History, 20th Century history 16 Humans 13 human 13 History, 21st Century 6 adult 5 female 5 male 5 Female 4 United States 4 Biological Evolution 3 Male 3 evolution 3 major clinical study 3 Adult 2 Animals 2 Article 2 Genetics, Population 2 History, 19th Century 2 Learning 2 Nutrition Surveys 2 Selection, Genetic 2 Socioeconomic Factors 2 animal 2 article 2 dental education 2 genetic selection 2 learning 2 legislation and jurisprudence 2 nutrition 2