are likely to use violence as a form of control.

Summary and Conclusions

Kin Selection

Kin selection led to a range of predictions, the centermost being that there would be a greater risk of violence toward non-genetic children. Archer found that 20 different studies indicate a higher risk of abuse and homicide among non-genetic families.

Reproductive Value

The prediction that violence would be at its highest when offspring’s RV was at its lowest was supported both for violence and homicide. Similarly, if the offspring was thought of as having poor physical prospects or there was a shortage of resources in the family, both of which were linked to low offspring RV, there was a higher risk of homicide or abuse in the family. Archer made two predictions based on the decline of parental RV with age: the first being that the risk of violence to parental offspring would decline, and the second being that the risk of violence from offspring to parent would increase. Both of these predictions were supported in the data.

OutlineIntroduction

1. Evolutionary Principles of family violencea. Kin selection and Hamilton’s ruleb. Kin recognitionc. Reproductive value (RV)d. Attachment and selective investmente. Resource holding power

Violence between parents, offspring, and siblings1. Parental violence to unrelated children

a. Background and predictionsb. Evidencec. Discussion and conclusions

2. Parental violence to genetic childrena. Background and predictionsb. Evidencec. Discussion and conclusions

3. Offspring’s violence to parentsa. Background and predictionsb. Evidencec. Discussion and conclusions

4. Violence between siblingsa. Background and predictionsb. Evidencec. Discussion and conclusions

Violence Between Sexual partners1. Partner violence as mate guarding

a. Background and predictionsb. Evidencec. Discussion and conclusions

2. Partner violence in relation to other evolutionary predictionsa. Background and predictionsb. Evidencec. Discussion and conclusions

3. Conflicts of interest and coercive powera. Background and predictionsb. Evidencec. Discussion and conclusions

Summary and Conclusions1. Kin selection2. Reproductive value3. Resource holding power

Future Directions

Critical Review

Points we disagreed with:

The main critical point that comes up for me with the article lies in the possibility of confounds. On one hand we could say that evolutionary principles are causing family violence, but can we truly say that evolutionary principles are the only cause. There are a multitude of other factors that affect a family at any given time, and they can’t be ruled out of analysis. An example being: perhaps stepparents are more violence prone than genetic parents, rather than responding to the factors that come with having a stepchild.

Another critical point lies in the populations surveyed. Most of the data used comes from modern Western Nations. Families all over the world have unique structures and values, and consequently I have to believe that they also have different data on family violence. In order to accurately get a picture of how evolutionary principles might relate to family violence, more families coming from more varied cultures should be surveyed.

Another area that we found to be lacking was the lack of data in some areas. The author found only one study confirming violence between siblings. The sample simply isn’t large enough to make a conclusion. And the majority of the data that is used comes from police reports. There are no doubt thousands of cases of domestic violence that go unreported to the police, but they are still valid data points nonetheless.

Points we found interesting

The idea that siblings are more likely to commit homicide as a team against unrelated individuals due to the principles of kin selection is an interesting idea.

We also liked the idea of resource holding power, or RHP. However, it’s clear that RHP was originally meant as a variable in the ancestral environment. For our ancestors, strength and size were key factors in controlling and holding resources. In today’s society, you don’t need to be strong to have resources, so it seems like RHP is an outdated concept. It would be interesting to see resource holding potential evaluated in a new light. For an example, does a successful CEO have more resource holding potential than a professional bodybuilder? If you look at the facts, the CEO probably holds more resources than the bodybuilder, but probably isn’t as strong or large of a person.

Another interesting point was the crossover of reproductive value that occurs as parents and children age. As one person RV declines (the parents) the other increases (the child).

Multiple Choice Questions

True/False

Violence is common between siblings, but genetic siblings are more likely to commit homicide against unrelated individuals T/F

There is more violence between partners from male’s to females than females to males T/F

Violence is more likely to occur in families that aren’t genetically related compared to genetically related families T/F

Multiple Choice

Resource holding potential refers to…A)accurately evaluating the fighting ability of an opponentB)how many resources an individual controlsC)the gender of an opponentD)what kind of resources another individual possesses

Reproductive value refers to…A) How sexually active an individual isB) How many offspring an individual can haveC) An individual’s benefit to the evolutionary fitness of another

Kin recognition can function by…A)Recognizing odorB) Recognizing facial resemblanceC) Recognizing muscle toneD) Both A & B