Population of the world 10,000BCE-2100
By simply looking at the graph we can see that the population of the world grew by less in the first 11,900 years, than it has in the past fifty years. As we can see, growth until the year 1900 was very slow and steady compared to now, only reaching the first 100 million somewhere in the second millennium BCE, and the first billion in the early nineteenth century. To put that into perspective, the population grew by roughly one billion people every twelve years, between 1975 and 2011 (reaching four, five and six billion at each interval).
The old balance
The reason for this incredible change is due to the rapid decrease in infant and child mortality. Prior to then nineteenth century, the average life expectancy was at around 30, but without an explanation this number is very misleading. Before 1800, women had an average of six children in their lifetime, however four of these six children did not make it into adulthood, meaning that each mother had an average of (slightly more than) two children who would go on to reproduce, creating a balance in population growth. Before the nineteenth century, the life expectancy of somebody who reached adulthood was approximately fifty or sixty years.
The new balance
On average, since the 1800s, women have gradually been having less than six children in their lifetime, dropping to around 2.5 today. Although the number of children has dropped to less than half of what it was 200 years ago, the population is almost eight times larger than what it was back then. This is because we have more adults today than ever before, as humanity has brought the infant and child mortality rate to it's all time low. Today, there are approximately two billion children in the world (under 15), and scientists do not expect this number to increase by much in the next few centuries, instead population growth will occur as these children grow up, and the number of adults in the 30-45, 45-60 and 60-75 age brackets also grows to roughly two million each. The UN predicts that by 2100 the population will reach almost eleven billion people, where it will then begin to plateau, relatively similar to how it was in the first 11,000 years in this graph.
The old balance
The reason for this incredible change is due to the rapid decrease in infant and child mortality. Prior to then nineteenth century, the average life expectancy was at around 30, but without an explanation this number is very misleading. Before 1800, women had an average of six children in their lifetime, however four of these six children did not make it into adulthood, meaning that each mother had an average of (slightly more than) two children who would go on to reproduce, creating a balance in population growth. Before the nineteenth century, the life expectancy of somebody who reached adulthood was approximately fifty or sixty years.
The new balance
On average, since the 1800s, women have gradually been having less than six children in their lifetime, dropping to around 2.5 today. Although the number of children has dropped to less than half of what it was 200 years ago, the population is almost eight times larger than what it was back then. This is because we have more adults today than ever before, as humanity has brought the infant and child mortality rate to it's all time low. Today, there are approximately two billion children in the world (under 15), and scientists do not expect this number to increase by much in the next few centuries, instead population growth will occur as these children grow up, and the number of adults in the 30-45, 45-60 and 60-75 age brackets also grows to roughly two million each. The UN predicts that by 2100 the population will reach almost eleven billion people, where it will then begin to plateau, relatively similar to how it was in the first 11,000 years in this graph.
