In 2002, after applying for government assistance in the state of Washington, Lydia Fairchild was told that her two children were not a genetic match with her and that therefore, biologically, she could not be their mother. Researchers later determined that the genetic mismatch was due to chimerism, a condition in which two genetically distinct cell lines are present in one body. The state accused Fairchild of fraud and filed a lawsuit against her. Following evidence from another case of chimerism documented in The New England Journal of Medicine in a woman named Karen Keegan, Fairchild was able to secure legal counsel and establish evidence of her biological maternity. A cervical swab eventually revealed Fairchild’s second distinct cell line, showing that she had not genetically matched her children because she was a chimera. Fairchild’s case was one of the first public accounts of chimerism and has been used as an example in subsequent discussions about the validity and reliability of DNA evidence in legal proceedings within the United States.

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.