Why can the study of twins be called gemellology?
D055592:Biophysical Phenomena; D001703:Biophysics; D001724:Birth Weight; D004200:Diseases in Twins; D005260:Female; D005826:Genetics, Medical; D006801:Humans; D007231:Infant, Newborn; D011247:Pregnancy; D012106:Research; D009626:Terminology as Topic; D014427:Twins; D014430:Twins, Monozygotic