Until the 1600's human population remained rather stable, with approximately ½ billion people world-wide.

Since that time, global human population has undergone rapid growth, standing at nearly 6 billion today.

Human population now doubles every 40 years.

By 2150, human population size will likely range between 8-15 billion people.

Currently, humans use ¼ of global primary production (land and sea) for our own purposes.  It is unclear that we can harvest much more of this production without severe consequences.

Is it inevitable that human populations will outstrip global carrying capacity?

Population change in Europe

• Before 1600, birth and death rates were equal but high (approximately 35 per 1000 people per year).
• Through the development of modern medicine by 1650, death rates began falling.  By 1850, death rates were approximately 20 per 1000, but birth rates remained at 40 per 1000
• Beginning in 1900, birth rates underwent a rapid decline as well.  Today, both birth and death rates range around 12 per 1000.
• During the 400 years it took for birth and death rates to equalize, the number of European people increased rapidly, leading to the colonial settlement of the western hemisphere, Africa, Asia.  In 1800's 1/5 of total population migrated to other regions.
• Over time, Europe progressed from high birth-high death to high birth-low death to low birth-low death rate

The Demographic Transition

• This change from high birth and death rates to low birth and death rates have also been seen in other countries.
• Only in industrialized countries, however, has low birth and death rates been achieved.
• If the global population can pass through this transition to low birth and death rates more rapidly than Europe, it is possible for the global population to not outstrip the Earth's carrying capacity.
• Thus, we need to understand WHY this transition takes place.

Mechanisms Underlying the Demographic Transition

• When death rates are high, birth rates are also often high to compensate, as parents want at least 2 children to survive to help care for them in old age.
• When death rates fall, the attitudes which contributed to high birth rates do not change as quickly.
• Over time, couples often do choose to have fewer children.  If you know that all will live, then only conceive as many as you want to raise.
• The factors which lead to this change include:
  • Changing economics.  
    • In preindustrial agrarian society, the more children, the more workers, and the more family wealth.
    • In industrial society, more children mean more cost, and less wealth.
  • Changing status of women.  When female worth is based upon her ability to conceive, many children will be born.
    • As women achieve higher education, jobs, and status separate from reproduction, women will choose to do other things with their life.
    • This mimics the high status of women in early society, in which women and men were equal participants.  In these societies, birth rates were kept low by women, as they were busy doing other things.