Peter Gluckman: Mixed cues confuse young brains

Opinion

In biology we distinguish between why and how particular events happen.

In approaching issues of teenage crime, New Zealand's alarmingly high rate of teen pregnancy (the second highest in the Western World), schoolyard bullying and youth suicide, alcohol and drug abuse, we should reflect on the biological basis of behaviour.

That is, how the human brain functions within a social context. This might suggest new ways of approaching a problem for which the "band-aid" of societal constraint is clearly failing.

The human brain was designed for an environment very different from ours today. Comparing the size of the human brain with those of other primates suggests that we evolved to live in social groups of no more than 150 people.

In fact, research shows this is roughly the number of people most humans are comfortable with and until 10,000 years ago no humans lived in larger social groups.

The marvel of human biology is our capacity to adapt to different environments. But never before in our history has our environment changed so rapidly.

Just as many have not adapted to fast food and develop diabetes, it is now clear much of what we label behavioural disorder is the result of living in an environment our brains are simply not designed for.

Technological advances over the last generation have made society infinitely more complex and placed enormous pressures on the human brain. We now have thousands of interactions each year.

Many - particularly via electronic media - do not involve direct contact, yet have an emotional impact and stretch the capacity of our brains to adapt. Nowhere are these pressures more intense than for our young people.

Adolescence is a new phenomenon: the past 200 years has seen the age at which girls in Northern Europe complete puberty fall from an average age of 17 to about 12 - and it appears similar for boys.

This is largely due to better nutrition for mothers and children coupled with improved child health.

But if we define adolescence as the period between biological maturation and acceptance as an adult, then adolescence has stretched from an interval of one to two years to more than a decade in less than 100 years.

During this period the brain is subject to mature hormonal influences, yet it appears unable to cope.

We can think of the social brain as receiving hormonally driven inputs that encourage risky behaviour but counterbalanced by a control system which allows mature individuals to evaluate the consequences of an action, such as inappropriate sexual behaviour or stealing, before doing it.

Over the last five years we have discovered the pathways of the brain which confer wisdom, judgment and impulse control are not fully mature until an average age of 19.

Has this always been the case? If it has, the implication is that the last components of maturation were less important in simpler societies.

However, it may be that brain maturation now takes longer either due to our greater social complexity or because the rate of maturation has been slowed by society's overprotective attitude towards childhood.

Our societal mores, expectations and education systems derive from times 50 and more years ago when adolescence represented a far shorter time-span.

Society has further compounded the problem through the ambiguous, hedonistic messages of media and marketing that seek to exploit this gap between the maturation of body and brain.

We urgently need to reduce this gap. We have learnt, first in rats and most recently in humans, that stressful events in early life can permanently alter the way genes work in the brain. This is a naturally evolved process.

If early inputs predict a risky world, then survival is more likely if one has a shorter attention span, is more aggressive and more anxious. People living in stressful environments are more likely to have children whose behaviours fit such environments rather than our societal norms.

Sadly, we know poverty is one of the most potent stresses on families and examples of intergenerational cycles of disadvantage abound.

We also know from overseas studies that children who go through earlier physical puberty are more at risk - five times the rate of suicide in boys, much higher rates of eating and mental health disorders in girls and drug abuse and antisocial behaviour in both.

Modern society is hard to grow up in, overprotecting on the one hand while encouraging risk on the other. Clearly, we must break the cycles of disadvantage, but will that be enough?

What can we do to accelerate brain maturation? Should we gradually increase the responsibility we give young children or do adolescents need a more structured environment in which to mature?

We have an immense challenge. The biological conundrum is real and we must strive to provide a safe environment for young brains to mature in.

* Professor Gluckman is director of the Liggins Institute, University of Auckland, a leading centre for research on fetal and child health, breast cancer, epigenetics and evolutionary medicine.