To What Extent Do Genes Affect Behavior?
You know that joke that you’re destined to turn into your mother, both the good and the bad, even though you insist that you’ll never be like that? How many times has a parent done something annoying and you swear to yourself that you’ll never be like that to your children, yet sure enough, you start to see signs of this behavior in yourself? There’s some scientific truth behind the idea that you’ll inherit traits (the good, the bad, and the ugly) from your parents, but you’re probably familiar with the nature versus nurture debate as well, which raises the question: to what extent are our personalities products of our genetic makeup?
The theory of evolution teaches us that our species thrives and evolves by passing on only the fittest, or best-adapted genes, to future generations. Natural selection, a key mechanism of evolution, is the variation of the survival and reproduction patterns of individuals over time due to differences in phenotype. Charles Darwin, the “father of evolution,” ruled that only the fittest, most well-adapted organisms will survive; those less adapted for survival will become extinct, leaving only the best-adapted organisms to repopulate. But this is all textbook stuff. You learned all this in high school biology.
Based on the theory of evolution, one would be inclined to think that genes play a large part in influencing our personalities. Have a short temper? Worry a lot? Bit of a pushover? Blame it on your genes, right? Well…maybe not as much as we’d like to think. Ultimately, scientists still don’t know, definitively, what percent of our personalities are shaped by genes, but that’s not from lack of trying. Scientists have spent billions of dollars on genetic research, specifically behavioral genetics, and while they have discovered links between some behavioral disorders and genetics, it should be noted that behavioral genetics is extremely difficult to study because the genetic factors leading to certain behaviors in individuals must be separated from environmental factors.
Case in point for the complicated nature of behavioral genetics: scientists have studied the genetic differences between fraternal and identical twins and found that heritability (i.e. the amount of variation in personality that can be explained by genes) is roughly 46% for identical twins and 23% for fraternal twins. This research is promising, in that it implies a definite correlation between personality and genes. However, studying which genes, among the more than 50,000 gene pairs in the human genome, are responsible for personality traits is where things get a little messy.
“Gene for” studies, aptly named for the study of finding genes for various personality traits, is a an exciting and potentially groundbreaking field of scientific study; however, as exciting as this research can be, it can prove equally frustrating. Just by studying the rates at which certain behavioral disorders are passed down within families, scientists have been able to confirm genetic links between schizophrenia, alcoholism, obesity, and depression. Furthermore, scientists have studied the relation of repeating sections of genes, known as single nucleotide polymorphisms (SNPs) to the production or reception of neuropeptides implicated in various social behaviors in non-human species. By studying these gene sequences in animals, researchers have found SNPs related to an increased risk for Alzheimer’s Disease in humans and increased oxytocin receptors in the brain. These studies are promising because if we can target the specific parts of personality that neuropeptides influence, then we should be able to predict behavioral patterns based on genetic variants. But (yes, there’s a but) unfortunately there’s still a long way to go when it comes to linking specific SNPs to personality traits, because for every SNP linked to a personality characteristic, there was a null reception. Many of the most promising genes linked to behavioral traits, such as the MAOA gene attributed to antisocial behavior, have failed to replicate in subsequent studies.
So, if you were hoping for an answer to the question I posed at the beginning of this article, I’m sorry to disappoint, but research is simply not there yet in finding a definite genetic link to personality. Research have been able to link some personality traits to SNPs, but the studies are contradictory. For now, the nature versus nurture debate continues.