Nature, nurture: mind the trap

Issue section: 
Issue: 
(406)

Is it the DNA we are born with or our environment that determines how we act? John Parrington, author of The Deeper Genome, looks beyond this false dichotomy to a dialectical approach.

Imagine if someone invented a portable supercomputer that required only the wattage of a light bulb to run, but had the literary imagination of a William Shakespeare or Emily Brontë, the scientific genius of an Albert Einstein or Marie Curie, and the musical talent of an Amadeus Mozart or Billie Holliday. In fact such a computer already exists — it’s called the human brain.

Of course, the brains listed above belonged to some particularly gifted individuals. But that doesn’t mean the rest of us should underplay the power of our own cerebral capacities. Our native language that we learned as toddlers, our ability to eat using a knife and fork, kick a football, dance to music or drive a car — these “ordinary” skills elude the most powerful artificial computer.

The critical feature that distinguishes the human brain from such computers — but also that of all other animal species on the planet — is our brain’s capacity for self-conscious awareness. It is that which underlies our language capacity, tool-using skills, ability to plan ahead in space and time, and our powers of imagination.

Yet one thing that continues to elude modern science is what makes this amazing organ tick. This lack of understanding is not only a problem for our awareness of how our bodies work, but also because, for all its amazing powers, the human brain seems very susceptible to going wrong. Or at least that’s what recent figures from the UK Mental Health Foundation indicate. These show that about one in four adults in Britain experiences a diagnosable mental disorder in a given year.

Of course, one might wonder what type of “illness” affects so many people, and indeed some experts criticise what they see as increasing over-medicalisation of individuals lying within the spectrum of normal human behaviour. So Peter Kinderman, head of Liverpool University’s Institute of Psychology, recently said, “Many people who are shy, bereaved, eccentric, or have unconventional romantic lives will suddenly find themselves labelled as mentally ill. It’s not humane, it’s not scientific, and it won’t help decide what help a person needs.”

This is particularly a concern given the increasing diagnoses of children with conditions like “attention deficit and hyperactivity disorder”, or “disruptive mood dysregulation disorder”. Critics argue that this is not only inappropriate labelling since such children may simply be bored or naturally boisterous, but also dangerous, since such conditions are increasingly treated with drugs whose long-term effects on the brain are far from clear.

Drugs

Despite such concerns, it would be a mistake to underestimate the misery caused by serious conditions such as schizophrenia, major depression, or bipolar disorder — which affect around one in 17 of the British population. Yet the drugs available to treat such disorders remain blunt-edged tools, whose mechanism of action is far from clear. Indeed, some critics believe that such drugs are little more than “chemical straitjackets”, that suppress extreme psychotic symptoms, but leave patients feeling like “zombies” with their mental capacities dulled and their emotions blunted.

Clearly, effective diagnosis and treatment of mental disorders requires a proper understanding of human brain biology. The challenge here is to make sense of an organ that — with its 100 billion nerve cells joined by 100 trillion connections — is the most complex object in the known universe. At the same time, comprehending the human mind cannot only be a question of biological understanding, since human beings are unique in being part of a complex social network.

In fact Marxists argue that current human society is historically specific, being characterised by particular means and relations of production — capitalism — that distinguish it from past societies. Moreover, a key dynamic in the current capitalist society is the class struggle between the mass of workers and the tiny minority who run society. Importantly, Marxists see people in capitalist society as alienated from their work and themselves, particularly the exploited class, workers, but also the rulers themselves. Finally, the particular balance of class forces will impact upon individual consciousness.

On the biological front, there is much to be excited about in terms of current neuroscience. Although the mouse brain has a thousand times fewer nerve cells than that of a human, there are many structural and functional similarities between the two structures. And new developments in ways to genetically label specific nerve cells with different colour fluorescent tags are making it possible to construct a precise structural and functional map of all the nerve connections in a mouse brain.

Most remarkably, the new field of optogenetics involves manipulating the activities of individual nerve cells in a genetically engineered mouse by beams of precisely directed laser light. This functional dissection of brain activity is providing important information about the nerve impulses that underlie Parkinson’s disease tremors, pain, and epilepsy. In addition, this approach has been used to manipulate memory, both to overcome amnesia and cure depression in a mouse model, with potentially important implications for future treatment of similar human disorders.

Importantly, such studies are challenging previous overly simplistic views of how brains function. So Feng Zhang of the Massachusetts Institute of Technology believes that “traditionally when we think about developing drugs to treat brain diseases, it’s all about this hypothesis that there’s some kind of chemical imbalance. But that’s a very gross and inaccurate way of thinking about how the brain functions.

“What optogenetics is starting to highlight is that abnormal signalling between different cells in specific neural circuits is probably underlying many of the neurological or psychiatric diseases.” And Zhang believes that a better understanding of such neural circuitry could lead to the development of more precise drug treatments.

While animal studies are providing new insights into brain function, ultimately we need to understand how all this relates to what is going on in a self-conscious human brain, both in normal circumstances and during disorders of the mind. Importantly, while uncovering the complex molecular and cellular structure of the brain is a necessary starting point for understanding how our minds work, we will also require a philosophical approach that can make sense of such complexity. And here a dialectical approach to the mind has much to offer.

An important aspect of this approach as applied to an object like the human brain is its avoidance of the twin perils of biological and social reductionism. Biological reductionism is the view expressed by James Watson, the co-discoverer of the DNA double helix structure, when he said, following the completion of the Human Genome Project, that “we used to think our fate was in the stars. Now we know, in large measure, it is in our genes.”

Such a view was echoed by Daniel Koshland, editor of the prestigious Science magazine, who said that the genome findings would rapidly reveal the molecular basis for “illnesses such as manic depression, Alzheimer’s, schizophrenia, and heart disease”. Such claims were based on the idea that common mental disorders would have a simple genetic basis, with defects in a few key genes defining the particular disorder, and thereby representing targets for new drugs to treat it.

In fact the problem has not been a failure to identify links between mental disorders like schizophrenia and bipolar disorder and specific genetic differences between individuals, but rather the bewildering number of these. So a recent study found more than 120 regions of the human genome that were different in schizophrenic individuals compared with unaffected ones.

Such findings make a mockery of the idea of a “schizophrenia gene”. However, given that a much clearer link with two genes associated with energy metabolism emerged from a recent study of depression, it seems to me unwise to discount the possibility of genetic tendencies to mental disorder. Importantly, this latter study, led by Jonathan Flint of Oxford University, did not study depression as a whole but only the most severe form, known as melancholia.

Symptoms

Flint believes his study succeeded where previous attempts had failed precisely because it focused on this very specific form, and that the practice of lumping mental disorders together into broad categories may be masking real differences between what are actually quite distinct pathological conditions. This may fit with the fact that an individual can be classified as schizophrenic or depressive by having one set of symptoms while another has a completely different set.

One problem with many scientific discussions of mental disorders is that they place far too little emphasis on the social basis of such conditions. Yet a 2006 study showed that black people of African Caribbean origin in Britain are nine times as likely to be diagnosed as schizophrenic as white Britons. And the difference isn’t genetic — reported schizophrenia levels among black people living in the Caribbean are the same as among whites in Britain.

The exact reason for such differences remains to be established but it seems likely that the experience of racism, and the psychological pressures this may cause, could be an important factor, as could racist attitudes among health professionals who diagnose this disorder.

A similar demonstration of the link between social factors and depression was shown by a study by George Brown and Tirril Harris in 1978. This found that working class women were much more likely to succumb to this condition than more affluent women, which Brown and Harris linked to the impact of “more severe life events”, and greater difficulties with finance and housing.

Unfortunately, recognition of the importance of social factors in mental “illness” can sometimes spill over into another form of reductionism, which sees biological factors as having no role to play in disorders of the mind. Such social reductionism, which is a central feature of so-called “behaviourist” psychology, treats the individual as a blank slate upon which the environment makes its mark.

This view of the mind was encapsulated by behavourism’s founder John Watson, who in 1930 said, “Give me a dozen healthy infants…and I’ll guarantee to take any one at random and train him to become any type of specialist I might select — doctor, lawyer, artist, merchant-chief and, yes, even beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race.”

In fact this viewpoint, particularly as developed by Watson’s follower B F Skinner, lent itself to some reactionary conclusions, such as espousal of the value of a society where “conditioned” individuals blindly obey the dictates of their leaders, as satirised in Aldous Huxley’s novel Brave New World, and dangerously close to the realities of Nazi Germany or Stalinist Russia.

A fundamental flaw with this viewpoint is that it downplays the very real way in which individual differences in specific abilities, personality and temperament — all potentially affected by our biology as well as our social environment — shape the unique way each one of us responds to life’s challenges and opportunities.

Challenge

This is particularly an issue given that the new science of “epigenetics” has recently uncovered evidence that the human genome may be far more directly susceptible to the effects of the environment than previously suspected. Such findings challenge the standard view that the genome only changes very gradually through the accumulation of changes in the DNA code.

One study last year showed that stress in early life can have profound effects upon the human genome. Daniel Notterman of Pennsylvania State University examined two sets of nine year old boys, one being children who had grown up in a poor and stressful environment, the other boys from more privileged backgrounds. Notterman found that in some of the boys in the stressful environment the tips of the chromosomes — the 23 units that make up our genomes — were significantly shortened, by up to 40 percent.

Given that the shortening of chromosomes has been linked to ageing and susceptibility to disease, these are worrying findings. However, an intriguing aspect of the study was that only a subset of the boys in the stressful environment were so affected, and this was linked to slight biological differences in their production of the brain chemicals dopamine and serotonin. Although these chemicals mediate human characteristics like love, happiness, self-confidence and motivation, abnormalities in their actions in the brain are associated with depression, bipolar disorder and schizophrenia.

This study suggests that the link between stress and the epigenome is a complicated one, and may explain why although stressful environments may trigger mental disorders, biological differences may also affect which individuals succumb.

It’s particularly important to recognise the complexity of this relationship in the light of a recent study by Rachel Yehuda at New York’s Mount Sinai Hospital, which found that some Holocaust survivors, but also their children, show epigenetic alterations in their genomes linked to their experience in the Nazi concentration camps.

Importantly, all the evidence points to people being no more determined by their environment than they are by their genes. Instead it is the interaction between our unique biological make-up as individuals, and the opportunities and challenges that society throws at us, that affects our progress in life.

And while the experience of the Holocaust has been associated with an increased risk of stress disorders that may be passed down to future generations, one of the most inspiring political figures I’ve ever had the fortune to listen to was Leon Greenman. He survived Auschwitz, but rather than let the experience determine his life in a negative way, he became a tireless and effective campaigner against Nazi groups in Britain under the slogan “Never again”.

Most importantly, whatever genetic and epigenetic differences mark us out as individuals, the past experience of different revolutions shows that, in circumstances of mass struggle, there is empowerment and unlocking of individual potential on a similarly mass scale. Because of this, I look forward to the day when a future socialist society has not only created new scientific ways of treating mental disorders with a precision undreamt of today, but perhaps no longer needs to, because of the enriching effect of such a democratic society run by the majority, not just the richest 1 percent, upon the human psyche.