Earth has been in the middle of a population boom since about the 1960s. It took until about 1800 for the first billion people and now we add a billion about every 12-14 years. We're so good at making more humans we're fighting to slow down population growth, but this is a very recent thing in human history. How did that happen?
Passed Year Billions
- 1800 1
127 1927 2
33 1960 3
14 1974 4
13 1987 5
12 1999 6
12 2011 7
14 2025* 8
18 2043* 9
40 2083* 10
The basic equation is deceptively simple: increase birth rates, decrease death rates. But it's not quite that simple. And it's more important to decrease death rates, and when they die. This is all about increasing the fertility of the population. You do that by...
Decreasing child mortality.
It doesn't matter how many people are born if they die before they become adults and have kids of their own. In the Middle Ages this was anywhere from 30 to 50%. In 1915 in the US infant mortality was at 10%. Now the worldwide average is more like 5%.
Decreasing maternal mortality.
Historically, childbirth is one of the most dangerous things a woman can do. In the Middle Ages the cause of death for a woman would be child birth, or associated complications and infections, about 20% of the time. In the US in 1900 this was still high at 1%. In some parts of the world today it's still at 15%. Since the number of women is the limiting factor, it decreases your breeding population if they're dying during birth. Now, in the US, it's practically 0.
The risk of a woman dying as a result of pregnancy or childbirth during her lifetime is about one in six in the poorest parts of the world compared with about one in 30 000 in Northern Europe.
Source: "Maternal mortality: who, when, where, and why"
The single biggest cause of death is being poor. It decreases your access to medical care. It reduces the amount and quality of food you have. It increases stresses on your body, the amount of toxins you're taking in, and so on. Child mortality rates are 2 to 3 times higher in the developing world than the developed world.
Increasing the food supply everywhere.
Can't have kids if you can't feed them. Gotta feed all those people. More food means cheaper food means more calories for everyone. More calories means healthier people having healthier babies who will live to have healthy babies.
Part of our current population boom, and abundance of food, is due to the Green Revolution. The development of cheap, industrially produced fertilizers and pesticides, plus changes to how we manage our crops and what crops we were growing, in the early 20th century saw a huge increase in farm productivity in rich nations who had the money and industrial capacity to support it. Later in the 1930s to 1960s a concerted effort was made to make the same technology available world wide. The result was a huge boom in the global food supply.
When everything had to be done by hand, people traditionally had big families with lots of children because they needed a lot of people to work the farm. Someone has to feed animals, milk the cows, plant the crops, til the soil, mend the fences, go to town, shoe the horses, etc... etc... etc... The more children you had the more land you could work. The more land you could work the more crops and animals you could grow and sell. People will naturally want bigger families.
Once you industrialize you have machines for all that. You need less people. You have smaller families. The birth rate drops.
Having a Prolonged Period of Peace.
The unprecedented era of world peace (nothing on the scale of the world wars), global cooperation, and trade we've enjoyed since 1945 added to the population boom.
Modern war means sending your young generation are soldiering, not working or having children. It means diverting your food and industrial output towards warfare. It means wrecking your infrastructure. This all leads to a lowered standard of living for the civil population. Less food, less prosperity, less young people of breeding age, this all means lowered birth rates, and higher child mortality rates.