Twin studies and adoption studies are used to establish genetic arguments for the origins of human behavior. Twin studies compare identical twins who share 100% of their DNA to fraternal twins who share about 50% to determine if traits are inherited. Adoption studies compare adopted children to their biological and adoptive parents to isolate genetic influences from environmental factors. While these studies provide evidence that many traits have biological roots, they also have limitations such as twins and adopted children not representing all children and difficulties fully separating genetic and environmental influences.