An adoption study is a research method in which genetically related family members who were adopted are compared with each other in order to tease apart genetic and environmental influences. Monozygotic twins are valuable research participants because they are genetically identical. When they are adopted by different families they are raised in different environments but still have the same genetic backgrounds. Researchers can surmise that common traits between the twins could be determined by genetics whereas differing traits could have been influenced by their environments. Some adopted twins who have been reunited as adults have been shown to have an astounding level of similarity.