A Summary of Human Population Growth and Future Options


The birth rate in the US in 1910 was 31.1/1000 population per year or 0.0311 (USstats.htm). The UN estimated a birth rate in Sub-Saharan Africa in 1950-55 of 49.1/1000 or 0.0491 (UN Birth rates.htm). If I assume that the maximum average birth rate for humans has always been about 50/1000 or 0.0500 and that the average net population growth rate was 1.0002 (0.02%/year) between 1 AD and 1250 AD (World Population Growth.htm) then since:


Net growth rate = 1 + births deaths

Then: 1.0002 = 1 + 0.0500 death rate

Or: death rate +1.0002 = 1 + .0500

Or: death rate = 1.0500 -1.0002 = 0.0498


Thus, throughout most of human history, birth rates have only slightly exceeded death rates and the human population grew very slowly. The death rate did not begin to decline much until the inventions of soap, clean drinking water, and sewage systems during the scientific revolutions of 1700 to 1950. By 1970, the human population growth rate had increased to 1.0203 or 2.03% per year (Doubling time = T2 = log(2)/log(net growth rate) = log(2)/log(1.0203) = 35.5 years.). The doubling time from 1 AD to 1250 AD was about 3,000 years!


The US CIA in 2006 estimated 8.25 births/1000 (1.39 births/woman) in Germany and 47.35 births/1000 (6.71 births/woman) in Uganda on average (CIA births.htm). High birth rates are correlated with low incomes per person in poorly developed countries.


Note that 50 births per 1000 population per year corresponds to about 7 live births per woman on average although the range is at least 0 to 15 live births per woman. A population will increase anytime births exceed deaths or when births per woman exceed about 2.0. A population will decrease only when the birth rate is lower than the death rate. The human population explosion since the invention of soap, clean drinking water, and sewage systems after the discovery of bacteria has been driven by a Stone Age birth rate of up to 50/1000 and a declining death rate.


If the average birth rate never drops below 2/woman, the human population will try to approach 15 billion, but starvation and disease will probably increase the death rate and keep the maximum between 9 and 12 billion (World2.htm). There are many better alternatives as indicated by Heaven.htm and World_model.htm. All better outcomes require that we reduce the world average birth rate to 10 to 15/1000 (depending upon average life expectancy) fast enough to maintain, and hopefully increase, the average income per person (GDP/capita) while converting from fossil fuels to nuclear fusion and renewable energy sources.


Many people are hoping for an infinite frontier where the human population can grow forever and find infinite cheap resources. This is why many support the space program. The evidence for other habitable planets so far is not at all promising. Even if we could find one other planet similar to Earth, we could never send enough people there to make any difference in the population on Earth Space.htm.

Our real problem is to maintain a stable human population on Earth with a reasonably high GDP per capita and a reasonable distribution of incomes. Future energy sources, costs, and energy efficiency will determine what GDP we can maintain. GDP per capita will then be determined by the size of the human population. Since we will burn all fossil fuel reserves by about 2100 at current rates of use (last line at Fossil Fuel Reserves.htm), we have about 100 years to plan for and make a major transition in energy sources and related population policies.

The infinite frontier is only an illusion which we seek at great peril.