As discussed above, the planet's population has grown rapidly during the last couple of decades – and even though population growth has been slowed down in certain areas by the decrease in the birth rate, the planet's population still continues to grow. This is due to the fact that even more young adults are able to form families and produce children. This development will slow down only during the course of the next couple of decades. This phenomenon can be studied using the concept of the fertility rate.

The fertility rate describes the number of children that a woman between the ages of 15 and 49 will give birth to on average. The total fertility rate of our planet has steadily declined from 3,4 to 2,5. This means that women on Earth give birth to approximately 2,5 children on average. In some developing countries, the fertility rate has decreased from 6 to 3, but continues to be extremely high in some areas. In Europe, the fertility rate is just under 2, whereas in Africa it is around 5. Some of the highest fertility rates in the world are in African countries: for example, the fertility rate of Niger is 7,6.

Africa is the continent with the highest fertility rate in the world. 

Fertility rate by country. Almost all European countries have a fertility rate below two. This means that, on average, European women give birth to under two children during their lifespan.

Population growth is also increased by the decrease in the global mortality rate. Access to basic health care and hygiene, as well as to advances in medicine, have all helped to decrease the mortality rate of the planet. These advancements have made it possible to protect people from diseases and treat people back to health when illness strikes. Infant mortality has also decreased as vaccines have become more effective. This also results in a lower birth rate, as people do not have to produce as many children to guarantee their own survival.

HIV was previously thought to have a drastic effect on population growth, but its influence has been lower than expected. This is despite the fact that even 25 % of the populations of some African countries are affected by the virus. The effect of wars on population growth has likewise been relatively small.