Increasingly after World War II, aid was justified as a contribution toward lowering the fertility rate and thus halting population growth. During the 1930s, demographers compared industrialized and third world countries and drew conclusions that morphed into a cause-and-effect model that guided development aid. Known as the demographic transition model, Cuba experienced a baby boom when Fidel Castro displaced Fulgencio Batista, in 1959. Castro explicitly promised a redistribution of wealth and, according to the demographers S. Diaz-Briquets and L. Perez, fertility rose in response. Cross-cultural and historical data suggest that people have usually limited their families to a size consistent with living comfortably in stable communities. Stakeholders to consider when evaluating mass immigration include the immigrants themselves, various socioeconomic sectors in the receiving countries, and those remaining in the developing countries that migrants leave. This chapter suggests that those remaining will be harmed because emigration stimulates fertility.