References appear at the end of this appendix.
Since 1979, Professor Thomas Bouchard and colleagues have sought out twins from across the USA who were separated in childhood. On being identified, the twins undergo fifty hours of assessment, answering over fifteen thousand questions at Bouchard’s unit in the University of Minneapolis, Minnesota.
Through newspaper articles, books and television documentaries the Minnesota study has hugely influenced popular conceptions of the impact of genes upon behaviour. In most cases, these report seemingly astonishing similarities between twins who have never met each other. For example, the journalist Lawrence Wright (p. 45, Wright, 1997) writes of two of Bouchard’s twins who were separated at birth that they both liked their coffee black and cold, had both fallen down the stairs at the age of fifteen and had weak ankles as a result, at sixteen had both met the man they were to marry at a local dance, laughed more than anyone else they knew, and so on. Even Bouchard admits that such similarities are purely coincidental, but that has not stopped them from being endlessly purveyed as spooky evidence of genetics.
For a full critique of the scientific problems with the studies, it is worth reading the paper by Jay Joseph (2001). A fundamental concern is that Professor Bouchard told Lawrence Wright (p. 60, Wright, 1997) that he is not willing to release or allow for inspection by independent assessors the raw data on which his scientific papers are based. Given the history of fradulence in this field of research it is a particularly unfortunate refusal, and some scientists reject the validity of any of his findings until such an assessment is permitted. Suspicions about Bouchard’s genuine open-mindedness are compounded by the fact that in order to carry it out he has received grants to the value of $1.3 million from the Pioneer Fund of New York, which has its roots in the eugenics movement and which backs projects that advocate racial segregation (p. 50, Wright, 1997).
The published results contain several worrying and puzzling omissions in the data, serious absences of basic, vital information in the scientific reports from Bouchard’s group. Ideally for such a study, the twins would be separated at birth and given for adoption to parents who provide divergent child-rearing experiences. Yet average ages at which the twins were separated are often not provided. The amount of time that they have been in contact and the form that this has taken are not reported. In many cases the twins seem to have had extensive telephone contact before they visited Bouchard in Minnesota, which could have led them to convince themselves of their similarity.
Another issue is the parameters that Bouchard has studied. He has focused on ones most likely to provide support for genetic theories, such as IQ, but there is very little about the huge swathe of psychology which appears to have little or no heritability, such as choice of mate, violence and attachment patterns.
A fundamental problem is that the twins in his sample are nearly all self-selected. Following massive, nationwide publicity of the study in the media, in which similarities of twins were the focus, the twins usually contacted the researchers. This could easily mean that the twins in the study are motivated to identify themselves as similar to each other. There could be hundreds of other pairs who have not contacted him because they are convinced of their differences. What is more, it is possible that some of the twins have simply invented similarities in order to achieve media prominence and financial gain – several of the pairs have signed book and film deals.
Bouchard rejects calls for detailed case histories on the grounds that it would be a breach of confidentiality. Yet there is a long tradition of publication of full reports without any such problem being raised (Farber, 1981), and doubtless he could easily obtain permission if he felt this were necessary. The media need to adopt a more responsible attitude to the reporting of this study.
Farber, S.L., 1981,Identical Twins Reared Apart, New York: Basic Books.
Joseph, J., 2001, ‘Separated twins and the genetics of personality: a critique’, American J. of Psychology, 114, 1–30.
Wright, L., 1997, Twins, London: Weidenfeld and Nicolson.