Over the past several years, much research in the field of Behavior Genetics has gone into discovering how much of your personality is hereditary or learned. What has been discovered is that many of your personality traits appear to have a genetic basis. However, personality is a complex trait, meaning that it is influenced by a variety of different genetic and environmental factors. Furthermore, personality traits are also polygenic, meaning multiple genes are involved in determining a specific trait. Nevertheless, by studying twins and sequencing whole human genomes, scientists have been able to determine specific genetic traits that shape your personality.
Identical twins share the same genotype, so if there is a specific personality trait in which they differ, it is highly unlikely that that trait is genetic in origin. Fraternal twins do not share the same genotype and are no different than siblings of different ages, but they are considered to have more similar environmental effects on personality than traditional siblings. Therefore, a difference in personality between identical twins highlights the effects of their environment, while differences in fraternal twins shed light on a possible genetic cause. Additionally, by sequencing genomes, we are discovering specific genetic markers for certain personality traits. What follows are seven personality traits you wouldn’t think are hereditary, but actually are.
The quest for finding the “smart gene” has been going on for decades. Studies of twins from various socio-economic backgrounds have proven that the environment does not have a prominent effect on IQ; rather, it is hereditary. However, pinning the source down has been problematic.
Researchers have recently discovered that three small mutations, called SNPs, correlated significantly with educational attainment. Seven more SNPs correlated with educational achievement. Unfortunately, between these mutations, the strongest only accounted for just 0.02 percent of the total variation in educational achievement.1
This has led to the theorization that there are potentially thousands of SNPs involved in the shaping of IQ, which correlates to greater learning ability. The hope is that as the cost of whole genome sequencing drops, the missing genes for intelligence may finally be discovered.
We all know this as the Type A personality – high energy, assertive, easily excited and possessing a strong desire to win. What we have recently learned is a variation in the DRD2 dopamine gene is a great predictor of an extroverted personality. Quantitative geneticists have also estimated that the heritability of an extroverted personality is around 40-60%,2 playing a role much bigger than previously thought.
There was a study performed to measure excitement and fear involving a simple video game. Sample Group A from the general public and Group B from the extreme sports community (including a number of BASE jumpers) pressed a button to inflate a virtual balloon. The closer Group A got to popping the balloon, the more fearful they became, registering their highest fear level when the balloon finally did pop. Group B was the opposite. They grew more excited as the balloon filled and took great delight in the popping of the balloon.
What did this study prove? That extreme sports athletes are hard-wired to take huge risks and chances, often with their lives, in the pursuit of thrill. Two of the genes linked to this behavior – HTR2B and NRXN3 – are also, not surprisingly, linked to both violent behavior and addiction.
The Rules of Attraction
We begin life from the splitting of cells, but not every cell division goes perfectly. If so, our left and right sides would be mirror images. Genetic mutations give us our distinctive characteristics, but one thing has been proven: despite all the environmental forces that attempt to shape our rules of attraction, we are all genetically drawn to symmetry.
Both men and women rate symmetrical members of the opposite sex as more attractive and healthier than less symmetrical counterparts.3 This appreciation even found its way into our sense of smell, which explains the entire perfume industry. In one study, hands down, women found the scent of a symmetrical man to be more attractive and desirable, especially if the woman was menstruating.3
While we can’t pare this down to a specific gene, the evidence is clear. We are attracted to genetic symmetry far more than any external, environmental force.
FKBP5 and HTR2A genes are linked to depression. Candidate genes for bipolar disorder include G72/DAOA, DISC1, NRG1, TPH2, BDNF, 5-HTT and DAT1, among others. There are 128 gene variations alone that are associated with schizophrenia, in 108 distinct locations in the human genome.4 Needless to say, hereditary genes play a large factor in behavioral disorders.
Gene therapy is currently used as a treatment for severe forms of behavioral disorders, but these are complex issues with no easy treatment and no cures on the immediate horizon. Fortunately, just because a parent may have a behavioral disorder, it’s not a guarantee that a child will have it. In fact, only 5-10% of children with one parent suffering will schizophrenia will develop schizophrenic symptoms.
Believe it or not, whether you’re easy-going or aggressive is a hereditary factor. Some of the genes related to impulsivity play into this, but perhaps the biggest genetic player in the biological aspect of your self-control is the MAOA gene.
Men who commit extreme acts of violence often have a high-functioning or low-functioning version of the MAOA gene. Studies have also shown that nearly half of the individual variation in aggressiveness is inherited.5 It may go even further back than that, as anthropologists who, several decades ago, lived with exceptionally violent hunter-gatherers found that those hunter-gatherers who committed the most acts of violence also had the most children, as they were more likely to survive and procreate, putting merit into the argument that violence is not only part of our genetic makeup, it’s also part of our deep ancestral past.5
Openness to experience
Some people prefer to travel; some people prefer to stay at home. This was often thought of as being a product of your environment, but studies show it may have more to do with hereditary factors than we originally thought. The primary method of proof for this theory is, once again, twin studies, where the genetic influence was found to be substantial while there was little evidence of the shared living environment in affecting openness and conscientiousness.
Possessing, or not possessing, this trait can have a profound influence in how you view the world. It may affect how you interact with strangers, where you live and even whom you vote for at election time. Right now, however, there is no genetic smoking gun. More work needs to be done to find specific gene or mutation links.
Stacy Matthews Branch is a writer for Macrogen Corporation, a NGS clinical services company. Stacy is a U.S.-educated biomedical research scientist, toxicologist, medical writer, veterinary medical doctor, and fellow of the American College of Forensic Examiners, with over 20 years of practical professional experience (academia, government, private sector).
Genetics, Personality, and You