Population trends are caused by three categories of trends: natural growth (affected by fertility and infant mortality), migration (immigrants in minus emigrants out), and death (affected by life expectancies, aging, disease and disaster).
1. Fertility is declining globally, heading toward replacement levels. This simply means that women are having fewer children. Although we continue to add more people in the world, population growth seems to be inexorably heading toward maintenance levels. The trend is fairly easy to identify: comparing the ratio of girls to boys in school versus the total fertility rate for the period 1960-2009, you can see that as girls become more prevalent in school, the fertility rate falls. Most of the high-population countries have already seen their population fertility rates fall under 3 births per woman. Managing total population growth is all about figuring out what the “replacement level” is for a population and getting as close to that as possible: it will vary, depending on the situation, but is typically between 2 and 3 babies per family. Very small shifts can lead to population aging or robust population growth. However, at this point the only top-30 population countries with fertility rates above 3 per woman are Sudan, Pakistan, Tanzania and the Democratic Republic of Congo.
2. Infant mortality is declining globally as health improves. Since more children are surviving past the age of 5 and into childhood and youth, this means a natural increase in the population–many poorer nations used to have a lot more babies but infant mortality was very high, so the net population growth was lower. It also means that the population has begun to age a bit because once children are past the age of five the odds of their surviving into older age is higher.
3. Globally increasing life expectancy. In the 1960s, the world was dramatically divided between those countries with a life expectancy under about 50 years, and those with a life expectancy nearing 70. In the mix of the “top 30 countries,” only a small handful were in the latter category, and they were mostly Western: the United States, the UK, Italy, Germany, Ukraine, Spain, Argentina, and Japan. The remainder had life expectancies under 50 years. Indeed, many were closer to 40: Nigeria, the Dem. Repub. of the Congo, and Indonesia are examples. As the past half-century progressed, however, remarkable progress was made in raising the life expectancy. By the early 1990s the situation had all but reversed: the only countries with life expectancies lower than about 60 were Bangladesh, Sudan, Tanzania, Nigeria and the Congo. Today, the three holdouts are the Congo (wracked by war), Nigeria, and—in a stunning reversal—South Africa, which has been deeply scarred by the impact of HIV/AIDS.
1. Emigation: when people move out. There are a number of regions where the level of emigration is of course quite high–places where resources are low, food insecurity is high, and war or violence are constant threats. The recent drought in the Horn of Africa has sent thousands of people daily from Somalia into Kenya’s Dadaab refugee camp–one of the largest in the world. Emigration early on saps the nation of its highest-resource people: when a country becomes unstable, the people with the most resources, connections, and education tend to see it coming early on and are most able to leave. This “brain-drain” however can spark a downward spiral in the nation, robbing it of needed resources and capable business and government leaders. If things become really bad, then a mass exodus can occur as people try to get out of the country–such an exodus can cause dramatic upheavals.
2. Immigrants: when people move in. Populations can be increased by people moving into a new place. Views on immigration are, of course, very mixed. The natural-born citizens can look with disdain on immigrants coming in. The culture of a place can be dramatically changed when the ethnic mix is changed. Immigrant “ghettos” can be created–places within a culture where the majority language is not spoken at all. Despite our many negative views about immigrants, however, we need to recognize God has demonstrated a heart for the immigrant, that many (if not most) of the heroes of our faith were wanderers, immigrants, exiles, nomads, refugees, and even illegals for most of their lives, and that immigrants can bring many positive things to a place. For example, much of the church growth in Europe can be attributed to Christian immigrants (especially Africans): immigrants from Africa or Asia are far more likely to be Christians than any other religion.
1. Death: by any cause. Finally, on the “other side” of the population equation, we must not forget that people die. In some places the death rate has fallen very low, but among many unevangelized peoples of the world it remains quite high. Lifespans are unmercifully short. Disease, disasters and violence are all common in places where the blessing of the Gospel has not been brought–and while we can say that Godless heathens treat each other horribly, perhaps we should begin by considering the root cause of their Godlessness. All too often it is not a choice on their part–but rather a choice of ours.