Zero Degrees of Empathy: A new theory of human cruelty by Simon Baron-Cohen

Author:Simon Baron-Cohen [Baron-Cohen, Simon]
Language: eng
Format: azw3
ISBN: 9780718193348
Publisher: Penguin Books Ltd
Published: 2011-12-21T05:00:00+00:00

TWINS

If a trait or behaviour is even partly genetic, we should see its signature showing up in twins. The key comparison is between twins who are identical (monozygotic, or MZ) versus twins who are non-identical (dizygotic, or DZ). If the trait or behaviour in question does not differ much between MZ and DZ twins, then one is forced to conclude that genes play little if any role in the behaviour. This is because MZ and DZ twins are genetically quite different to each other: MZ twins are like genetic clones (they are genetically identical, so share 100 per cent of their genes), while DZ twins are genetically no different to any pair of siblings (they share on average 50 per cent of their genes). In contrast, MZ and DZ twins are environmentally quite similar to each other: they are the same age, typically growing up in the same family. Expressed differently, if you discover that the trait or behaviour in question shows a greater correlation among MZ twins than it does among DZ twins, then one can see that genes are at work.

Nearly all the studies of empathy in twins have found a greater correlation on empathy measures in MZ twins, compared to DZ twins.252–254 As an example, the heritability of affective empathy (i.e., how much of the variation in affective empathy is genetic) has been estimated from a twin study to be 68 per cent. That’s a lot. In contrast, one study looking at the heritability of ‘theory of mind’ (or cognitive empathy) found that MZ and DZ twins were quite similar,255 suggesting environmental rather than genetic factors predominate. However, this was challenged by a later study.256

Estimates of precisely how big the environmental and the genetic contributions to empathy are vary depending on how empathy is measured. For example, some twin studies use questionnaire measures, whereas others use observational measures. In studies of very young twins, observational measures include asking a mother to fake getting her finger caught closing a suitcase while her child’s reactions were filmed. Studies using this observational method among toddlers have shown a strong genetic component to empathy.257, 258 Observational methods are better measures of ‘affective empathy’ (the responsive component) and may be suggesting that of the two main components of empathy (cognitive versus affective empathy) there may be a larger genetic contribution in the affective component. The phenomenon of finding it difficult to reflect and report on one’s own feelings (alexithymia) also shows heritability from twin studies.259

Regarding Type Ps, a twin study that used the Psychopathic Personality Inventory (questionnaire) found specific scales (one called ‘Machiavellian egocentricity’, another called ‘cold-heartedness’) showed moderate heritability. In a UK study of twins, the callous and unemotional component of psychopathic tendencies at the age of seven showed even stronger heritability.260, 261 Twins are not the only ‘natural experiment’ to glimpse the importance of genes, since the same clues are also seen in studies of children who have been adopted, again pointing to ‘anti-social behaviour’ being heritable.262

Adoption represents another opportunity

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