We all have a friend like this — one with an extra pep in her step who is always smiling and laughing, and who is the eternal optimist. This friend appears to be happier than the rest of us, and even predisposed to “walk on sunshine.” Now, in a recent study, scientists have identified happiness may be in the genes. Specifically, their study found that how happy a person feels about his or her life can be influenced by the changes in DNA that make each of us unique.

"This study is both a milestone and a new beginning: A milestone because we are now certain that there is a genetic aspect to happiness and a new beginning because the three variants that we know are involved account for only a small fraction of the differences between human beings,” said Meike Bartels, a professor of Genetics and WellBeing at VU Amsterdam, in a statement.

Bartels, along with a group of nearly 200 scientists in 17 countries, examined common DNA variations in more than 300,000 different individuals to analyze phenotypes — observable traits resulting from interactions between genes and environment. Their research explored subjective well-being (how happy a person thinks or feels about his or her life), depressive symptoms, and neuroticism. The project factored in mental health issues, and also five physical risk factors for adverse health outcomes that may affect a person's mood: body mass index (BMI), smoking status, coronary artery disease, fasting glucose levels and triglyceride levels.

The findings revealed subjective well-being, neuroticism and depression are predominantly influenced by the same set of genes. Three genetic variants are linked to happiness, which is mainly expressed in the central nervous system, adrenal glands, and pancreatic system. Just two genetic variants can explain depression, and 11 are linked with neuroticism. The genetic variants identified only account for a small percentage of these genetic associations.

Researchers also noted genes expressed in tissues that play a key role in hormone production were also affecting traits associated with well-being. This is in addition to genes that are expressed in the central nervous system.

“Hormones clearly have an important influence on the regulation of mood and stress,” said Professor Elina Hypponen, senior author, center director for Population Health Research at the University of South Australia and a principal fellow at the SA Health and Medical Research Institute (SAHMRI), in a statement.

The researchers also observed whether the genetic variants they identified overlapped with genetic variants associated with other diseases and disorders, including Alzheimer’s, anxiety, autism spectrum disorder, bipolar disorder and schizophrenia. The strongest link proved to be with anxiety disorders, while the genetic variants tied to subjective well-being, depression, and neuroticism moderately overlapped with the variants linked to schizophrenia and bipolar disorder.

So what exactly drives happiness?

“Genetics is only one factor that influences these psychological traits. The environment is at least as important, and it interacts with the genetic effects,” said Daniel Benjamin, corresponding author and associate professor of the Center for Economic and Social Research at the University of Southern California Dornsife College of Letters, Arts and Sciences, in a statement.

This suggests psychological well-being is influenced by both genes and environment. The researchers hope locating these variants will allow them to better study the interaction between nature and nurture, as the environment is responsible for the differences in the way people experience happiness — to a certain extent.

Previous studies suggest genes account for about half of what makes people happy, or whether they are sociable, active, stable, hardworking, or conscientious. In a 2008 study, researchers at the University of Edinburgh observed happiness levels and personality traits in more than 900 twin pairs. The findings showed identical twins shared more personality traits than a pair of non-identical twins, and when asked how happy they were, the identical pair responded more similarly. This suggests happiness and personality have a strong genetic component.

However, these genes won’t guarantee happiness because this is also contingent on a variety of external factors, such as relationships, health, and careers.

There is a plethora of evidence on the influence of genes’ on happiness, but it’s important to remember there are many genes involved, and thousands of DNA variants for complex traits. So, there isn’t a gene for happiness, but there are many genes and these interact with our environmental experiences, which is what ultimately influences our happiness levels.

We can still change our outlook — even if we’re predisposed to be unhappy.

Source: Okbay A, Baselmans BML, De Neve JE et al. Genetic variants associated with subjective well-being, depressive symptoms, and neuroticism identified through genome-wide analyses. Nature Genetics. 2016.