Culture evolution is the major factor responsible for population increase. Early in human development, people invented tools to hunt animals. Later they built shelters to protect themselves. Step by step, they made life easier. As a result, fewer died from natural forces, such as harsh climate and disease.

　　In the past, when population grew, there was unexplored territory to inhabit. But now, almost all the habitable land has been explored.

　　The world’s population may reach 8.7 billion in 2033. It is clear that world population is a serious issue that needs careful attention. Human beings are unique to solve problems through cultural evolution.(发展） Facing the world population explosion in the near future. We must carry out the birth control program in order to save the mankind and save the world.