Overpopulation is a generally undesirable condition where an organism's numbers exceed the carrying capacity of its habitat. The term often refers to the relationship between the human population and its environment, the Earth, or smaller geographical areas such as countries. Overpopulation can result from an increase in births, a decline in mortality rates, an increase in immigration, or an unsustainable biome and depletion of resources. It is possible for very sparsely populated areas to be overpopulated if the area has a meager or non-existent capability to sustain life (e.g. a desert). The population has been growing continuously since the end of the Black Death, around the year 1400, although the most significant increase has been in the last 50 years, mainly due to medical advancements and increases in agricultural productivity.
Contributions by Dacoutts, User2004, and Ultramarine.