Fearless in the face of evidence

Why is it that some people hide away from challenge, while others are jumping from aeroplanes? "Fear in the face of the unfamiliar" is examined in Jerome Kagan's intriguing book Galen's Prophesy: Temperament in Human Nature.

As the title announces, Kagan's position resembles that of the ancient Greek physician, Galen of Pergamon, who was interested in the role of temperament in producing the melancholic and sanguine adult. Kagan presents us with interesting new evidence to show that human temperament can strongly influence the development of behavioural inhibition.

Kagan provides the reader with three sorts of evidence to argue that we inherit a biology which predisposes us to be fearless or fearful. From the first few months of life, 40 per cent of babies fail to show much reaction to novel stimuli, such as unfamiliar speech and colourful moving mobiles. At the other extreme, there are 20 per cent of young infants who are highly reactive, showing fretful behaviour and thrashing limb movements to these stimuli.

Such early classifications turn out to be powerful predictors of uninhibited/inhibited behaviour in later childhood. However, as Kagan uses different terms interchangeably, it is not clear whether he is claiming that early reactivity leads to fear or whether reactivity is an indication of fear itself.

The second source of evidence is the research showing the relation between sympathetic activity and fearless/fearful types of children. Kagan argues that heart rate and blood pressure are indirectly influenced by neurological structures involved in producing fear, of which the amygdala is believed to play the most prominent part.

Kagan is not surprised that such indirect measures are not nearly as reliable and stable as the overt behaviours. For this reason, he would have done better to have given the physiological evidence in a single section of the book, rather than in such a disjointed way. Then, the reader would get a more coherent picture of the possible underlying neurochemical pathways involved in fear and fearlessness.

The third type of evidence is given in an attempt to persuade the reader that inheritance is involved. We are told that the inhibited child is more likely to have blue eyes, a lean physique and a narrow facial morphology. Also, identical twins are reported to be more alike than fraternal twins in their levels of stranger anxiety.

Throughout the presentation of this evidence, Kagan is at pains to emphasise a qualitative distinction between the fearful and fearless type. This he does well, by showing that fearless children differ from those who are fearful in the nature of their reactive behaviours, heart rate patterns and fear characteristics, rather than one type of child having more or less of something compared with the other.

However, Kagan justifies his failure to discuss the possible effects of the interuterine environment on early fear reactions, by the fact that all the babies were born healthy and at full term. Yet, in using this reason, Kagan appears to be contradicting his claim that genetic differences should not imply natural inequalities and, by implication, that both timid and fearless behaviour alike can have an adaptive advantage.

Nevertheless, Kagan is wise to devote some space to accounting for why two fifths of his low and high reactives did not show the expected full-blown behaviours in later childhood. He cites a single study showing how an uninhibited child can be affected by early parental socialisation.

The effects of socialisation cannot be underestimated. Unfortunately, as all the children in Kagan's sample are middle class and Caucasian, he does not explore any potential economic and social influences. Birth order is mentioned as having a small interactive effect with gender and age in the development of fear. However, such crucial issues as family health, support and relationships are never discussed.

Despite these shortcomings, Kagan will, in my view, be successful in reaching both colleagues and interested non-specialist readers.

Kerry Sims is a researcher, Cognitive Development Unit, Medical Research Council, London.