There are a lot of things we get out of our genetic code. Eye color? Check. Hair shape? Check. Risk of hypertension, cancer, and other Bad Things? Check, check and check (dang it). But now, some research suggests that you can even put intelligence on that list. This is going to be quite the doozy, since this is one of things that is often argued about in the ‘nature vs. nurture’ debate.
If you’re not familiar with it, click the previous link, but the even shorter version of it, at least from a cognitive scientist and all-around smart-aleck, is what contributes more to who we are: biological factors (particularly our genetics), or our environment (including, but especially, our upbringing)? See, there’s a case for one more than the other, and it might even depend on what trait you’re talking about. Let’s throw an example out there – aggression.
What would make someone aggressive? If you were to think in only ‘nature’ terms, you could argue that a genetic predisposition to production of testosterone could contribute. In other words, what could make someone aggressive is pretty much being a guy. No wonder June Stephenson proposed a tax on men. Although if that were true, that means that only men can be aggressive, and women can’t. If you responded to that sentence with a cocked eyebrow, that is the correct response. My sister point-blanked me in the head with a Nintendo 64 controller once upon a time. From the other camp, if you were to think in only ‘nurture’ terms, you may mention their environment, such as living in a highly unstable region of the world. Makes sense, since people (especially kids) who grow up or have an extended stay in that kind of environment may take an aggressive stance in life in order to survive. If it is absolutely true, explain Malala Yousafzai or Viktor Frankl. See how difficult it really is? It’s hard to pinpoint that ONE THING that makes A lead to B, and it rarely is ever THAT ONE THING, whatever it is. Human psychology is tough.
Genetics is no different, either. According to the paper (finally we get back to the paper, geez), “single-nucleotide polymorphisms” have only a small effect on human behavior.
OK, rushed into the vocabulary there, sorry. We all know what DNA is, so I can skip that. See, DNA is made up of genes, and each gene is made up of a sequence of nucleotides, which are sequences of four chemicals that I’ve explained here. A single strand of DNA could contain several genes at once, which means that that particular DNA strand can be expressed by the body in all sorts of ways, including (but not limited to) eye color, hair color, height, and so on. With the right nucleotide sequence, you get some gene that does some thing. So, if JUST ONE nucleotide just happens to change (point mutation), weird things can happen, some of them not good. Or, it may not really affect anything at all because that nucleotide change was redundant. However, behavior (including intelligence) is much more complicated than when your eyes go from one color to another over the course of your life (which can happen, and it doesn’t affect your vision).
Back to the paper – the authors assert that a single nucleotide (which could point-mutate for any reason, but may not do anything anyway) can’t determine very well whether a child will be smart or not. At the genetic level, maybe. DNA from a large number of individuals (N = about 7000 school-aged kids in the UK) were collected to figure out what their genes were, then paired their scores with knowledge exams that they’ve taken. If you’re British (a lot of Britons seem to tune into sci.casual and that’s great), the following may be relevant and/or cringe-inducing – the exams they used were for the National Curriculum (maths and English) for 7- and 12-year olds and the General Certificate of Secondary Education (GCSE) for 16-year olds. They also measure g, or general cognitive ability, against what genes they carry. Just to cover their bases, they also looked up other factors such as socioeconomic status (SES). They also limited this to youngsters with only (maybe predominantly?) European ancestry so that it doesn’t show up as a variable. It’s not necessarily racist, you just really want to limit the things that could explain the results of your model. For example, if you’re doing a study on the predation patterns of female cheetahs, would you throw in male emperor penguins? Extreme example, but you see what I mean.
Back to the burning question: do genetics play a factor in a child’s intelligence? Using what they call a genome-wide polygenic score-
Sorry, by looking at how often certain genes show up against exam scores, the authors were able to conclude that genes do explain the trends in scores significantly – the higher your genetic ‘score’ (which means you’ve got the right genetics), you do better on those tests. The kids’ genetic scores are also related to their general cognitive ability.
(I can feel some of you getting nervous as you read this, but wait, there’s more!)
When considering SES, kids from families with low SES will have lower exam scores than kids from families with high SES regardless of ‘genetic score’. There’s more social commentary involved in this result than I’m comfortable with, so I’ll leave that for another discussion (I’ve got my own opinions as a former high school teacher). While kids from low-SES have lower general cognitive ability than kids from high-SES, it turns out that genetics is not that big of a factor with regards to general cognitive ability.
What’s the takeaway from this? One way to take is that kids’ station in life (their nurture, if you will) plays a larger part in their intelligence than their genetics (their nature). That, and perhaps being in a higher SES means that they’ll do better in exams, but that says more about society than what these kids are packing in their DNA. Is it hopeless? Here’s the thing: genetics doesn’t explain half the story (stats nerds out there: it doesn’t account for a lot of the variance in the correlation). Even the authors assert that “individual differences in educational achievement are partly due to DNA differences…and are not solely created by environmental forces.” I’ve also written a snarky post about putting so much face value on statistics-heavy studies and misinterpreting them, so let’s get a few things down:
- This was specifically done in the UK.
- This was only done with kids who previously participated in studies where their DNA was taken (even though it’s probably randomized).
- Only kids with European ancestry were considered, but it’s not clear where in Europe they were from, and how far back the ancestry search was.
There’s still some stuff to consider, a lot of which seem to be nurture-related, before we can effectively conclude that your genes determine how smart you can possibly be. Let’s not forget two things before I can finally end this post:
- “Be pitiful, for every man is fighting a hard battle.” (Ian McLaren, The British Weekly, Christmas edition, 1987)
- ‘Moneyed’ doesn’t automatically mean ‘smart’. Consult any celebrity tabloid and Twitter account for examples.
Featured article: Selzam S, Krapohl E, von Stumm S, O’Reilly PF, Rimfeld K, Kovas Y, Dale PS, Lee JJ, Plomin R. (2016) Predicting educational achievement from DNA. Mol. Psychiatry. 10.1038/mp.2016.107
Featured image: Wikimedia Commons (CC-BY-SA-20, Author: Lourdes S., 2007)