Robert Plomin - GCSE genes
Kat - We often talk about things being "in the genes", from traits such as eye or hair colour to our risk of diseases. One of the main ways that scientists figure out how much a particular characteristic is down to genetics - known as its heritability - is by comparing identical twins, who share 100 per cent of their genes, with non-identical or fraternal twins, who only have 50 per cent of their DNA in common. Thanks to a unique study tracking thousands of pairs of twins as they grow up, Professor Robert Plomin and his team at King's College London have now discovered that genetics makes an unexpectedly large contribution to children's GCSE grades across a wide range of subjects.
Robert - In this twin study which we call the Twin's Early Development Study which is a study of about 7,000 pairs of twins in the UK, I was interested in focusing on an area that hasn't been studied much and that's school achievement. So on the one hand, we know that cognitive ability like intelligence shows substantial genetic influence. But people hadn't really studied the business end of it in terms of school achievement. And so, we were surprised to find from the very first years of school that school achievement as measured by the national curriculum scores. It's very highly heritable, like 60 per cent heritable. That means, of the differences in children's performance in the national curriculum test, over half of those differences between children are due to DNA, genetic differences, between them. So, we're not identifying the DNA, but we're using the twin method to estimate, not only the significance, but the effect size of genetic influence on school children. It's very high.
So, we've been following them all along and now that they hit 16, we wanted to use the GCSE scores - there aren't many countries where the same national tests are administered to everybody. And so, what we've found is the same sort of thing that GCSE scores are highly heritable. But what's new is that all the tests - there's over 80 subjects that people can take for GCSEs - and all of them are highly heritable. That surprised me because I would've thought the STEM subjects - science, technology, engineering, math - would be more heritable for some reason maybe because it involves intelligence to a greater extent than drama and art. This is just totally exposing my biases of course as a scientist, but it wasn't true. They are all equally heritable. It's interesting that scores are as equally heritable despite the fact that some children are getting tutors and going to schools that have prepped them for GCSEs. Schools - we make a big deal about schools - you just say what school our kids in explain far less than 20 per cent of the variance. Explaining 50 per cent of the variance with genetic differences is extraordinary when education totally ignores genetics. In teacher training or whatever, not a word is said about genetics. And so, I'm just saying genetics is very important.
But what's really novel about this study is a little bit harder to understand and that is to say, "Okay, genetics affects all of these GCSE subjects" but is it different genes for every one? Are there genes for drama, genes for music, and genes for math? And the answer is definitely not. The same genes are affecting performance on all of these GCSE scores. The differences are probably more environmental. If you're good at drama and not good at math, that's probably more of an environmental thing. But the genetic action has to do with what's in common in performance across all of these things.
Kat - Is it not just that they're just generally smart? They've got good intelligence genes?
Robert - That's what most people would say and so, what we did is we took out intelligence. We corrected for intelligence. You can correct scores for age and sex, and you can correct scores for intelligence. So, you can take these GCSE scores and make them independent of intelligence, statistically. And then the interesting thing was that we got the same results. So, everything is equally heritable, independent of intelligence, and what's even more surprising, again, it's the same genes that affect all of those intelligence corrected GCSE scores. So what that means is that, your hypothesis is a good one that a lot of what the genetic correlation among all these GCSE scores is about intelligence. But what's amazing is you take out intelligence and you find, yes, there's still genetic influence, but it also works in a very general way and that's suggests it's like an academic ability, genetically driven academic ability.
Kat - When you say that this ability, this academic ability is heritable, does this mean that we can pin it down and say, "It's this gene. It's that gene. It's this gene"? Can we find these genes?
Robert - Well, a first step in trying to find genes is to find something that's heritable. The research over the last few years is saying that cognitive abilities and now school achievement is highly heritable, motivates people to try and find genes. But what we know so far from all of the life sciences is that for complex traits - that it's not for the thousands of single-gene disorders that are very rare, but for the common disorders in medicine like cardiovascular disease or obesity, or psychiatric things like alcoholism and depression - they're heritable but they're not due to one gene by any means. We're thinking now there's thousands of genes of very small effect which means it's going to be extremely difficult to identify the specific differences responsible for the heritability. But it's all part of a package. It would be nice if we're just talking about a handful of genes - the genes for math or something like that. But if this is what we're finding, then we're just going to have to roll up our sleeves, get the strategies that will allow us to identify, not the gene or the few genes, but thousands of genes that are responsible for the heritability of these complex traits.
Kat - King's College London's Robert Plomin, whose study came out in the journal Nature Scientific Reports. We'll be looking in more depth at his twin study - as well as other large-scale genetic studies - in next month's podcast.