In my Reason column last week, I wrote about Africa's economic prospects in view of the continent's explosive population growth. A number of readers wrote to me in response to the article and I will attempt to address their most important concerns below.

First, readers wondered if my population estimates reflected the expected changes to the total fertility rate (TFR) among African women. Indeed, they have. The population data in the original article came from the United Nation's database, which adjusts for different fertility rate scenarios.

Holding TFR constant, the world would contain 26 billion people in 2100. Of those, 16 billion would live in Africa. Contrast that with the "low" fertility variant, which estimates a global population of 7.3 billion (3 billion in Africa). In my article, I referenced the "medium" fertility variant, which assumes a global population of 11.2 billion and African population of 4.4 billion.

Second, a number of readers wanted to know how Africa's population can grow so fast, considering that it is economically so backward. In the past, economic output supplied a Malthusian check on population growth. That does not seem to be the case anymore. Why? I tried to answer that question elsewhere. Simply put, economic freedom (and, consequently, growth) benefits not only the people who have it, but also people who don't.

Consider a concrete example. Between 1960, the year of African independence, and 2015, the income gap between sub-Saharan Africa (SSA) and the United States has actually widened. In 1960, average GDP per person in SSA amounted to 6.31 percent of the same in the United States. Over the next 55 years, incomes in SSA adjusted for inflation grew by 55 percent. But they grew by 203 percent in America. That meant that in 2015, SSA amounted to 3.21 per cent of American income.

However, the gap in life expectancy, which is the best indicator of the overall standard of living, between the two has shrunk!

In 1960, SSA life expectancy was 58 percent that of the United States. Over the next 55 years, SSA life expectancy grew by 47 percent, while American life expectancy grew by 14 percent. So, in 2015, SSA life expectancy rose to 75 percent that of the United States.

To put it in terms of years, SSA life expectancy rose from 40.17 years to 59 years, while US life expectancy rose "only" from 69.77 years to 79.16 years.

Africans, in other words, did not have to become rich in order to start experiencing longer and better lives. Instead, all of Africa benefited from the technological advances that occurred elsewhere. The airplane, an American invention, flies life-saving medicines into the deepest Congo. Synthetic insulin, a Canadian invention, saves lives in South Africa. The photocopier, another American discovery, is making it easy for poor kids to learn how to read in Angola.

Third, assuming that a) the African population will grow as expected and b) economic conditions do not improve sufficiently to soak up all the additional workers, what will the future generations of Africans do?

The European TFR is well below replacement rate of 2.1 and the average age of Europeans is increasing. Already 17 percent of Europeans are over the age of 65. The African population, in contrast, is going to remain relatively "young" for decades to come.

In 2014, 84 out of 100 Africans had a cell phone and 20 out of 100 used the internet. It is unlikely that future generations of young Africans will want to sit around and see their lives wasted away in dysfunctional places like Niger or Burundi—when better alternatives are possible.

Whereas the United States is separated from Africa by a vast ocean, mass movement of people from Africa to Europe is relatively easy. So the obvious answer to the African conundrum seems to be immigration to Europe. If you like these statistics, please visit Human Progress.