The world's population is increasing all the time because more people are being born than are dying. The population of the world can be changed by other causes such as extinction level events, and natural and un-natural disasters (e.g., earthquakes, war). In January 2012, the United Nations said the Earth's population had reached 7 billion.
- YAN Kun(2011). The tendency equation of the population and its limit value in the United Kingdom (Brief annotation of the connection equation(R)), Xi'an: Xi'an Modern Nonlinear Science Applying Institute.