Population on the earth is more than 7 billion. It has grown to this size over centuries. Population of earth grew slowly in early period. It is during last few hundred years’ population has increased at an alarming rate. The steam engine replaced human and animal energy. They provided mechanized, energy of water and wind. This increased agricultural and industrial production. Inoculation against epidemics and other communicable diseases, improvement in medical facilities and sanitation contributed to a rapid decline in death rates throughout the world.