10 A Framework for Thinking About Heritability and Class
Genes play an important role in human behavior and social class, though this is not always accepted in schools. Some sociologists believe class is mostly about social issues like privilege and oppression, while many psychologists accept that heredity matters. Francis Galton was one of the first to study heritability and found that related people often succeed in similar areas. Research methods, such as studying identical and fraternal twins, help scientists understand how much traits come from genes versus the environment. Heritability measures the genetic influence on traits.
Heritability
Heritability is a scientific term used to explain how much of the differences in a trait, like height or intelligence, within a population can be linked to genetics. While most people can see that children often look like their parents, heritability is more complicated and is calculated as the ratio of genetic variation to total variation in a trait. There are two types of heritability: broad heritability (H2) which includes all genetic influences and narrow heritability (h2) which focuses only on additive genetic effects.
Additive variation happens when a trait results from simply adding the effects of alleles from both parents. For example, if one allele causes a red flower color and another causes white, the resulting flower color can be a mix based on which alleles are present. Nonadditive variation occurs when gene interactions change how traits are expressed. This includes epistasis, where one gene can affect the expression of another, and dominance, where one allele can hide the effects of another. Additive variation is usually the main focus because it’s the most straightforward way to measure heritability, though nonadditive influences are considered when expected results don’t match.
There are common misunderstandings about heritability. It refers to populations, not individuals. For instance, if genetics explain 70% of the height differences in a population, it doesn’t mean that genetics explain 70% of one person’s height. Heritability can also change depending on age and the specific group being studied. For example, heritability of traits, such as IQ, often increases as people grow older. Additionally, heritability can differ from one population to another due to environmental factors, like how much access people have to education.
Heritability can increase as society improves. If more people have access to good education, the heritability of educational achievement may also rise because when everyone has similar opportunities, the impact of the environment becomes less important. This was seen in Norway, where better access to education from the 1960s to the 2000s led to higher heritability of education levels.
To calculate narrow heritability, researchers use a model called the ACE model, which divides total variability into three parts: additive genetic variance (A), shared environmental variance (C), and nonshared environmental variance (E). Twin studies are particularly useful because they compare monozygotic (MZ) twins, who share nearly all their genes, with dizygotic (DZ) twins, who share about half. This approach helps researchers understand how much genetics and environment contribute to traits. Studies of twins, especially those raised apart, have shown the important role of genetics in shaping traits, highlighting the complex relationship between biology and environment in our development.
The Validity of Twin Studies
The ACE model in twin studies aims to separate the influences of genetics (nature) and environment (nurture). However, it relies on two key assumptions that have faced criticism. First is the random mating assumption, which states that parents mate without regard to traits like height. If this assumption is wrong and people tend to marry others with similar traits, it can inflate estimates of the shared environment and underestimate genetic contribution. Research shows that assortative mating is common across many traits.
The second assumption is the equal environments assumption (EEA), suggesting that identical twins (MZ) share more similar environments than fraternal twins (DZ). Some studies indicate this may not significantly affect the outcomes of studies in areas like intelligence and mental health, meaning the impact of this assumption is likely small. Overall, while there are criticisms of twin studies, the evidence suggests these studies tend to slightly underestimate genetic influence rather than overstate it.
Recapitulation
To understand why some people achieve financial and professional success while others do not, it's important to consider both genetic and environmental factors. It is challenging to separate these influences with usual studies. However, studying identical (MZ) and fraternal (DZ) twins has provided valuable insights. By comparing these twins, researchers can analyze how much genes and shared family environments impact success. This method has led to thousands of studies that reveal important findings about these influences.
Genes play an important role in human behavior and social class, though this is not always accepted in schools. Some sociologists believe class is mostly about social issues like privilege and oppression, while many psychologists accept that heredity matters. Francis Galton was one of the first to study heritability and found that related people often succeed in similar areas. Research methods, such as studying identical and fraternal twins, help scientists understand how much traits come from genes versus the environment. Heritability measures the genetic influence on traits.
Heritability
Heritability is a scientific term used to explain how much of the differences in a trait, like height or intelligence, within a population can be linked to genetics. While most people can see that children often look like their parents, heritability is more complicated and is calculated as the ratio of genetic variation to total variation in a trait. There are two types of heritability: broad heritability (H2) which includes all genetic influences and narrow heritability (h2) which focuses only on additive genetic effects.
Additive variation happens when a trait results from simply adding the effects of alleles from both parents. For example, if one allele causes a red flower color and another causes white, the resulting flower color can be a mix based on which alleles are present. Nonadditive variation occurs when gene interactions change how traits are expressed. This includes epistasis, where one gene can affect the expression of another, and dominance, where one allele can hide the effects of another. Additive variation is usually the main focus because it’s the most straightforward way to measure heritability, though nonadditive influences are considered when expected results don’t match.
There are common misunderstandings about heritability. It refers to populations, not individuals. For instance, if genetics explain 70% of the height differences in a population, it doesn’t mean that genetics explain 70% of one person’s height. Heritability can also change depending on age and the specific group being studied. For example, heritability of traits, such as IQ, often increases as people grow older. Additionally, heritability can differ from one population to another due to environmental factors, like how much access people have to education.
Heritability can increase as society improves. If more people have access to good education, the heritability of educational achievement may also rise because when everyone has similar opportunities, the impact of the environment becomes less important. This was seen in Norway, where better access to education from the 1960s to the 2000s led to higher heritability of education levels.
To calculate narrow heritability, researchers use a model called the ACE model, which divides total variability into three parts: additive genetic variance (A), shared environmental variance (C), and nonshared environmental variance (E). Twin studies are particularly useful because they compare monozygotic (MZ) twins, who share nearly all their genes, with dizygotic (DZ) twins, who share about half. This approach helps researchers understand how much genetics and environment contribute to traits. Studies of twins, especially those raised apart, have shown the important role of genetics in shaping traits, highlighting the complex relationship between biology and environment in our development.
The Validity of Twin Studies
The ACE model in twin studies aims to separate the influences of genetics (nature) and environment (nurture). However, it relies on two key assumptions that have faced criticism. First is the random mating assumption, which states that parents mate without regard to traits like height. If this assumption is wrong and people tend to marry others with similar traits, it can inflate estimates of the shared environment and underestimate genetic contribution. Research shows that assortative mating is common across many traits.
The second assumption is the equal environments assumption (EEA), suggesting that identical twins (MZ) share more similar environments than fraternal twins (DZ). Some studies indicate this may not significantly affect the outcomes of studies in areas like intelligence and mental health, meaning the impact of this assumption is likely small. Overall, while there are criticisms of twin studies, the evidence suggests these studies tend to slightly underestimate genetic influence rather than overstate it.
Recapitulation
To understand why some people achieve financial and professional success while others do not, it's important to consider both genetic and environmental factors. It is challenging to separate these influences with usual studies. However, studying identical (MZ) and fraternal (DZ) twins has provided valuable insights. By comparing these twins, researchers can analyze how much genes and shared family environments impact success. This method has led to thousands of studies that reveal important findings about these influences.