An examination of fundamental assumptions of the twin method.
D005260:Female; D005787:Gene Frequency; D005821:Genetic Techniques; D014644:Genetic Variation; D005823:Genetics; D006801:Humans; D011247:Pregnancy; D012107:Research Design; D012931:Social Environment; D014427:Twins; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic