If you have ever wondered why your sibling is outgoing while you would rather stay home — or vice versa — you've probably considered the possibility a genetic influence is at work.

Personality is complicated, and so are the basic components that make up an organism's genetic code: genes and DNA. Genes are the specific segments of DNA that carry instructions for producing proteins and determining various traits in an organism.

Now researchers have undertaken one of the largest studies ever to investigate the genetic roots behind the ways people think, feel and behave.

The findings do not serve as a genetic fortune-telling device. Instead, they offer something potentially more useful.

The study identified more than 1,260 genetic variants associated with the five broad personality traits known as the Big Five:

  • Extroversion
  • Agreeableness
  • Conscientiousness
  • Neuroticism (a tendency toward anxiety, depression and self-doubt)
  • Openness to experience

An international team of researchers, the Revived Genomics of Personality Consortium, combined genetic and personality data from 46 research cohorts. Their analysis included between 611,037 and 1.14 million participants, depending on the trait being examined. Participants represented both European-like and African-like genomes.

Participants provided their DNA samples and completed validated questionnaires measuring the Big Five traits. Researchers then conducted genome-wide association analyses. They scanned roughly 10 million genetic variants to identify DNA differences associated with personality. They also used within-family analysis involving relatives to investigate whether apparent genetic associations might reflect shared family environments instead.

The large scale of the study allowed researchers to find far more personality-related genetic variants than earlier work had. Of the 1,260 variants identified, 824 had not previously been associated with personality. For instance, extroversion was linked to 258 variants, while neuroticism was connected to 706. The study also identified 131 variants for conscientiousness, 39 for agreeableness and 126 for openness. Still, despite its wide range, the findings do not mean that DNA determines who someone will become. The common genetic variants identified only a modest share of differences in personality.

Researchers scanned roughly 10 million genetic variants to identify DNA differences associated with personality. They also did a within-family analysis of relatives to account for the effects of shared family environments.

The team emphasized that environmental influences remain important. "There is no single "personality gene," lead author Ted Schwaba, an assistant professor in the Department of Psychology at Michigan State University, said in a press release. "Personality traits are associated with many genetic variants, but even the largest effects of individual genetic variants are still very small. However, even though any individual genetic variant makes very little difference in personality, the effects of many variants together can be more sizable."

The researchers also looked beyond personality itself and into the behaviors that appear to be associated with the different genetic profiles they studied. For instance, genetic patterns associated with conscientiousness were linked with behaviors such as greater daytime activity, healthier eating and better sleep. Variants associated with neuroticism were more frequent with psychiatric disorders, higher body mass index and smoking.

Genetic patterns related to extroversion were associated with a lower risk of some internalizing disorders, including anxiety and depression and ADHD or attention-deficit/hyperactivity disorder.

Life experiences and environment remain part of the equation, interacting with thousands of genetic influences over a lifetime and helping shape who someone ultimately becomes.

The study also noted associations with broader life outcomes including education, career paths, income, health, longevity, residential mobility and time spent in hospitals. Importantly, these are genetic associations, not proof that a particular variant directly causes a particular outcome.

The findings do not serve as a genetic fortune-telling device. Instead, they offer something potentially more useful: evidence that personality is influenced by an intricate network of genetic factors, each exerting a small effect within a much larger human story.

The practical takeaway is less about predicting an individual's personality than understanding its complexity. A genetic tendency toward a trait does not dictate a person's choices, relationships or health. Life experiences and environment remain part of the equation, interacting with thousands of genetic influences over a lifetime and helping shape who someone ultimately becomes.

The study is published in the journal Nature.