11 The Ubiquity of Heritability and the Small Role of the Shared Environment
The Unexpected Story of the Shared Environment
Research over the past few decades has shown that while genetics plays a big role in human behavior, the family environment has a smaller impact than many people think. Eric Turkheimer described three key laws of behavior genetics. The first law states that all human traits have some genetic link. The second law explains that being raised in the same family has less influence on behavior than genes do. The third law highlights that a large part of the differences in behaviors cannot be explained by genetics or family life.
Studies by John Loehlin and Robert Nichols found that twins raised together often have different personalities, leading to the idea of the nonshared environment. This means that differences between siblings raised in the same household happen randomly and are not strongly linked to family influences.
While poor parenting can cause serious harm, especially in cases of neglect or abuse, socioeconomic status does affect life outcomes, mainly in terms of money. However, it has a limited effect on children's personalities and abilities. Family wealth can help children in certain careers, particularly in politics, but it usually does not have much impact in competitive jobs that require higher skills.
The Polderman Meta-Analysis of Twin Studies
A large study was done by a team of researchers from different countries to look at twin studies that had been published over many years. They focused on the idea of heritability, which tells us how much our traits are influenced by genetics compared to the environment. The researchers examined data from about 14 million twin pairs across many traits, using a method called the ACE model that takes into account genetic factors, shared environmental effects, and nonshared environmental effects.
They found that the ACE model often applies well, showing that genetic factors usually explain a lot of the differences in traits between identical twins and fraternal twins. In many cases, the effects of the shared environment were very low or even nonexistent, which means traits were mostly influenced by genetics rather than the environment they shared. When the model suggested that shared environmental effects were negative, it indicated that the heritability of traits might be underestimated.
The results were divided into three main areas: personality traits, cognitive abilities, and social behaviors. For personality traits, the study showed that genetics play a big role, while the shared environment had a minimal impact. Looking at cognitive abilities, traits such as memory and attention also showed strong genetic influences. In terms of social behaviors, things like relationships and work dynamics were mostly influenced by each individual's unique experiences rather than by family background.
The study also looked at psychological disorders. It found that while parents can affect their children's behavior, severe mental disorders are more influenced by genetics than by parenting. When it came to intelligence, the researchers showed that the impact of the shared environment was greatest in early childhood but dropped significantly as children grew older, becoming almost nonexistent by adolescence.
Finally, when examining personality characteristics, the study found that the shared environment had almost no effect, meaning that people's differences in personality are largely due to genetics and their unique individual experiences. Overall, the study emphasizes that genetics are very important in shaping who we are, while the shared environment has a much smaller influence than previously thought.
Recapitulation
Studies show that a family's socio-economic status (SES), which includes things like income and education, doesn't really explain the cognitive abilities and personality traits that parents try to develop in their children. This finding might surprise many parents and is backed by strong evidence. However, it doesn’t mean SES isn't important for understanding differences among families. An example from the past highlights how just seeing a link between two things does not mean one causes the other, which indicates that more research is needed on how SES affects inherited traits.
The Unexpected Story of the Shared Environment
Research over the past few decades has shown that while genetics plays a big role in human behavior, the family environment has a smaller impact than many people think. Eric Turkheimer described three key laws of behavior genetics. The first law states that all human traits have some genetic link. The second law explains that being raised in the same family has less influence on behavior than genes do. The third law highlights that a large part of the differences in behaviors cannot be explained by genetics or family life.
Studies by John Loehlin and Robert Nichols found that twins raised together often have different personalities, leading to the idea of the nonshared environment. This means that differences between siblings raised in the same household happen randomly and are not strongly linked to family influences.
While poor parenting can cause serious harm, especially in cases of neglect or abuse, socioeconomic status does affect life outcomes, mainly in terms of money. However, it has a limited effect on children's personalities and abilities. Family wealth can help children in certain careers, particularly in politics, but it usually does not have much impact in competitive jobs that require higher skills.
The Polderman Meta-Analysis of Twin Studies
A large study was done by a team of researchers from different countries to look at twin studies that had been published over many years. They focused on the idea of heritability, which tells us how much our traits are influenced by genetics compared to the environment. The researchers examined data from about 14 million twin pairs across many traits, using a method called the ACE model that takes into account genetic factors, shared environmental effects, and nonshared environmental effects.
They found that the ACE model often applies well, showing that genetic factors usually explain a lot of the differences in traits between identical twins and fraternal twins. In many cases, the effects of the shared environment were very low or even nonexistent, which means traits were mostly influenced by genetics rather than the environment they shared. When the model suggested that shared environmental effects were negative, it indicated that the heritability of traits might be underestimated.
The results were divided into three main areas: personality traits, cognitive abilities, and social behaviors. For personality traits, the study showed that genetics play a big role, while the shared environment had a minimal impact. Looking at cognitive abilities, traits such as memory and attention also showed strong genetic influences. In terms of social behaviors, things like relationships and work dynamics were mostly influenced by each individual's unique experiences rather than by family background.
The study also looked at psychological disorders. It found that while parents can affect their children's behavior, severe mental disorders are more influenced by genetics than by parenting. When it came to intelligence, the researchers showed that the impact of the shared environment was greatest in early childhood but dropped significantly as children grew older, becoming almost nonexistent by adolescence.
Finally, when examining personality characteristics, the study found that the shared environment had almost no effect, meaning that people's differences in personality are largely due to genetics and their unique individual experiences. Overall, the study emphasizes that genetics are very important in shaping who we are, while the shared environment has a much smaller influence than previously thought.
Recapitulation
Studies show that a family's socio-economic status (SES), which includes things like income and education, doesn't really explain the cognitive abilities and personality traits that parents try to develop in their children. This finding might surprise many parents and is backed by strong evidence. However, it doesn’t mean SES isn't important for understanding differences among families. An example from the past highlights how just seeing a link between two things does not mean one causes the other, which indicates that more research is needed on how SES affects inherited traits.