Monday, December 10, 2012

Tabula Rasa: Do genes influence personality?

wikipedia.org
If I were to ask you the simple question, "Do you think that genes influence your personality?" The first thing you might think, is that I'm asking you a stupid question. After all, nearly all our lay beliefs about the world include beliefs that some of our genetic material influences who we become as people. And though we do believe, to varying degrees, that our experiences shape who are, I'm sure we can't think of all that many people who believe, like Aristotle, that we are a tabula rasa (blank slate). As well, if you believe in evolution then you must have an implicit belief that genes influence who we are. If evolution has taught us anything, it is that survival means passing on the fittest of our genes to the next generation.

So, you come to PYM today with the implicit belief that your personality is most certainly influenced by your genes. What if I told that this is not what the most recent research in behavioral genetics would suggest?

Genes and Personality: The Early Years
In the early years examining the links between genes and personality, it was typical for a study to examine self-reports of personality and compare the self-reports between fraternal twins--who share roughly 50% of their genes--to those of identical twins--who share 100% of their genes. In these early twin studies, very consistent effects emerged that suggested one thing: when it comes to personality, genes matter.

Nurture is really whooping Nature today on PYM
In that work, researchers calculated heritability estimates--in lay terms, the amount of variation in personality that is explained by genes--by examining personality similarity between twin pairs. For identical twins, heritability estimates hovered around 46%, and 23% for fraternal twins (a heritability of 1.00 means that all variance is genetic; Jang et al., 1996). Together, this early work was very clear in its suggestion that there are some genetic influences on personality. The next question, was of course, which genes would be the biggest players in the gene-to-personality pathways?

Candidate Genes
The early work in twins is suggestive of the possibility that eventually, with enough knowledge about human DNA, scientists will be able to discover a specific gene for, well, for anything related to personality, preferences, intelligence, or physical characteristics. That's a potentially exciting domain of future research, and one that researchers have examined very vigorously in the last 15 years or so. In this work, affectionately referred to as "gene for.." studies by one of my colleagues, researchers looked for specific small repeating sections of genes (single nucleotide polymorphisms or SNPs) that identified a version of a specific gene. The SNPs usually were related to the specific production or reception of neuropeptides implicated in any number of social behaviors in non-humans. One really famous SNP is the APOE4 genetic polymorphism, which has been linked to increased risk for Alzheimer's Disease in humans. Another one is the GG variant of the oxytocin receptor gene rs53576, which is associated with increased oxytocin receptors in the brain.

The critical point in these "gene for.." studies is that, if we know what parts of personality that a specific neuropeptide influences, then its genetic variants should predict behavior in a similar fashion. More specifically, knowing how oxytocin influences personality (although oxytocin's influence on behavior is still in question) would suggest that knowing variations in specific SNPs on the oxytocin receptor gene should help us predict personality.

In the subsequent "gene for.." research, many researchers were left disapointed. Specifically, for every breakthrough finding linking a specific SNP to a personality characteristic, there was a null replication. Several of the most promising candidate genes, such as the MAOA gene which has been linked to antisocial behavior in past research (Caspi et al., 2002), have failed to replicate in subsequent work, according to several meta-analyses (De Moor et al., 2010).

So, then genes don't influence personality?
This will pay for a few gene studies!
The current prevailing genetic evidence seems to suggest that we actually don't have genes for personality. And this conclusion doesn't come from a lack of trying: The US government has spent billions on genetic research. Billions. BILLIONS!!! When I think about all the $$ that went into this "gene for.." research, I want to throw myself out the second floor window of the psychology building. The fall wouldn't kill me, but I imagine it would hurt just as bad as it does to realize that much of our research funding was flushed down the "gene for.." toilet.

Of course, the conclusion that genes don't influence personality is most certainly wrong, after all, we have decades of twin research showing similarity in personality between identical twins. At least some of that similarity has to be genetic. Are we missing something that might help uncover the great mystery linking genes and personality?

Take a longer look at the genes.
One potentially promising approach involves examining many candidate genes that relate to a specific biological system associated with personality. In one such approach, Jamie Derringer led a consortium of researchers in an examination of a collection of SNPs associated with Dopamine in prior research, and then examined associations between this collection of SNPs and sensation seeking behavior. Sensation seeking is a personality trait that is linked to a number of behavioral disorders relating to substance use and addiction--and much of the human and non-human research indicates that dopamine plays a role in this behavior.

This work differs from the "gene for.." research of the past because it doesn't rely on the association of a single SNP related to dopamine influencing sensation seeking. Rather, the study looks at a number of SNPs related to dopamine in prior research, to determine if these SNPs work in concert to influence dopamine levels, and sensation seeking more broadly. This approach is appealing because it involves conceiving of genes and personality not as simple one-to-one relationships, but instead, as complex systems of genes that work in concert to express a personality trait.

The findings of this research were promising: Taking into account all the SNPs associated with sensation-seeking behaviors as an aggregate, dopamine genes worked in concert to explain around 6.6% of variation in sensation-seeking behavior (Derringer et al., 2010).

We're still not there yet.
Remember that twin studies suggested that 40% of identical twin personality was genetic? Well 6.6% in the dopamine genes study is a far-cry from 40% in this twin research. Where does the rest of the heritability go?

One possible answer arises from understanding what happens to DNA before it is expressed as a personality characteristic. As your high school biology instructor will tell you, DNA is a code for building proteins, hormones, and neuropeptides that serve specific cellular functions within the body. One thing that early gene-personality work overlooked is that a lot has to happen to allow DNA to code for specific hormones/neuropeptides, that then have to act at the cellular level to subsequently influence personality. In short, genes need to be expressed at a cellular level in order to influence personality, and so one place where a genetic researcher might want to look to examine gene influences on personality is at this expression--that is, what genes are being unzipped by RNA, so that specific hormones/proteins are produced?

Research in honey bees is suggestive of the potential of examining RNA to predict behavior. In this work, messenger RNA abundance was a significant predictor of behavioral transitions of honey bees from hive workers to foragers (Whitfield et al., 2003). Human work in this domain is an exciting area of future research.

If you've made it this far, you can appreciate (like I do), that the question: "Do genes influence personality?" cannot receive a simple answer. On the one hand, genes clearly seem to contribute to personality, but on the other, much of the genetic evidence has not supported this view. I'm cautiously optimistic about the future of gene work. Are you?


Whitfield, C. (2003). Gene Expression Profiles in the Brain Predict Behavior in Individual Honey Bees Science, 302 (5643), 296-299 DOI: 10.1126/science.1086807

Derringer, J., Krueger, R., Dick, D., Saccone, S., Grucza, R., Agrawal, A., Lin, P., Almasy, L., Edenberg, H., Foroud, T., Nurnberger, J., Hesselbrock, V., Kramer, J., Kuperman, S., Porjesz, B., Schuckit, M., Bierut, L., & , . (2010). Predicting Sensation Seeking From Dopamine Genes: A Candidate-System Approach Psychological Science, 21 (9), 1282-1290 DOI: 10.1177/0956797610380699

de Moor, M., Costa, P., Terracciano, A., Krueger, R., de Geus, E., Toshiko, T., Penninx, B., Esko, T., Madden, P., Derringer, J., Amin, N., Willemsen, G., Hottenga, J., Distel, M., Uda, M., Sanna, S., Spinhoven, P., Hartman, C., Sullivan, P., Realo, A., Allik, J., Heath, A., Pergadia, M., Agrawal, A., Lin, P., Grucza, R., Nutile, T., Ciullo, M., Rujescu, D., Giegling, I., Konte, B., Widen, E., Cousminer, D., Eriksson, J., Palotie, A., Peltonen, L., Luciano, M., Tenesa, A., Davies, G., Lopez, L., Hansell, N., Medland, S., Ferrucci, L., Schlessinger, D., Montgomery, G., Wright, M., Aulchenko, Y., Janssens, A., Oostra, B., Metspalu, A., Abecasis, G., Deary, I., Räikkönen, K., Bierut, L., Martin, N., van Duijn, C., & Boomsma, D. (2010). Meta-analysis of genome-wide association studies for personality Molecular Psychiatry, 17 (3), 337-349 DOI: 10.1038/mp.2010.128

14 comments:

  1. My Dad was funny and tall.
    My Mom is not funny or tall.
    I'm funny and tall.
    I'm even told by those who know that I'm funny like my dad (and 3 inches taller).
    My parents divorced when I was 2, and my Dad lived so far away that I really only saw him once a year.
    No one has any problem acknowledging the heritability of height.
    Many people balk at the heritability of humor.
    But it must be the genes since environmentally my Mom had way more influence on my development.
    Right?

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    1. That's a nice anecdote Mitch, and I think that most people have some experience like that with their parents (divorced or otherwise).

      That's what is so interesting about how recent genetic work doesn't find "gene for.." associations. The smart money is with you Mitch, in that gene researchers don't yet, but will soon, have the tools and insights that can capture the genetic influences on personality. The future will be exciting.

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  2. I suggest reading the following to see why no such genes have yet been discovered, nor will not be:
    Wahlsten, D. (2012).The hunt for gene effects pertinent to behavioral traits and psychiatric disorders: From mouse to human. Developmental Psychobiology, 54, 475-492

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    1. Thanks for the paper recommendation, Gary. I think it's cynical to believe that genes don't influence personality--more likely, they do, we just don't know how to measure the genetic influences all that well right now.

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    ReplyDelete
  4. Michael, I don't really like this blog post.
    You completely fail to mention that this pattern of results is the same for any complex trait under study.
    It's also misleading to simply state the amount of money that went into "Gene for…" studies. Only a fraction of these relate to psychology, even fewer to personality. And for Mendelian inheritance patterns, which we find for many debilitating diseases, "Gene for…" studies were very successful.

    There are interesting differences in the pattern of results when it comes to genome-wide complex trait analyses (for example for height, intelligence: a lot of additive variance vs. personality, not much additive variance), but these aren't mentioned.

    Mitch, it's not "either… or" for complex traits. The correlations between parents' and children's personalities aren't very high, it might surprise you to know. So maybe you being funny is something environmental, unrelated to your mom. You did get out sometimes, didn't you?

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    1. Thanks for the comment. Sorry you didn't like the post, but I didn't promise, nor deliver, a completely comprehensive account of genes. The spirit of the post was to point out how much work there is left to do regarding genes, including with respect to examinations of epigenetics, and additive gene effects. This is of course, not an exhaustive list, and you point out some very interesting other avenues of future research. Thanks for that, and for reading!

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  5. I think this is the most insightful blog post I've seen in ages.

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    1. That's nice of you to say! Did your genes influence this comment? ;)

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  6. I think it might be wise to consult a basic behavioral genetics text before writing extensively about it. For example, the comment that heritability is different for monozygotic and dizygotic twins is nonsensical. Heritability is a population-level estimate that can be derived by comparing twins (or a variety of other techniques such as GCTA which compares unrelated individuals based on measured genetic similarity). You might also want to consult work on gene-environment interaction or correlation as it provides more intuitive reasons why GWAS has failed...or anything Turkheimer has written really.

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    1. Thanks so much for reading! From what I understand about your comment, you're suggesting that the wording of the portion on heritability is off--b/c researchers use MZ and DZ twins to derive heritability estimates? It sounds like you're right, that could have been worded better.

      Other than that though, I'm not really sure how this comment adds to the discussion. If you want a discussion of gene-environment interactions, we've discussed Turkheimer's work on this blog already (http://psych-your-mind.blogspot.com/2012/04/genes-and-power-of-situation.html). If you'd like other explanations for why genome wide association studies have failed, you could, I don't know, maybe write your own blog about it... This isn't a peer-reviewed journal article.

      Thanks again for reading!

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  7. Michael, Great Post!

    Way back in 1986, John Bowlby suggested: Personality structure is the level of vulnerability to adverse life events and situations.

    However, it’s more nuanced than that. He asked:

    Does an individual view life as enjoyable, to be lived to the full, and emotionally rich and varied?

    or...

    Does an individual view life as a burden to be endured and an emotional desert?

    (The difference between the two is one's level of resiliency)

    He also suggested that:

    Transactions are constantly occurring between a developing personality and the environment. A personality moves through life, with the particular pathway followed being determined by the interaction of the personality as it has so far devleoped and the environment in which it is then finding itself.

    As Attachment applies:

    If family conditions are favorable the pathway will start and continue within the bounds of healthy and resilient development. If unfavorable conditions develop, the pathway may become deviant.

    *So to answer you question from the point of view of a counseling psychology grad student specializing in attachment theory, I believe that personality is a product of genetic influence, but greatly influenced by our earliest relationships as far as how we learn to use others feedback to regulate and understand our own emotions. It is through human contact that we develop our internal working models of the world which we (by age 5 or so) use almost completely unconsciously to predict and negotiate the constantly changing world we move through.

    Bowlby, J. (1988). A secure base, parent-child attachment and healthy human development. Basic Books (AZ).

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    1. Gosh I love Bowlby! It's been almost 10 years since I read some of his works--really inciteful! I like the idea of gene-early environment interactions that influence personality. I think that you're right Daniel, the early attachment relationships, where we spend the majority of our early lives and develop working models of the self, are likely to be one of the most powerful environments that determine the expression of our genes.

      Very exciting discoveries just waiting to be made in this realm! Thanks for the comment!

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  8. This information has been very useful since starting my research into personality psychology. I will return over and over for more inspiration.

    ReplyDelete