Introduction: Science and social knowledge – The new genetics and the beginnings of eugenics – Eugenics in Latin America: Its origins and institutional ecology – Racial poisons and the politics of heredity in Latin America in the 1920s – “Matrimonial eugenics”: Gender and the construction of negative eugenics – National identities and racial transformations – U.S., Pan American, and Latin visions of eugenics – Conclusion: Science and the politics of interpretation.