The Importance of Shared Environment in Mother-Infant Attachment Security: A Behavioral Genetic Study
Bokhorst and colleagues studied a hundred and fifty-seven pairs of identical and non-identical twins to separate genetic from environmental influences on infant attachment. The result is unusual in behavioural genetics, where genes normally account for a substantial share of almost everything measured. Here they accounted for essentially none of the difference between secure and insecure attachment, and none of the difference in disorganised attachment. What explained security was the environment shared by twins in the same family, accounting for around half the variance, with the remainder attributable to unique experience and measurement error. The same study found the opposite pattern for temperament: genes explained the large majority of differences in how reactive an infant was. And temperamental reactivity did not predict whether twins shared an attachment classification. So attachment and temperament behave as separate things, and attachment looks like a property of the relationship rather than of the child.
Bokhorst and colleagues studied a hundred and fifty-seven pairs of identical and non-identical twins to separate genetic from environmental influences on infant attachment. The result is unusual in behavioural genetics, where genes normally account for a substantial share of almost everything measured. Here they accounted for essentially none of the difference between secure and insecure attachment, and none of the difference in disorganised attachment. What explained security was the environment shared by twins in the same family, accounting for around half the variance, with the remainder attributable to unique experience and measurement error. The same study found the opposite pattern for temperament: genes explained the large majority of differences in how reactive an infant was. And temperamental reactivity did not predict whether twins shared an attachment classification. So attachment and temperament behave as separate things, and attachment looks like a property of the relationship rather than of the child.
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Bokhorst, C. L., Bakermans-Kranenburg, M. J., Fearon, R. M. P., van IJzendoorn, M. H., Fonagy, P., & Schuengel, C. (2003). 'The importance of shared environment in mother-infant attachment security: a behavioral genetic study.' Child Development, 74(6), 1769-1782. Shared environment about 52 per cent of variance, heritability effectively zero. Replicated in a nationally representative sample of 485 same-sex twin pairs: Roisman, G. I., & Fraley, R. C. (2008), Developmental Psychology, 44(3), 831-839.
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- What the Crib Actually Decides, Why We Care
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https://doi.org/10.1046/j.1467-8624.2003.00637.x
DOI: 10.1046/j.1467-8624.2003.00637.x