How Biological Psychology Studies Genetic Makeup
De Paul Law Rev. Author manuscript; available in PMC 2015 Dec 21.
Published in terminal edited form as:
De Paul Law Rev. 2007 Spring; 56(three): 837–846.
PMCID: PMC4685725
NIHMSID: NIHMS741938
THE BIOLOGY OF RELATIONSHIPS: WHAT BEHAVIORAL GENETICS TELLS United states Almost INTERACTIONS AMONG FAMILY MEMBERS
Laura A. Baker
*Department of Psychology, University of Southern California
Introduction
Human behavior is subject to genetic variations. The ways in which individuals differ in their intellectual abilities, personalities, and mental wellness are, to a large extent, functions of their inherited genetic predispositions. Decades of inquiry on twins, adoptees, and families have led to the inescapable conclusion that about reliably measured psychological characteristics are influenced to some degree by genes. Behavior too shows signs of genetic influence; the way 1 experiences stressful life events, for example, shows some genetic influence. Even personal aspects of individuals, such as spirituality and political ideology, are affected to an extent by genes.1 Information technology should come up every bit no surprise, and then, that genes influence the means in which families part and how family unit members relate to ane another.two Familial relationships of all kinds—parent-kid, sibling, and spousal—tin exist shown to be at least partially the product of genetic factors.
This Article discusses a behavioral genetic perspective that provides insight into the biological factors that influence family relationships. Part Ii presents a brief overview of the research methods used to sympathise both genetic and environmental influences on homo behavior. Function Three then discusses several central findings from the field of behavioral sciences, particularly how they pertain to the means in which family members relate to one another. Information technology focuses on the post-obit: (1) characteristics of parents and variations in the ways they treat their ain children; (two) characteristics of children and how they may react to their parents' behavior; and (3) the interactive processes that occur betwixt parents and children. While the primary focus of Part Three is on parent-child relationships, Part IV considers sibling and spousal relationships. Part V discusses the full general interpretation of family relationships from a behavioral genetic perspective.
II. Twin, Family, and Adoption Studies
What is the evidence for the overwhelming influence of genetic factors on human psychological part? What does it mean to say that psychological dimensions of family relations are a function of genes? Answering these questions requires a basic understanding of behavioral genetic studies, which help to separate the effects of genes and surround in human behavior.
The general strategy in behavioral-genetic research designs involves the report of family unit members with varying degrees of genetic and environmental relatedness.iii For instance, genetic influences in a trait are evident if pairs of monozygotic (MZ) twins (who are genetically identical) are more similar to one some other than dizygotic (DZ) twins (who share only about 50% of their genes), or if pairs of biological siblings raised together resemble 1 another more than than unrelated (e.grand., adoptive) siblings raised together. In full general, if psychological traits and observed beliefs have a genetic component, then genetically similar relatives should resemble one another more closely than individuals who share fewer genes.four
Regarding environmental influences, researchers in behavioral genetics typically distinguish between ii broad classes of effects: (1) environmental factors shared past relatives that cause them to behave similarly; and (ii) unique, individual environments that are not shared by relatives, which crusade them to be different from ane another. These are referred to, respectively, as shared and nonshared environments. Shared environmental influences are axiomatic when greater trait similarity is observed for those relatives who share more experiences (east.g., siblings raised together rather than apart), or when twins are more similar to one another than their genetic relatedness would predict. Bear witness for nonshared surroundings often stems from differences observed betwixt genetic relatives—that is, their lack of resemblance. Differences between MZ co-twins, for example, must stem from nonshared environments. The written report of the similarities and differences betwixt relatives of varying degrees of genetic and ecology relatedness provide the bones data for understanding the effects of genes, and thus the influence of shared and nonshared environments on behavior.five
Within a few decades of the primeval twin, family, and adoption studies (which grew immensely from the 1970s onward), genetic factors were implicated in a wide range of homo behaviors, such as cognitive power and personality, equally well as most major psychological disorders, such as depression and schizophrenia.half-dozen Collectively, these studies show that family members who are more closely related genetically demonstrate greater similarity than unrelated individuals for measured aspects of personality (e.grand., extraversion or neuroticism), intellectual function (e.g., verbal skills and spatial power), and likelihood of beingness diagnosed with a psychological disorder (eastward.one thousand., depression or schizophrenia).7
For a while, it was considered a challenge to find an indelible aspect of behavior that did not appear to be influenced by genes. Constructs such equally religious behaviors and political attitudes, which had traditionally been understood to exist strictly the product of civilization, became the subject of behavioral genetic studies. Somewhat surprisingly, fifty-fifty these culturally defined behaviors announced to be influenced by genetic variations, at least inside groups of individuals. For example, although one'southward religion may be culturally defined and thus independent of genetic influences, the degree to which one engages in the rituals or adheres to the tenets of a item religion appear to be affected by one's genetic inheritance.8 Indeed, even the degree to which an individual may endorse highly liberal or conservative ideals (e.g., abortion rights or gay rights) has been shown to exist influenced by genetic factors; MZ twins are much more similar than DZ twins, and biological siblings are more similar than adoptive siblings in conservative attitudes from adolescence onward.9
Around the same time these culturally divers behaviors became the subject of behavioral genetic research, investigators began to written report other variables that were traditionally viewed as entirely "environmental" factors. This research challenged a long-continuing social learning perspective in developmental psychology. What were traditionally considered to be "ecology" measures—including aspects of parenting—came to be understood as products of both genes and surround. Thus, we plow dorsum at present to the issue at hand: the various aspects of family relationships and how they are influenced by the complex interplay between genes and environment.
III. How the Behavior of Parents and children Is Influenced by Genes and Environs
Genes influence each private'southward behavioral and psychological characteristics, including intellectual ability, personality, and chance for mental illness—all of which have bearing on both parents and children within a family. The means in which genes and environment can affect parent-child relationships tin be seen in Figure i. This model represents a standard manner in which behavioral geneticists retrieve about human behavior in the context of family unit relationships. Parents' genes influence their ain beliefs (including the ways they parent their children) and children's genes influence their own beliefs (including the ways they respond to their parents). The transmission of genes from parent to child is one of import link that will pb to similarities between the behavior of a parent and a child. For example, to the extent that genes predispose an individual toward aggressive beliefs, including violence toward others, parents and children will testify similarities in this expanse of behavior. This might offer some other explanation for the "cycle of violence" in which abusive parenting is related to assailment and other hating behaviors in children.10 Antisocial behavior does, in fact, show moderate genetic influence in a wide range of studies.11
Behavioral Genetic Model of Parent-Kid Behavior
Besides directly genetic transmission, the model in Figure 1 indicates 2 other important ways in which the behavior of parents and children may exist linked. First, parental beliefs may itself be an important attribute of the child's surround, which may be considered a form of "cultural transmission." For example, a mother's intelligence, personality, and mental health may accept an impact on the child'due south environment; mothers with higher intelligence and education spend more time reading to their children and engaging them in stimulating activities.12 Importantly, however, these characteristics may each be influenced by the mother'southward genetic makeup, and thus it can be seen how the mother's genotype may ultimately exist associated with the child'due south environs. The association between genes and environment is generally referred to as a genotype-surround correlation (rGE). One mode in which rGE may ascend is through this passive grade of cultural transmission, which is referred to as a passive rGE.13
The third link between the behavior of parents and children is established through the "evocative responses" that children'due south behavior may elicit from their parents. Considering a child's behavior is itself influenced by the child's genes, genetically different children living in the same family may arm-twist different parenting responses. This may outcome in another form of a genotype-environment correlation, an rGE of an evocative form.14 That is, genetically based differences among children (due east.g., temperament characteristics) may evoke different responses from their parents (e.thou., disciplinary styles). Thus, genes and environment may be intertwined in complex ways within parent-child relationships.
These complexities can be unraveled by twin, family, and adoption studies. Genetic influences on parenting beliefs tin can be understood by examining the similarities and differences in developed twins' parenting styles. The parenting styles of adult twins—every bit measured by positivity, negativity, and monitoring of their children—were more highly correlated for MZ than DZ twins.15 Reviews of other studies show similar patterns, in which parents' genes influence the ways in which they parent their children.16
Evidence of parental behaviors evoked by children has been demonstrated past studying how parents respond differently to two or more children in the same family, such equally twins and other siblings. DZ twin children, for case, take reported more differences than MZ twins in levels of affect and warmth received past their parents,17 a finding that has been replicated by using reports from parents about their own behavior, also equally by observing parents interacting with their different children.18 Studies of adopted children accept also revealed evocative responses in the rearing parents as a part of the child's genetic predispositions, as measured by characteristics in their nascence parents. More coercive parenting and negative affect were reported by the adoptive parents of children born to more than antisocial parents.19 These genetically high risk children displayed more than acquit problems as children and adolescents,20 and thus may have elicited more negative parenting. The key point is that the direction of causality may not necessarily run from parent to kid; when children elicit parental behaviors, information technology tin move in the reverse direction.
Passive rGE effects are best understood in studies comparing parent-kid relationships in adopted and nonadopted children. Since adopted children are not genetically related to their rearing parents, the passive rGE does non influence their similarity, because the parents' genes are non linked to the children's environments. If passive rGE effects arise, whether through cultural manual furnishings or other mechanisms,21 correlations between parenting characteristics and kid outcomes should exist stronger when parents are raising their own genetic children. In fact, one study of adoptive and nonadoptive families plant that parents' ratings of family cohesion, low conflict, and open communication nearly feelings in early babyhood were associated with lower ratings of aggression at historic period seven, but but for nonadopted children.22 This link between early environs and child outcome was not plant for adopted children, suggesting that passive factor-surroundings correlations may exist in nonadoptive families that have increased similarity compared to adoptive families.23
Like other areas of human behavior, parenting itself is subject to genetic influence. This ways that "bad parenting" may itself be influenced by the parents' genetic inheritance. Negative affect, over-control, and even corruption and neglect could be related to the genetic makeup of the parents. This does non mean that environmental factors are unimportant, nor does information technology make such behavior excusable. It just means that genes can explain parenting behavior to some degree.
It is almost certain that parenting has an ecology influence on children. The fact that parental behavior—including parenting style—may exist influenced by genes does non imply that such behaviors take no environmental impact on the children that receive such parenting. What are the best methods for testing the true environmental mediation of the human relationship between parent and child behavior? Behavioral genetic designs—adoption and extended twin studies—actually provide the ideal methods for identifying ecology furnishings while decision-making for genetic factors.24 Behavioral genetic studies accept helped resolve the upshot of genetic and environmental furnishings in abusive parenting and its relationship to later behavior problems in children by studying, for example, differences in the concrete maltreatment of co-twins. Twin resemblance for maltreatment was substantial and equal for MZ pairs and DZ pairs, suggesting that children's genetic differences did not elicit abusive parenting. This does not rule out the possibility, nonetheless, that parents' genes may take influenced their abusive parenting. About importantly, associations between abusive parenting and a child's after antisocial beliefs remained meaning fifty-fifty later controlling for genetic differences in the children.25 It is noteworthy that this genetically informative study provided disarming bear witness of an environmental effect of abusive parenting on child outcomes.
The environmental effects of abuse on child evolution take besides been shown to be exacerbated past a child's genetic predispositions. Children who inherited a deleterious factor that causes a deficiency in monoamine oxidase (MAO-A) appear particularly vulnerable to physical maltreatment, compared to children with a normal MAO-A gene.26 These findings underscore the importance of genotype Ten environment interactions,27 in which genetic predispositions amplify environmental vulnerabilities and vice versa. Nosotros tin can expect that a more detailed understanding of this complex interplay between specific genetic mechanisms and measured environments will emerge over the next few years, every bit more studies brainstorm to obtain Dna markers of genetic variations.
4. Other Family Relationships
Behavioral geneticists accept besides studied family relationships beyond that of the parent and kid. Sibling interactions, for instance, have been examined in both twin and non-twin siblings. Dissimilar parents and children, who always share exactly one-half of their genes, siblings vary in their degree of genetic relatedness. MZ twins are genetically identical; DZ twins and non-twin siblings share about half of their genes, although some pairs may share more or less genetic material. This variation in genetic relatedness could explain why some siblings take a more cooperative and close human relationship than others. Genetic similarity amid siblings has been shown to bear upon both their positive and negative interactions with one another,28 as well equally levels of common competition and cooperation.29 In full general, siblings who share a stronger genetic makeup demonstrate a closer, more cooperative and positive human relationship with ane another.
Genetic variations among siblings living in the same family unit take as well been suggested as an important source of differential parenting. The differential parenting of 2 siblings, albeit stemming originally from their genetic differences, has an ecology effect on the children's psychological outcomes and may amplify sibling differences over time.
The quality of the human relationship between marital partners has too been a subject of behavioral genetic studies. Twin similarity for marital satisfaction has been reported to be greater for MZ pairs than for DZ pairs,30 suggesting the importance of individual genetic factors in determining the success of a marriage. Indeed, twin studies take also shown significantly greater concordance for divorce among MZ pairs than among DZ pairs, suggesting a substantial genetic effect on the likelihood of a failed wedlock.31 Genetically influenced personality traits, such as negative emotionality (i.e., neuroticism), are also predictive of divorce, and may explicate much of the genetic gamble for divorce.32
5. Conclusion
Ane lesson to exist learned from behavioral genetic studies of parenting and other types of family relationships is that one must be conscientious in drawing conclusions based on findings of family resemblance in nuclear, nonadoptive families. Consider the well-known finding that children of abusers are likely to become aggressive and violent, and perhaps even go abusive parents themselves subsequently in life.33 Although it is tempting to assume such resemblance is a office of learning and experience, it is possible that inherited genetic factors could explain the transmission of abuse across generations. Family resemblance for a given characteristic does not necessarily imply either genetic or ecology influence, since either could explain observed similarity amongst family members. Thus, the mere fact that children who are abused by their parents are more than likely to become calumniating themselves does not prove a causal relationship between parenting behaviors and child upshot. Through genetically controlled studies, we take come to understand that both genes and surround play a role in the wheel of violence.34 Genes may predispose certain adults toward violence and aggression, even toward their own children. Such behaviors can in turn accept a real environmental bear upon on the kid'due south mental wellness and on behavioral outcomes. Children's genes may also predispose them toward oppositional and other antisocial behaviors, which may elicit negative parenting from the adults who are raising them.
The fact that genetic influences are crucially important for most areas of beliefs does not mean that environmental influences are unimportant. Genes typically account for no more than than one-half to two-thirds of the variation seen in nearly individual's psychological traits. But most environmental influences are based on private experiences and exposures that are not shared by family members. The implication for families is that most observed resemblance among its private members is a function of their genetic similarity—not their shared experiences.
Finally, behavioral genetic studies of family unit relationships provide the valuable information required to develop effective programs of intervention and prevention of serious mental wellness and behavioral problems. Establishing that environmental effects unequivocally mediate links between parents' and children'due south behavior is a step toward ensuring the success of treatment programs that target either parents or children.
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Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4685725/
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