Embryo Project Encyclopedia Articles

In 1990, Thomas J. Bouchard and his colleagues published the paper “Sources of Human Psychological Differences: The Minnesota Study of Twins Reared Apart” in Science Magazine. The paper described the results of a study initiated in 1979 on the development of twins raised in different environments. The scientists conducted their experiment at the University of Minnesota, in Minneapolis, Minnesota. The researchers physiologically and psychologically assessed monozygotic twins or triplets who were reared apart, comparing the similarity of those twins to twins who were reared together. The research team found that identical twins who are reared apart had the same chance of being similar as twins who were raised together. Bouchard and his colleagues concluded that genetic factors have a large influence on behavioral habits demonstrating the influence of the genetics on development.

In the article “The History of Twins, As a Criterion of the Relative Powers of Nature and Nurture,” Francis Galton describes his study of twins. Published in 1875 in Fraser’s Magazine in London, England, the article lays out Galton’s use of twins to examine and distinguish between the characteristics people have at birth and the characteristics they receive from the circumstances of life and experience. Galton calls those factors nature and nurture. Based on his study, Galton concluded that nature has a larger effect than nurture on development. By studying twins, Galton introduced a way to examine the effects of nature and nurture in people who were born with similar traits, which allowed him to focus on the effects of experience on a person’s development.

In 1916 Edwin B. Cragin in the United States published Conservatism in Obstetrics in which he discussed medical practices and techniques to preserve the vitality of pregnant women and their fetuses. Cragin argued that women who give birth via cesarean section, the surgical act of making an incision through both the abdomen and uterus to remove the fetus from a pregnant woman's womb, must rely on that method for future births. That claim was later coined the Dictum of Cragin. In Conservatism in Obstetrics, Cragin described obstetric techniques to maintain healthy births for women and fetuses. Cragin's article outlined the best practices for obstetricians in the early twentieth century, and publicized the claim that if a woman delivers a newborn via cesarean section, she should deliver any future newborn via the same method, a theory that persisted throughout the century.