Robert Plomin – Blueprint (the Nature Of Nurture)
Robert Plomin is a psychologist and behavioral geneticist at King’s College London and the president of the international Behavioural Genetics Association. He is one of the world’s leading experts in how genes affect human personalities.
Plomin’s new book ‘Blueprint’ explains in fine (but admirably clear and digestible) detail the most up to date research findings in the field of behavioral genetics. Among the many fascinating concepts discussed in the book is the Nature of Nurture finding.
Genetic Differnces Cause Differences in Personality Traits
‘Blueprint’ deals with personality and explores the extent to which psychological differences between individual humans are due to genetic differences.
99% of the information contained in each human’s genome is uniform. This is the information that codes for species-wide traits such as bipedalism, front-facing eyes, and the brain’s core fight, freeze or freeze response to threatening stimuli.
The remaining 1% of each person’s genome contains the variable and always somewhat unique information that makes each of us distinct, one-off individuals.
The 99% makes us human (instead of, say, iguana or bonobo). The 1% makes you you (instead of, say, Mel Gibson, Jesus Christ or your classmate Simon).
Massive twin and adoption studies (with sample sizes reaching into the hundreds of thousands) have now conclusively demonstrated that genetic differences are the single largest systematic factor affecting personality differences between individuals.
What is ‘Heritability’?
‘Heritability’ refers to the extent to which individual differences in a trait are heritable. In other words, are inherited biologically; passed from parent to offspring in the form of genetic information. It measures how much of the differing levels of traits found between individuals can be attributed to genetic differences. Heritability is measured as a percentage of the entire detectable difference.
Heritability of psychological traits has been decisively shown to be, on average, 50%. This means that 50% of the difference in psychological traits between individuals is due to their genes. This is a massive influence! It dwarfs any other influence ever detected in psychological research. (Up until now the largest influences affecting differences in psychological traits have been able to account for between 1 and 5%, with 5% being considered very large!).
This makes genetics far and away the biggest single factor dictating differences in personality traits between individuals.
There is No ‘Gene For X’
A crucial point to understand is that there is no single gene for any trait. There is no gene for shyness, anxiety, happiness, aggression. There is no gene for baldness, weight gain, muscularity, or shoe size.
This “gene for x” canard has been used to distort the complex and nuanced findings of behavioral genetics, both by the field’s detractors (either when they simply fail to grasp the complexity of the findings, or when they deliberately ‘strawman’ the findings in an attempt to discredit them) and by special interest groups who want to forward their ideology (such as white supremacists).
How Do Genes Effect Personality?
The truth is that a trait is caused (or to be precise, made more probable) by a super-complex array of hundreds or thousands (or millions) of often tiny differences in the details of an individual’s genome.
Traits are predictable and detectable in genomes because scientists can now detect incredibly complex and detailed ‘weather systems’ in a person’s genome, made up of myriad single-nucleotide polymorphisms (SNPs) that each has a minuscule effect, but when taken in concert make a specific trait considerably more probable.
What Is Environment?
So if genetic differences account for, on average, 50% of the variability of traits between individuals, that leaves 50% that must be accounted for by some other cause.
Up until recently that 50% has been attributed to environment, also known as nurture.
The theory goes that the things that happen to an individual throughout their lives, and particularly in their early, formative years, and especially in their family life, have a profound effect on their personality. Freud brought this notion to the mainstream and it has been accepted dogma in most circles for much of the past 100 years.
The problem is that this idea has not been provable in any rigorous scientific studies. And, in fact, study after study after study has failed to demonstrate any clear link between family environment and personality.
This means that what the environment now refers to is everything that is not genetics. But what that ‘everything’ is, we do not know. ‘Everything’ now appears to mean the random hotch-potch of events and experiences that an individual has had in their life. But, crucially, it is not something that can be measured systemically. Because all hypothesized systemic influences, such as family, have been shown to have amazingly little detectable effect! These findings turn the field of psychology upside down!
The Nature Of Nurture
Not only this, but factors that were traditionally thought of as being 100% environmental have now turned out to show a considerable amount of heritability!
Friendship groups, parental interactions, whether we are read to as children, how much TV we watched, whether we get divorced, the quality of our social support systems…. all of these traditional measures of ‘environment’, which were thought of as acting upon us from the outside, have now been shown to be considerably affected (and predictable) by our genes.
Average heritability, across all environmental measures studied, has turned out to be a whopping 25% (and this includes highly un-heritable events such as ‘death of a loved one’, so heritability for more heritable ‘environmental’ measures such as friendship group, TV watching, and divorce are much higher than 25%).
We Create Our Environment
What happens to us affects us only to the extent that we perceive it to be ‘good’, ‘bad’, or ‘indifferent’. The same environmental force can act on two different people and affect them completely differently. It affects them differently because they have different, largely genetically influenced, personalities and ways of experiencing and incorporating the world around them.
People select environments that match their highly genetically influenced natural propensities and preferences. We are drawn to, and form friendship groups with, people who are genetically similar to us. People of high intelligence, on average, spend most of their time with other people of high intelligence. Sporty kids hang out with other sporty kids. Shy people are drawn to other shy people. Our friendship groups have a massive effect on us. But friendship groups are highly heritable. Our genes have a large effect on the friendship group we end up in.
People that tend to be ‘joyful, emotional, impulsive, engaged with life’ (all highly heritable personality traits) are more likely to get divorced. Divorce has always been viewed as a life event that acts on a person, but it turns out that that person’s genes probably had a large effect on whether divorce occurred in their life.
Whether we are naturally positive or negative, optimistic or pessimistic (all traits that show large genetic influence) determines how we perceive an endless array of ‘environmental’ effects, ranging from the weather, to our social status, to the quality of our social support network.
The Nature Of Nurture Implications
The nature of nurture is a fascinating and very exciting discovery. It is always thrilling to learn something new, cut away the dead wood of false and dogmatic ideas, and get closer to the truth. It is also exciting and potentially very helpful to know more about the truth of ourselves and society at large; what makes you you, and every other individual them.
Understanding the nature of nurture frees us from the unhelpful habit of learned helplessness. We can stop blaming our environments for who we are and how our lives have turned out, and instead start taking responsibility for creating the sort of environment that we believe suits us best and can help us to optimally florusrish, grow, and enjoy our lives.