Population movements have occurred throughout history. These migrations have differed with respect to destination and origin, source of motivation ("push" vs. "pull"), and characteristics of the migrant. For example, the transcontinental large scale movements of workers to the "new world" (Argentina, Australia, Brazil, North America) have been replaced by Interregional and often temporary migrations. In addition, whereas 18th and 19th century migrations were characterized by population movements from rich countries to those that were generally less developed, recent population flows originate in regions that tend to be poor and overpopulated and are destined for the more developed regions. Various regions of the world are characterized by an unskilled population exodus (e.g., from African countries to the oil-abundant Middle East), whereas others suffer from a severe brain drain (e.g., India).