Genetics is the study of genes and the variation of characteristics that are influenced by genes—including physical and psychological characteristics. All human traits, from one's height to one's fear of heights , are driven by a complex interplay between the expression of inherited genes and feedback from the environment .
Scientists are tasked with a massive but increasingly plausible mission: mapping the pathway from one's genes to the person one sees in the mirror. What they learn about the power of genes has implications for understanding mental illness and psychological differences between individuals, as well as the psychological effects of non-genetic factors.
Key Takeaways
- Genetics affects mental, emotional, and physical wellbeing
- Understanding genetics is the first step toward managing it
- Evidence-based approaches can significantly improve outcomes
- Building daily habits is more effective than one-time interventions
Why Genes Matter in Psychology
Genes help to define who an individual is inside and out. While non-genetic factors have a role to play, too, what scientists have learned about these influences can clash with common wisdom . A characteristic or behavior that appears to result from a child’s upbringing—such as a proneness to mental illness or divorce — may actually be largely a product of the genes she inherited from her parents. In fact, research investigating the influence of the family environment suggests that it accounts for a surprisingly small amount of the difference between people on characteristics that scientists measure.
A gene is the basic unit through which genetic information is stored and passed between generations. Physically, a gene is a specific section of one of the long, double-helix-shaped DNA molecules that appear in each cell of the body. Genes vary in size, comprising anywhere from hundreds to millions of the nucleotides that collectively make up DNA. Many (but not all) genes provide chemical “instructions” for the creation of protein molecules, or serve other roles that are integral to the function of an organism. Different versions of the same gene are called alleles.
The genome is the entirety of the genetic material contained in an individual. Human DNA is estimated to contain between 20,000 and 25,000 genes. The vast majority of each person’s genome is identical to that of the next person, but the portion that differs is consequential for how individuals develop.
A chromosome is a structure within a cell nucleus that is made up of a long DNA molecule and proteins that provide support. Each human cell contains 23 pairs of chromosomes, which together store a person’s genetic code.
In addition to visible traits like weight and eye color, psychological qualities such as personality traits (such as extraversion and agreeableness ), intelligence , risk of mental illness, and many others are to some extent influenced by genetics. While genes do not account for all of the differences between people on these characteristics, research indicates that they have a substantial impact.
People’s levels of risk for all major psychiatric disorders are determined partly by genetics. Estimates of how much variability in risk can be attributed to genetic differences between individuals include: 75 percent or more for ADHD , autism spectrum disorders, bipolar disorder , and schizophrenia; 50 to 60 percent for alcohol dependence and anorexia nervosa, and 20-45 percent for anxiety disorders, OCD , PTSD , and major depressive disorder.
The Science of Genetics and Behavior
It may seem obvious that the genes people inherit from their parents and share with their siblings have an effect on behavior and temperament. Individuals are often noticeably more similar in a variety of ways to immediate family members than they are to more distant ones, or to non-relatives. Of course, there are plenty of notable differences within families as well. Scientists have employed an array of methods to drill down into how and to what extent genetic differences truly account for psychological differences.
Behavioral genetics, or behavior genetics, is the study of psychological differences between individuals and how genetic and non-genetic factors create those differences. Among other questions, behavioral genetics researchers have sought to determine the extent to which various specific differences in people’s behaviors and traits can be explained by differences in their genetic code.
Scientists use specialized methods to explore the links between genes and individual differences. Studies of twins who either do or do not have identical genomes allow for estimates of the degree to which genes drive the variation in psychological traits. Other methods, such as studying adopted children and their adoptive and biological parents, have been used as well. In recent years, genome-wide association studies (GWAS) have emerged as a major approach in behavioral genetics. A GWAS uses genetic testing to identify numerous genetic differences across many individuals , then analyze the association between these differences and personality traits or other outcomes.
Heritability is a measure of how much of the differences between people on a given characteristic can be attributed to genetics. More specifically, it is an estimate of the amount of variation between individuals in a given population that can be accounted for by genetic differences. Behavioral genetics research indicates that every trait is (at least) a little bit heritable —though the fact that a trait is heritable does not mean it is fixed.
Heritability estimates range from 0 to 1, or from zero percent to 100 percent. For example, if the heritability of a trait is estimated to be 50 percent, that suggests that about half of the overall variation between different people on measures of that trait—within the specific group of people measured—is due to differences in their DNA. (If heritability of a trait was 100 percent, identical twins , who share the same genetic code, would be exactly the same on that trait—but that doesn’t actually happen.)
Genes and the environment do not work completely independently. In what scientists call gene-environment interaction, aspects of the environment may have different effects on an individual depending on her genetic code. For example, adverse childhood experiences may have a severe impact on someone with a certain genetic disposition and a less-severe effect on someone with different genes. Gene-environment interaction can also work the other way around: the influence of genes on an outcome may depend on a person’s environment.
Frequently Asked Questions
What exactly is genetics?
Genetics is the study of genes and the variation of characteristics that are influenced by genes—including physical and psychological characteristics. All human traits, from one's height to one's fear of heights , are driven by a complex interplay between the expression of inherited genes and feedback from the environment .
Is genetics a serious condition?
Genetics exists on a spectrum. While mild forms are a normal part of life, persistent or severe genetics can significantly impact daily functioning and quality of life. It's important to seek professional support if genetics is interfering with work, relationships, or wellbeing.
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