The question of whether our genes influence our personality essentially boils down to nature versus nurture, one of the oldest debates in the history of psychology. It has dominated personality theory since Darwin noticed that survival meant passing on the most capable of our genes to the next generation.

On the one side, there's the notion that the apple doesn't fall far from the tree ("nature"). Children inherit eye color, skin pigmentation and vulnerability to specific illnesses from one or other parent, and they inherit specific personality traits in the same way. Personality is wired in, and no quirks of upbringing will change it.

In the opposing corner stands the theory of nurture. Nurture argues that the human mind is a blank slate, and it's the sum total of your environment, learning and experiences that shape you to be the person you are today.

So, who's wrong? Who's right? Let's take a closer look.

Nature Versus Nurture in Psychology

The nature versus nurture debate is an on-going one and one that reflects the popular culture of the time. Back in Darwin's day, for example, the psychologist and eugenicist Francis Galton (himself a cousin of Charles Darwin) was convinced that intelligence was hereditary and that society could be improved through "better breeding."

Freud changed the popular thinking. He believed that personality was shaped by conflicts resolved in childhood and how an individual learned to navigate their physical environment. Throughout much of the 20th century, this behaviorist or nurture approach dominated psychology. It was commonly believed that human personality was primarily influenced by their environment and could be changed through social conditioning. It was during this time that Bandura conducted his famous Bobo doll experiment to show that aggression could be learned through imitation and thousands of Americans hit the psychotherapy couch to talk about their childhood.

Today, research into the human genome has given scientists a much better understanding of how traits and certain behavioral characteristics are passed from parent to child. Recent research on twins reveals that genetics have a stronger influence on the development of certain personality traits than previously thought, and may even play a larger role than child rearing.

The Twin Studies

For 20 years, researchers at the University of Minnesota studied 350 pairs of twins, some of whom were raised in different families. The landmark study was the first of its kind to compare twins raised independently with those raised in the same environment. This allowed researchers to assess the relative influence of heredity and of upbringing in their development.

During the study, participants were put through a series of personality tests which broadly followed the Big 5 personality test. Big 5 measures test-takers against five core personality traits, as well as various sub-traits. These are:

O - Openness to experience (your level of curiosity)

C - Conscientiousness (your level of work ethic)

E - Extraversion (your level of sociability)

A - Agreeableness (your level of kindness)

N - Neuroticism (your level of anxiety or shame).

The results are fascinating. For most of the traits measured, more than half the variation between the twins was shown to be genetic. Among the traits found most strongly determined by heredity were ambition, vulnerability to stress (neuroticism), leadership, risk-seeking, a sense of well-being and, surprisingly, respect for authority. The genetic factor for these traits was found to run somewhere in the region of 50 to 60 percent.

Jim Lewis and Jim Springer, the most astounding raised-apart twin set in the Minnesota study, were shown to be so similar in the personality variables of tolerance, flexibility and conformity that it was almost impossible to tell them apart.

Do Parents Still Matter?

Even though the twin studies demonstrate the strong influence of nature, family influence still matters. More recent studies, for example, have shown that the personality trait of conscientiousness has a far lower genetic correlation than the other personality traits. This suggests that a parent or educator might equip an inherently spontaneous child with the tools she needs to show duty and self-discipline, and thus influence the development of her personality.

It's not just family influence that matters, either. In a recent British study, researchers found that, on average, 60 percent of the variation in a child's unruly behavior in school was down to their genes. But in London and other global hotspots, environment played a far greater role. The researchers concluded that issues such as deprivation, housing, education and even pollution levels could all influence how your DNA expresses itself as personality.

This brings us to another fascinating conclusion drawn by the Minnesota twin studies. Researchers found that raised-apart identical twins are more similar than identical twins that are raised together. That's because together-twins have the opportunity to recognize their similarities and deliberately change their behavior so they might be different from their sibling - effectively turning off their genes.

All of which seems to suggest that, even if we do inherit certain parts of our personalities, we're not forever stuck with them. There's a strong possibility that we can change our disposition simply by changing our environment, or possibly even through sheer force of will.

Summing It Up

The current thinking is pretty clear - our personalities are shaped by biology and upbringing, and it is almost impossible to hold an all-or-nothing view. Instead of asking whether personality is down to nature or nurture, the question should be, how much? How much of our personalities is down to nature and how much can we control and change over time? And can we even put a figure on something that has so many variables?

So if you're looking at your child and thinking, "Where did that personality come from?" the answer is, at least a little bit from you. But with multiple personality dimensions to look at, and two parents, this won't result in an exact type match very often. Our personality type code is shorthand for a hugely complex system of thought processing. Until we can map the specific genetic code for each individual personality trait, we're going to have to embrace the mystery of our personalities and how our own unique character came to be.

Molly Owens
Molly Owens is the founder and CEO of Truity. She is a graduate of UC Berkeley and holds a master's degree in counseling psychology. She began working with personality assessments in 2006, and in 2012 founded Truity with the goal of making robust, scientifically validated assessments more accessible and user-friendly. Molly is an ENTP and lives in the San Francisco Bay Area, where she enjoys elaborate cooking projects, murder mysteries, and exploring with her husband and son.