The First Rule
The first rule of behavioural genetics is that every trait is heritable. What makes us different is about 1 per cent of our entire genetic code. The other 99 per cent codes for things like brains, heads, proteins, ears, and bipedalism (ability to walk upright), the things that make us human. The other single per cent contains those DNA differences that make us who we are. This single DNA percentage has the most far reaching impact on social, economic, and psychological differences between us.
Blueprint, by American psychologist and geneticist Robert Plomin, is the product of a thrilling lifelong career in genetic research. The magisterial evidence it outlines provides a showstopping window into our very nature. From social experiments like the Colorado Adoption Studies (CAS) to biological experiments like TEDS (Twin Early Development Studies), behavioural genetics enable us to quantify the contribution of nature and nurture in terms of specific psychological traits. One way to do this is to study relatives who share the same genes (nature) but different environments (nurture). Adoption acts as a natural experiment which allows researchers to do just that. The empirical studies have consistently demonstrated that adoptive children show greater resemblance to their biological/genetic parents, rather than their adoptive/environmental parents, across almost all traits. Another way of studying heredity is by comparing the behaviour of twins, who can either be identical (sharing exactly the same genes) or fraternal (sharing 50 per cent of genes). Like adoption studies, twin studies support the first rule of behavioural genetics; that, on average, psychological traits are extremely heritable at around 50 per cent.
Three other major findings laid out in the first half of the book are the degrees of heritability, non-shared environments, and the nature of nurture. Genetics provides the majority of systematic variation between us, whilst environmental effects are random, and our chosen environments show genetic influence. Heritability is one of those tricky concepts that is easy to misunderstand. When people hear that weight is 70 per cent heritable, they often see an imaginary pie chart floating above a person’s head; 70 per cent representing genes, and the other 30 per cent representing the environment. This is a mistake. First and foremost, heritability is a property of populations not of individuals, and it explains the variance between people that deviate from the mean. If you come from a culture that arranges your marriage, your best guess of the weight or height of your potential bride would be the average height or weight of your local population. If we consider an entire population, however, all the differences from the average are what we mean by variance and identifty where heritability applies. Therefore, for weight, 70 per cent of the differences in people’s weight throughout a population is due to inherited DNA differences. Heritability describes how much of the differences between us (variation from the average) can be explained by DNA differences (the 1 per cent of our DNA that varies). It’s worth remembering that the other 99 per cent of our DNA code is what we call innate and does not vary except in rare cases. The 1 per cent of DNA that does vary is what contributes to making us who we are psychologically.
Another incredible finding is that heritability of certain traits increase overtime. The heritability of IQ and weight for instance is 40 per cent in early childhood, changes to 60% in adulthood, and rises to almost 80 per cent in later life. Life events and environments certainly leave a mark, but the influence is minimal in comparison to genetic effects. The evidence shows clear genetic trajectories for many traits. On average, 50 per cent of the differences between people are accounted for by genes and the rest by environment, but it's not the environment one usually imagines. Almost half of what we ascribe to environment is actually genetics in disguise. This is what Plomin refers to as the nature of nurture. Furthermore, parents are often responding to genetic differences in their children. The precocious child gives the book reading mother a false sense of influence. It is incredible to think that if your child was taken away at birth she'd be almost exactly the same person although raised under an entirely different roof. Incredible as it may seem, this is exactly what the evidence tells us. This led to the most infamous quote of the book, “Parents matter but they don’t make a difference”. Of course, it’s worth reiterating that we are describing the normal range of developmental upbringing and this does not apply to abusive or neglectful environments where the psychological effects would be acute and clear.
Index of Equality
Taking note of some common effect sizes is a good way to compare the influence of different factors. It is often assumed that children learn more in classrooms containing fewer children or that the quality of schools explain why children do so well. However, the correlation between the number of pupils in a class and educational achievement is only significant in so far as it is based on a large sample size, the actual effect is only 1 per cent. The GCSE is the UK’s final exam for 15-16 year old’s, and studies show that only 4 per cent of the variants in these results are explained by the quality of the school. This number drops to just 1 per cent when you correct for socio-economic status, which means that the quality of the school on outcomes is almost negligible. Schools matter but they don’t make a difference. Even though these schools have little effect on individual differences parents will still send their children and spend a small fortune, by virtue of the social networks that could be forged, and job opportunities created. Parents that cannot afford such schools can take solace in the fact that highly selective schools, unintentionally selecting for highly heritable traits, have very little impact on overall school achievement.
For a medium effect size explaining 10 per cent of the variance in educational achievement we see, unsurprisingly, parental educational attainment. If a child does well at school 10 per cent of the differences in outcome are due to parental achievement. An example of a large effect is one that explains 25 per cent of the variance, an effect you can see with your eyes closed. One example is general intelligence, and it accounts for about 25 per cent of the variance in educational achievement. There are very few large effects of this size in psychology. With the previous effects in mind and armed with the knowledge that heritability accounts for approximately 50 percent, it’s clear we are talking about an effect size that is literally off the charts. Inherited DNA differences are by far the more significant systematic force in making us who we are. Once environmental differences have been dramatically reduced, which studies already support for certain countries, the largest remaining differences are going to be genetic.
This is one of the most extraordinary implications of genetics. Instead of genetics being antithetical to equal opportunity, heritability of outcomes can be seen as an index of equality of opportunity. Equal opportunity means that environmental advantages and disadvantages such as privilege and prejudice have little effect on outcomes. Individual differences in outcomes that remain after systematic environmental biases are diminished are to a greater extent due to genetic differences. In this way, greater educational equality of opportunity results in greater heritability of school achievement. The higher the heritability of school achievement, the less the impact of environmental advantages and disadvantages. If nothing but environmental differences were important, heritability would be zero. Finding that heritability of school achievement is higher than for most traits — about 60 percent in Western countries — suggests that there is substantial equality of opportunity.
Robert Plomin | Quillette
Abnormal is Normal
Another revolutionary finding is changing the face of mental health. When it comes to psychological disorders such as reading disability, autism, depression, schizophrenia etc, it is quantity not quality that matters. For instance, there are thousands of single-gene disorders like Huntington’s or sickle cell anaemia, which are thankfully incredibly rare. These single celled disorders are necessary and sufficient. Necessary because you only get the disease if you inherit the mutation. Sufficient insofar as if you do inherit the mutation, you will succumb to it.
OGOD, as Plomin calls it, is how many people think about psychological traits- One Gene One Disorder- necessary and sufficient. However, findings from genetic studies have falsified the OGOD hypothesis and we now know that psychological disorders are the result of potentially thousands of genes each having small effects. This is known as polygenic inheritance. This finding means that we all share the genes for these disorders, but the quantity of inheritance increases or decreases the probability of suffering from any particular disorder. For instance, the average person may have 500 of the 1000 depression-causing DNA differences and will therefore have an average risk for depression. People with less of these DNA differences will have lower risk and people with more will have higher risk. Another way to express this is that the abnormal is normal. These disorders are normally distributed across a bell-shaped curve throughout the population. Does this mean we all have some degree of schizophrenia? Indeed, it does. Anyone that has meditated will have made this empirical discovery long before the genetic revolution came along.
There are huge implications here for psychiatry and clinical psychology in general. Genetic research has demonstrated that the medical model is wrong and what we call disorders are merely the extremes of the same genes that work throughout the normal distribution. This finding means that curing a disorder is absurd because there is no disorder in the first place, just dimensions along a scale. Sliding your finger along that scale and deciding on a location where a disorder begins is an arbitrary assignment. The word spectrum is already being used for conditions like schizophrenia and autism and this is a move towards a more quantitative approach. It is a case of more or less for all of us.
The Nature of Potential
Like all these propensities they are descriptions of what is, not what could be i.e potentials. If you are high on the scale for poor attention there is nothing to stop you from engaging with practices like mindfulness to make your attention deficit more manageable. Having a reading disorder does mean you are fated to a life without books. Alas, being situated low on a spectrum, like one for a sense of humour, does not mean you’ll never be funny or enjoy irony. The cosmic lottery decides who becomes a Buddha, J.K Rowling or a Rick Gervais. Nevertheless, discovering our own unique worth and dignity is far more important than becoming what parents, society, or even genetics, have in mind. Propensities significantly influence our behaviour especially when they interact with certain environments. Meanwhile, an array of potentials waits to be actualized.
Throughout our lives we are bombarded with inspirational aphorisms. The barrage also comes from pop-psychology books where the message is all you need to succeed is some panacea, such as the power of positive thinking, growth mindset, or 10,000 hours of practice. Anyone who is interested in these modern maxims should understand that, to the contrary, genetics is the main systematic force in life. That is not to say genes are destiny. It just seems more sensible, where possible to go with the genetic flow rather than swimming upstream. As W.C. Fields said, “If at first you don’t succeed try, try, try again. Then quit. No point being a damn fool about it.
Robert Plomin | Blueprint
This is exactly what we mean by actualizing our potentials. An exploration of life but at the same time an acceptance of our natural limitations. What else does it mean to mature. We vary in terms of our genes and we vary in terms of our potentials. Exploring those potentials is one of the most magnificent properties of humanity. Whilst we do vary there are at least two potentials that are universal. The first is the moral potential, the potential to feel empathy toward sentient beings. The second is the insight potential, or seeing inward, the potential to self-reflect and become aware of the subjective facts of experience- namely, those born of a false sense of self that produce needless suffering. Both these potentials interact at various times throughout our lives and are universally shared by us all. Here is a quote from Professor Plomin with an example of the moral potential for a just society as opposed to a meritocratic one.
Equality of opportunity, income inequality and social mobility are some of the most critical issues in society today. They are hugely complicated topics that heavily depend on values. My objective has been to look at these issues through the single lens of genetics, to show how DNA makes us who we are. However, no specific policies necessarily follow from genetic findings, because policies depend on values. My values, not my science, lead me away from meritocracy towards a just society.
In summary, genetics provide the majority of systematic variation between us, environmental effects are random, and our chosen environments show genetic influence. Everything is heritable - and the rest is non-shared environment or environments that are often genetic effects in disguise. Children actively select, modify, and create environments correlated with their genetic propensities. Every psychological problem is of genetic degree not of kind and we all show major polygenic influence along a normal distribution (thousands of genes having small effects). We share some propensities and potential’s, while many others are unique. A life well lived and a society well-formed is one where an understanding of propensities is known, and an exploration of potentials is possible. It is the path of the razors edge and we need not deny one at the expense of the other.
Plomin, R. (2019). Blueprint: How DNA Makes Us Who We Are (The MIT Press) (Reprint ed.). The MIT Press.
School quality ratings are weak predictors of students’ achievement and well-being
Sophie von Stumm, Emily Smith-Woolley, Rosa Cheesman, Jean-Baptiste Pingault, Kathryn Asbury, Philip S. Dale, Rebecca Allen, Yulia Kovas, Robert Plomin
Journal of Child Psychology and Psychiatry
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