Challenging the very core of psychology

Do our genes determine who we are? Does the environment have an independent impact on our development, or are so-called environmental effects actually reflective of the ways particular genes cause us to interact with the environment? Do parents and family 'matter' in child development? Or would an adopted child raised away from their biological family turn out much the same as if they had remained with their birth family? While advances in genetic testing allow behavioural geneticists to find likely groups of genes which may be associated with particular traits of human behaviour, the nature-nurture debate rumbles on.

One of the best-known researchers in Behavioural Genetics, Professor Robert Plomin (King's College, London), published his book Blueprint: How DNA Makes Us Who We Are last year. One of the headline assertions of the book is that parents make little difference to how children turn out, something which has surprised many in the world of psychology.

Writing for Psychology Today prior to the publication of his book last year, Plomin stated that genes contribute 'importantly to all the psychological differences between us' with inherited DNA accounting for roughly half of the differences in psychological traits including personality, cognitive ability and mental health. 

He goes on: 'The environment is responsible for the other half, but genetic research has shown that the environment does not work the way environmentalists thought it worked. For most of the 20th century, environmental influences were called nurture, because the family was thought to be crucial in determining environmentally who we become… Genetic research has shown that this is not the case. We would essentially be the same person if we had been adopted at birth and raised in a different family.'

Dr Naomi Fisher, a Chartered Psychologist writing for The Psychologist online, examined some of Plomin's claims. She writes: 'Reading Plomin's book as an applied psychologist, there is a sense of perhaps defensive disbelief… so much of what he writes runs counter to accepted psychological perspectives. Parenting and nurturing don't "make a difference"? Crucial environmental events in our lives are down to chance? This challenges the very core of psychology…'

Events we experience in our environment, Plomin says, are in part determined by our genes. In an email interview with Fisher he explained: 'Many experiences assessed on measures of life events, such as conflicts with others, don't just happen to us as hapless bystanders. Blueprint describes a new way of thinking about the environment, as experiences that we actively select, modify and create in part on the basis of our genetic tendencies.'

It may be hard for psychologists to accept that all human behavioural traits are heritable, but Fisher points out this idea, dubbed the Fist Law of Behavioural Genetics by Professor Eric Turkheimer, is uncontroversial in the field. 

She writes: 'Plomin argues that DNA is the only stable, systematic and long-lasting source of who we become – and that the environmental events which do make a difference are "unsystematic and unstable – in a word, chance". This is where the headline "Parents don't make a difference" comes from. He bases this on the absence of evidence for systematic effects of nurture, or in the terminology of behavioural genetics, "shared environment": that which is shared between children in the same family and which is assumed to make them similar.'

But Fisher poses the question: 'Parenting style and social economic status are counted as shared environmental factors. If they don't make a difference to what we become, then what does? Plomin's answer is chance or random events – but this feels unsatisfactory for many psychologists. Why would our brain respond differently (and in a more permanent way) to chance events than to many hours of nurture? How could this actually work?'

Scott Barry Kaufman, writing for Scientific American, outlines 12 of Plomin's statements, made in various publications since Blueprint was released, which he deems 'particularly problematic'. 

Kaufman, while excited about the progress being made in using DNA to predict traits, suggests caution: 'I firmly believe we need to be more thoughtful in determining what relevance these rapidly emerging findings have for the actual individual human beings who are inhabited by the DNA.' 

He goes on: 'What the evidence actually suggests is that families don't generally make siblings more similar to each other, or they only do to a small degree and only for specific traits. And to the degree that they do, those traits tend to diverge when children leave the home… But that's absolutely not the same as showing that family does not matter in terms of who we become. That conclusion simply does not follow logically from the scientific research.'

Emphasis within the field has shifted in recent years from finding 'the gene for…', to the calculation of 'polygenic risk' – predictive scores made up of thousands of genetic markers. When Fisher asked him, Plomin admitted that it was unlikely we would ever understand the mechanisms behind such scores. 

This is hard to swallow for some, with Fisher writing 'For applied psychologists, to think of polygenic scores as causal (as Plomin says they are) without understanding the pathway doesn't really make sense, because the pathways are what we work with.' Turkheimer added 'What do you do with your therapist? You sit there and try and reconstruct your nonshared environment.' And commenting on Twitter, neurogeneticist Kevin Mitchell said: 'not everything that matters can be measured' (to which we might add 'not everything that can be measured matters…).

It appears that the age-old 'nature-nurture' debate remains as complext and potentially divisive as ever. But surely if there is a 'blueprint', psychologists will remain in demand in terms of reading it, and mapping out how it unrolls across our lifespan.