original_query: What is the assumption regarding the demographic transition and its spread to less developed countries?
query: What is the assumption regarding the demographic transition and its spread to less developed countries?
answer: The United Nations Population Fund estimates that human population may peak in the late 21st century rather than continuing to grow until it exhausts available resources, based on the assumption that the demographic transition is spreading from developed to less developed countries.  This is corroborated by recent research, except for Sub-Saharan Africa.