In 1979, two identical twins living in Ohio who had been reared apart and had never previously met were reunited at the age of 39.
Their similarities in behaviour and life experience were uncanny.
According to press reports, they smoked the same brand of cigarette, suffered from tension headaches, vacationed on the same beach in Florida and had twice married women with the same first name (Linda and Betty).
Moreover, they had both worked in law enforcement and had the same hobby -- carpentry. Their sons' first names were James Alan and James Allan.
These remarkable twins inspired the Minnesota Study of Twins Reared Apart (MISTRA), which began in 1979 and lasted for 20 years.
MISTRA would ultimately examine 81 identical and 56 non-identical twin pairs who had been reared apart.
Studying twins who had been separated and raised in different environments provides an opportunity to determine the relative influence of heredity -- genes -- and environment on human behavioural and physical traits.
This chronological account of MISTRA is written by Nancy Segal, a psychology professor at California State University at Fullerton who was associated with MISTRA for nine years from 1982 to 1991.
Unfortunately, it is not really a book for a layperson. Its quantitative analyses may be digested by statisticians or geneticists but are dry for the ordinary reader.
Segal uses terms like "idiographic," "multiphasic," "discordant electrodermal habituation curves" and "probandwise concordance rates."
The main gist of her narrative is that MISTRA systematically and comprehensively tested twins for intelligence, personality, values, interests, religiosity, sexual orientation, mate choice, job satisfaction, sociality and health, and consistently found greater genetic than environmental influence on each measured trait.
These findings, as Segal says, "rattled the status quo within the psychological field."
From the 1930s to the 1970s, psychology was dominated by an environmentalist perspective, i.e., human behaviour was explained by forces outside the individual.
As a result of MISTRA and other studies, it is now widely accepted that genetic factors play a significant role in behaviour. Nature and nurture interact in complex ways.
The psychologists who conducted the MISTRA are on shaky ground when they attempt to incorporate testing for political attitudes.
They use the "Right-Wing Authoritarianism Scale" and the "Wilson-Patterson Conservatism Scale."
Why, one wonders, do they only test for attitudes associated with the political right? If "right-wing authoritarianism" is identified as a trait to be measured, shouldn't they also test for left-wing totalitarianism?
Perhaps the selective examination of political views was an attempt to appease the left, which had been a harsh critic of the twin study.
Segal has written an account that may be too technical to qualify as popular science, but she definitely conveys a sense of the groundbreaking nature of MISTRA.
Graeme Voyer is a Winnipeg writer.
Born Together -- Reared Apart
The Landmark Minnesota Twin Study
By Nancy L. Segal
Harvard University Press, 410 pages, US$50