# The Demographic Time Bomb, by James Rickards

Demographics will be economic destiny. From James Rickards at dailyreckoning.com:

The reason humans are dying out is simple and straightforward. It’s best summarized in the famous line from Walt Kelly’s 1970 Pogo cartoon: “We have met the enemy and he is us.”

Humans are the reason humans are dying out. We’re not having enough babies. It’s that simple.

When I use the word “enough” it’s important to put a mathematical value on that. This is not guesswork. The key number is 2.1. That refers to 2.1 children per couple, known as the replacement rate. The replacement rate is the number of children each couple must have on average to maintain global population at a constant level.

A birth rate of 1.8 is below the replacement rate of 2.1. This means your population is declining. It may be aging also as the existing population lives longer and new births neither replace the dying nor lower the median age.

A birth rate of 4.1 is well above the replacement rate. This means your population is expanding and your median age is falling even as individuals live longer. Behavior is complex, but the math is really that simple. The replacement rate of 2.1 is the dividing line between population growth and decline.

Why isn’t the replacement rate 2.0? If two people have two children doesn’t that maintain the population at a constant level? The answer is no because of infant mortality and other premature deaths.

If a couple has two children and one dies before reaching adulthood, then only one child can contribute to future population growth as an adult. A birth rate of 2.1 makes up for this factor and contributes two adult children per two adult parents.