What is the optimal amount of time and effort you would put into your dream before giving up? How many poor LSAT scores will it take for you to realize that you might not be cut out for law school and should pursue another career instead? Are some people just naturally better suited to a career than others? If you’re having a tough time on these questions, don’t beat yourself up – even those who consider themselves experts in relevant fields cannot come to an agreement. I’ll try shine some light on it but in short – life is tilted and the angle of the tilt may be the answer. More on that later in part 4, first we need some background. Here’s a trajectory for our exploration:
- Part 1: The DNA revolution
- Part 2: DNA makes us who we are
- Part 3: DNA is not destiny
- Part 4: It’s the tilt in the web that matters
Part 1: The DNA Revolution
Over the last two decades, our understanding of genetics and who we are has seen an exponential curve. We went from sequencing the first human genome in 2003 for several billion dollars, to being able to get it done by companies such as 23andme for a few hundred dollars today. It is a very dynamic industry with huge potential in the coming years. For those interested, a deeper dive on the future of the genetic revolution is available here.
Today, we will ignore the future potential but instead focus on arguably the cornerstone issue of genetics – to what extent does our DNA shape who we are? Regardless of the progress we have seen in this space, the jury is still out.
Part 2: DNA makes us who we are
In 2018, Robert Plomin, arguably the world’s leading behavioral geneticist, published Blueprint: How DNA makes us who we are, the culmination of several decades of his and other research into behavioral genetics. To many, especially those who only skimmed the cover, this book yelled genetic determinism. However, not so fast, it’s more nuanced than that.
In a nutshell, regardless of how provocative Plomin tries to be with his title – he does not make an argument for genetic determinism. He does not say that DNA is destiny. Instead, he argues that genetic factors are the largest factor that explains the world that is. For different psychologic traits, genetic differences account for between 40% to 70% of difference between individuals. Plomin does not make these arguments about a world that could be, but only the world that is. And that is a key distinguishing factor ensuring that his argument is not plain vanilla genetic determinism.
It is the strength of these probabilistic propensities versus other factors in how they contribute to who we are that makes Plomin’s argument unique. He argues that these genetic nudges are in fact so strong, that once we are aware of them, it would be silly to fight them.
But if only 40% to 70% of variation between individuals is due to their genetic differences, then environment must surely play a huge role. Plomin agrees, but its not the environment you’re thinking about. Plomin argues that “environmental effects are important too, but they are unsystematic and unstable, so there is not much we can do about them.” Our parents? Our schools? Unstable and unsystematic?
No, our parents and schooling are systematic, they just don’t make a difference in shaping who we are – according to the research that is. Plomin’s dense research shows that systematic environmental factors such as being raised in shared environments do not make a difference in who we are – referring to psychological outcomes. The environmental factors that influence who we are, happen to be idiosyncratic and random, not the controlled ones as is often believed.
The conclusion comes from adoptive sibling studies (where one sibling is biologically related to the parent and the other is adopted). The findings show almost no correlation in psychological trait measures between the siblings. Further, “the correlations between the adopted children and their adoptive parents, who share nurture but not nature, hovered near zero.” Had environmental factors within the household shaped who we are, these siblings would likely exhibit much stronger correlations in psychological measures with each other and with their adoptive parents. To compound the shock, the adopted sibling and their biological parents, share as high a correlation as parents and normally raised children do – supporting the idea for strong genetic influence.
Part 2 TLDR: Ultimately, Plomin argues that the largest factor that shapes who we are is our DNA. He makes it clear that you can change yourself, but why would you fight against the grain? Why would you beat your head against the wall for something you may just not naturally be suited for? Find your strengths instead. I’ll end this part with what must surely be Plomin’s favorite quote:
“If at first you don’t succeed, try try again. Then quit. There’s no use being a damn fool about it.“W.C. Fields
Part 3: DNA is not destiny
Steven J Heine, a professor of social and cultural psychology at the University of British Columbia, is convinced that our DNA does not dictate our destiny, and instead that society completely misunderstands the relationship we have with our genes.
In his book, DNA is not Destiny, Heine argues epigenetics and environment play a far larger role than Plomin gives them credit for. It’s the typical nature versus nature argument but we are not going to dig into that here because then we have to start thinking about the ‘nature of nurture’, and start talking about statistical biases. That is not what we are here for.
Instead, let’s dig into Heine’s idea of web-based thinking. The idea that our phenotypes (gene expression), are a product of a complex web of our genetics, epigenetics and our environments – each of the many different influences on the web pulls us in a particular direction. This is vital, far too many people believe that there are intelligence genes, or height genes. This is what Heine calls switch-based thinking, the belief that single genes determine complex outcomes. To provide perspective, even a phenotype as ‘simple’ as height has 294,831 SNPs (Single Nucleotide Polymorphisms, pronounced ‘snips’), or individual DNA differences, associated with it. Although sometimes it may be a single gene, most of the time it’s pretty complicated.
Heine asserts that phenotypes are not predetermined, it is possible to change your position on the web. The web “might be tilted so that it’s easier to move in one direction than the others, but ultimately there is no single force that is determining your position.” The web certainly provides resistance, or an uphill battle, but still allows for freedom.
Heine eloquently points to some limitations of Plomin’s work by highlighting ways in which heritability estimates may be upwardly biased. He makes strong cultural arguments suggesting that the outcomes of adoptive and twin studies may be limited to the societies in which they were developed. However, Heine himself admits that there are “strong genetic contributions to traits such as intelligence, personality, self-esteem and the likelihood of developing schizophrenia.” It’s all about the first law of behavioral genetics – “all human behavioral traits are heritable.”
An argument that Heine flirted with, but certainly didn’t drive home, is that even if DNA does have a strong role in shaping who we are, other environmental, cultural, social and economic factors may play a larger role in where we end up. That is even if expensive schools don’t make students better, as Plomin would argue, they certainly provide extensive opportunities and open doors to elite universities, which in turn set the platform for almost any student to relatively easily kickstart their career.
Although not directly related here, Heine deserves credit for calling out genetic testing companies for overselling their products and their potential to tell us about ourselves. Companies such as 23andMe often use unreplicated and conflicting scientific studies to make substantial claims. For some traits the evidence is strong, but they are communicated in a sensationalist, and misleading way.
An increase in risk from 4% to 7% for a given disease is communicated as ‘you have a 75% higher chance of developing X than the average individual’, rather than communicating it as a 3 percentage point change or that ‘93% of people with similar DNA to yours will not develop the disease later in life’. But that’s the beauty of statistics, the numbers can tell whatever story you want them to. So the lesson from this sidetrack is – if you are going to partake in these commercial genetic tests, take the results with a grain of salt, and do your own research too.
Part 3 TLDR: Ultimately, Heine does not argue that DNA does not play a role in shaping us. He instead argues that genetic influence is overestimated and that cultural, environmental and epigenetic factors should not be overlooked. “You have freedom” he would argue, “fight against your genetic predisposition.” (to be clear – he didn’t actually say this, but I bet he would)
Part 4: It’s the tilt in the web that matters
So these two very distinguished scholars agree on almost everything. There is one major point that they disagree on, and that is the angle of the tilt in life’s web (this is a different concept from Heine’s web-based thinking, so try put that idea away for a while). The tilt in this web is all about the strength of genetic probabilistic propensities, or the firmness of the genetic nudges. Heine will argue the nudges are subtle, Plomin instead convinced that they’re so firm you could be a damn fool for fighting against them. Allow me to (try) illustrate:
Imagine yourself, situated at the center of the web, everything you have ever dreamed of sits at the edges (here labelled A through J due to lack of creativity). In a perfectly idealistic world, the web would be flat and everyone’s chances of succeeding at the same task would be a function of time, effort and education. In reality, that’s not the case, the web is tilted.
The web is tilted so that ‘A’ may be easier to achieve than ‘F’. This is the case before you enter the world – and unfortunately there is not much you can do about this. ‘A’ may come naturally whereas ‘F’ would require more effort, a subtle genetic resistance holding you back, but certainly not something you cannot overcome. This is the world that Steven Heine lives in, a world of weak genetic propensities.
But now imagine a world where this web is radically tilted to an almost 90 degree angle. To get to ‘A’, you merely slide down a purple slide on your web, because your genetic predisposition for ‘A’, whatever that may be, is so strong that it just comes naturally to you. However, ‘G’ or ‘F’ are not as easily reachable. Due to the extreme tilt, you stare almost directly upward at it. It’s like looking up at the top of a rock climbing wall, maybe with some snakes on it to make it even tougher, you feel there is no way you could get there. This is more than a mere genetic resistance. This is an almost insurmountable uphill battle. It may require you to put in years and years of blood sweat and tears, and in the end you may still fall short. This is the world that Plomin lives in, a world where genetic propensities is the most important thing in shaping outcomes.
So that’s it ladies and gentleman, the biggest disagreement in a field as complex as behavioral genetics is about the slope of that web’s tilt. And that tilt, however large it may be, could be useful in deciding when to give up. You must be thinking: “Okay – so I came here to find out when to give up, but I still have no idea.” Thats fine, because it’s really not so clear. The answer, as we know, lies in the slope and direction of our web’s tilt, but can we ever know it?
According to Plomin the answer is yes, and it comes in the form of what is called a Polygenic score. In our web analogy, your polygenic score would hold information on the slope and direction of your web’s tilt – in other words, that ‘A’ is easier to achieve than ‘F’, or that ‘C’ would be much much easier than ‘H’. Today, it is still a rough measure, but with the genetic revolution taking hold, and data processing powers increasing, polygenic scores are expected to within the decade predict academic success, athletic ability and susceptibility to diseases and mental disorders. Stop and think about that for a second – some saliva from your newborn child will be able to capture her full genetic potential for educational attainment—along with her genetically predicted height, and risk for various diseases.
So if by 2030 the predictive power of the polygenic scores turn out to be as strong as their proponents claim, we would know that life’s web is steep. However, if over the next decade or so our accuracy of predicted traits from genome sequences do not rapidly increase, it means that other factors – epigenetics, environment and culture instead are the greatest determining factors in who we are, in other words rock climbing walls with snakes are not real.
But think about it for a moment – if the predictive power of polygenic scores were to increase, would you want to know your polygenic score? Would you want to know the direction and steepness of the tilt in your web? If the direction of your tilt went away from what your dreams desire, would you quit or would you be a damn fool about it?