For thousands of years the world's did not grow very much. People did not get very old because they did not have enough to eat. They also died of illnesses and . In the Middle Ages brought rats from Asia to Europe. They infected millions of people . The Black Death killed almost a third of the European population.

During the Industrial Revolution the population started to grow faster. Farmers could produce more food because they had . People had clean drinking water and doctors were able to give ill people to cure them. The of Europe started to live longer. Birth went up because fewer died right after birth. By the middle of the 20th century about 3 people lived on earth.

After that things started to change. In countries birth rates stayed high and the population continued to grow at a pace. In industrialized countries women were having fewer babies and slowed down. Today, Africa has the highest growth rate while Europe has the lowest.