In this video we take a basic look at how to understand the role of genes on personality and how evolution may shape traits and select for a range of variance in a trait rather than extremes.
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Bouchard & Loehlin, 2001 – (I should have said “paper” not “study” as it is a review summarizing many studies): https://www.researchgate.net/publicat…
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Video Transcript
Hi, I’m Michael Corayer and this is a Psych Exam Review. In the previous video I talked about the behavioral approach system and the behavioral inhibition system and we looked at the idea that people might differ in these systems and those differences might cause differences in the expression of personality. But this led us to the question of what’s causing differences in these biological systems? And a plausible answer for that might be that genes cause differences in these biological systems and that then leads to different expression of personality.
So in this video we’re going to look at the relationship between genes and personality. Now one way that we could investigate this relationship would be to do twin studies. So we could look at different types of twins who share different amounts of genes, so identical twins and fraternal twins, and then we could see how similar are they for different personality traits. And from this we can estimate the heritability of a particular personality trait. Now this is something that Bouchard and Loehlin did in a 2001 study and they looked at the relationship between genes and the Big Five personality traits. They calculated the heritability based on twins.
What they found was that for personality, Big Five personality traits, the heritability estimates range from about 0.3 to 0.6. Ok, so what are these numbers mean? Well it’s important to remember that heritability is about groups of people. It’s not about individuals. It’s not saying, you know, that your openness let’s say, let’s say it was 0.4 for openness it doesn’t mean that 40 percent of your level of openness came from your genes. What it means is that when we ask, why do people differ in openness, that the answer is about 40 percent of the explanation is that people have different genes. Alright, so that’s the first thing to keep in mind about these heritability estimates.
And the second thing to remember is that these are not set in stone; that heritability changes in different groups at different times, right? Just like we saw for IQ and so if you’re a little fuzzy on the heritability concept you might want to go back to the videos I made on intelligence and refresh sort of what heritability is. Because I went into more detail in those videos. Ok, but nevertheless, we can see this range from about 0.3 to 0.6 means when we ask the question why do people have different scores for these personality traits, about 30 to 60 percent of the answer is well, people have different genes.
But this leaves ample room for the environment, right? Certainly the rest of the reason is people have different environments and those are also shaping their personalities. Now, when we think about the role of genes in these heritability estimates for these personality traits it’s also important to remember that these don’t tell us anything about specifically how it’s happening, right? This isn’t saying oh it’s levels of neurotransmitters or maybe it’s receptors or transporters or maybe it’s hormones. We don’t know what the genes are actually affecting to cause these differences we just know that genes are partly responsible for the difference in personality between people.
Ok, now another way we can see differences in personality that seem to be due to genes is looking at temperament. So temperament refers to the personality of very young infants, who really haven’t had much environmental experience yet. So we see differences in infants in their levels of activity, their levels of sociability, their levels of emotionality. And these differences are apparent from a very young age, right? When they haven’t had much environmental difference yet. They haven’t had much environment to be influencing them. We also see these differences between children raised by the same parents, you know, so we can assume those environments are fairly similar. And yet, you know, one child is, you know, very emotional and prone to tantrums and screaming and crying and the other is a very calm child. And so that would suggest that it’s not the the parental environment that’s causing those differences between the children. It’s more likely to be something that’s caused by genes.
Now if we start thinking about genes and biological systems as controlling how we express our personality then that leads us to wonder about animals. Do animals have personalities? Certainly they have differing behaviors and dog owners might say “yes, my dog has a unique personality, totally different from all other dogs” but other people might not be so sure. We might wonder well, if dogs express this then do cats have different personalities? Maybe cat owners would say yes, well what about, you know, chickens? And a farmer might say, you know, this chicken is more socially dominant here, this chicken wanders off to explore more readily than others. And we can even find differences in Big Five personality traits for something like an octopus. So what we can do is measure something like openness to experience and we can measure that by putting an octopus in a new environment and seeing how much they explore. Do they stick to the one area that they sort of know or do they explore the entire tank? And maybe that tells us something about personality for an octopus.
And if we start thinking about the role of biology and genes in personality then pretty soon we’ll find ourselves asking about evolution. What’s responsible for the variance in these traits and how has it been selected for over time? So are there evolutionary advantages to certain traits? We might think of something like agreeableness and say, you know, people vary on agreeableness and we can maybe come up with some different ways that agreeable this might be advantageous to survival in certain situations. So we might think okay, you know, if there’s a famine and people are willing to cooperate and share food and share resources that group of people is going to be more likely to survive than the group that’s sort of every man for himself, you know? And as a result everybody dies.
So we could come up with some explanations for that. Now that’s not saying that agreeableness is always a good trait. We can certainly come up with other situations where we can see that disagreeableness would be advantageous and this brings up the idea that variance is important when we talk about traits and evolution. We’re generally not going to find that there’s a superior trait. It’s only superior in terms of the environment that it’s in. So sometimes high agreeableness would be a very good thing, sometimes low agreeableness would be a good thing, right? And in this way we can see that evolution can provide sort of a stabilizing force on certain personality traits where they don’t get into this sort of positive feedback loop and become extreme because the extremes are less likely to be advantageous.
So we think of something like sociability, neither extreme is a particularly good thing. Because let’s say that you’re extremely sociable and you just constantly need to be around other people. Well there’s going to be times when you have to be alone and you’re not gonna be able to deal with that very well if you’re extremely high in sociability. At the same time, of course, if you’re extremely low in sociability and you can’t seem to talk to anyone, right? That’s obviously not going to be advantageous either because there are times where you have to interact with other people. And so what happens is we get this sort of stabilizing where we’re pushed away from the extremes to a balance where, you know, we have something in the middle for these different traits. And we could make this same argument for any number of other traits as well, right? And so we can then think about how the variants and traits that we see is the result of these evolutionary forces.
Ok, so that’s all the detail we’ll go into for genes and personality. We’re not going to get into specific genes and things like that but we’re going to move on in the next video and start thinking about other ways of looking at personality. And we’ll start by looking at a socio-cognitive approach to personality. So I hope you found this helpful, if so, please like the video and subscribe to the channel for more. Thanks for watching!
