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Key points
- Everything about us is partly genetic, but this doesn’t mean genes determine our traits.
- Our genes assemble every aspect of our partly unique organisms, including our brains.
- We develop unique personalities as we try to thrive with our organisms’ peculiarities, given our environments.
Behavioral geneticists study the genetic and environmental underpinnings of psychological and many other human traits. With a decades-long history and well-established research methods, the field has produced some of the most well-replicated findings in psychology. But not everyone likes the findings. I think this is mainly because of misunderstanding what these results mean.
The First Law: Everything is Partly Heritable
Eric Turkheimer has coined behavioral genetics’ three most fundamental laws. The first law is: "All human behavioral traits are [partly] heritable.”
This law is based on the statistical trend for genetically similar people—identical twins, but also ordinary siblings or parents and children—to be similar in almost any measurable trait, including personality traits. Of course, this trend is just a statistical abstraction, only being true “on average” and among sufficiently large samples. Individual people like you and me are only slightly more likely to resemble our parents or siblings than any random stranger.
This trend has been replicated so many times for so many traits that no credible researcher will dispute it. What is being debated, however, is how to think about it.
A Commonsensical Interpretation
I don’t think there has to be anything controversial about genetically more similar people tending to be more similar psychologically—that is, in terms of their personality traits.
It would be weird if my genes had no relevance to how I typically behave, think, and feel. They dictate the production of every protein making up every part of my organism, including my brain. To survive and thrive, I have to continually match the quirks of this organism and its brain to the available circumstances. In doing so, I behave, think, and feel in certain ways, which makes up my unique personality.
For some basic examples, I am constantly developing habits to make the best of not being very tall and strong, not having the best eyesight or most handsome face, yet having efficient metabolism, good stamina, and not needing much sleep. There are countless other peculiarities about my body and brain that I can work around or capitalize on to develop behavior, thinking, and feeling patterns that best fit me with the circumstances available to me.
The same is true for any other person. Unless people are identical twins, their genetic make-ups are slightly different; hence their organisms, including their brains, are somewhat different (even identical twins’ are, in fact). To thrive with the quirks of their organisms and brains, they often have to behave, think and feel differently. Hence, their personalities are slightly different.
The more people differ genetically, the more unique their organisms and brains are, and the more likely they are to rely on different patterns of behavior, thinking, and feeling to find the snuggest possible fits with the circumstances available to them.
All of this sounds commonsensical to me: People’s genetic variations mean that the proteins that make up their organisms are assembled somewhat differently, and to thrive with their unique organisms, they develop different patterns of behaving, thinking, and feeling.
How This Is Often Misinterpreted
It gets messy if we wrongly interpret psychological similarity among genetically related people as evidence for genetic determinism.
It is not uncommon to assume this statistical trend to mean that there must be specific genes for certain traits, making us somehow hardwired for our traits. And of course, many find this conclusion controversial.
But there is no evidence for any of this. For example, although people’s different extraversion levels are partly due to their genetic differences, we know of no genes specifically responsible for extraversion—or any other personality trait, for that matter. Likewise, it is common for people’s personality trait levels to change, either spontaneously, as a result of their experiences, or even because they deliberately want to change.
The most obvious reason that genes do not fix people’s psychological destinies is that genetically similar people's traits only resemble on average, and even genetically identical individuals are often very different.
But even to the extent that genes do play a role, large studies have clearly shown that people’s differences in any psychological trait can be linked with many thousands of little variations along the DNA (single nucleotide polymorphisms, technically speaking). So, each individual DNA variation can only explain a tiny fraction of why people differ in a trait—so tiny that to call it a gene for that trait is grossly misleading.
We also know that each little DNA variation can simultaneously play a small role in many traits. For example, genes that may play tiny roles in certain personality traits can also be involved in how much we weigh or how many years we go to school, among many other things.
As a result, there is no direct link between genes and traits. Any trait level can correspond to innumerable gene combinations and the other way around: The same genetic background can lead to different levels of many traits.
Genetic Without Genetic Determinism
This is perfectly consistent with the commonsensical interpretation of why genetically similar people tend to be more similar psychologically.
Rather than being genetically wired for personality traits, people’s typical patterns of behaving, thinking, and feeling reflect the solutions they have developed for thriving with their genetically unique bodies and brains in the circumstances available to them. If circumstances were different, people could have developed other patterns; when circumstances change, people can tweak their ways. But on average, genetically similar people are always more likely to end up psychologically similar than random strangers because they have to work around similar bodies.
Because so many genes are involved in making up the different aspects of our organisms that we need to work around, they can all contribute to our psychological differences. This is what makes individual genes’ roles minuscule and not specific to any trait, exactly as studies show.
In this way, how we are psychologically partly reflects our genetic make-ups, but not because our genes determine our traits. Instead, our traits reflect how we continually try to thrive in our life circumstances, given the genetic hands our organisms have been dealt.
Facebook/LinkedIn image: Sangiao Photography/Shutterstock
