Lower birth rates higher global population?!

05 Dec

It seems to me that there are competing headlines: global birth and fertility rates are dropping and that the population has just exceeded seven billion people and should reach nine billion by the year 2050.

It’s great that more women around the world are getting an education, which is wildly believed to be the biggest factor in the reduction in births.  More education leads to delayed childbirth plus higher health and exposure to birth control.  The birth rates in developed countries are much lower than in developing countries. But there are other factors that impact birth rates.  In the US, new data shows that the most recent recession is blamed for declining birth rates in almost every subsection of society.  Babies are expensive and women are waiting to have them until their financial situation improves, or is at least more stable.

A new CDC study found that birth rates for teens and women in their early 20s are the lowest since the 1940s. Rates fell 6 percent among women in their early 20s. The study also found there were 34.3 births per every 1,000 teenagers in 2010 – down 9 percent from 2009’s rates.

US birth peaked in 2007 with 4.3 million births.  In 2010 there were only 4 million babies born. The number of births pecked in 2007, but the number of babies per 1,000 people has declined since the baby boom, right after World War II.  This is explained by the fact that even though each person is having fewer children there are still more people of childbearing age.

If 1,000 women had 2.5 children then the next generation would have about 1,250 women.  If each of those women only had 2.2 children then there would be 1,375 women to have children in the next generation.


If 1,000 women had 2.5 children then the next generation would have 2,500 children.  If each of the women from the second generation only had 2.2 children then there would be 2,750 people in the next generation.

As you can see there are fewer people being born, but the size of the subsequent generation is still larger than the one before. This will continue to happen until the fertility rate drops below 2 children per female (one child to replace her and one child to replace her mate).

This explains the first reason that the world’s population is continuing to grow even as fertility rates decline. The second reason is that we are living longer.

In October a baby was born, it was the seven billionth person living on Earth right now.  If that baby was born in an industrialized country it is likely that the baby will live to be 100 years old.  Today the typical life span in these parts of the world is 80 years, which is 30 years longer than it would have been for a person living in 1910. The shortest global life span is 41-49 years in parts of sub-Saharan Africa.

National Geographic reports that on April 1, 2010 there were 53,364 people in the US over the age of 100.  That number is projected to reach 601,000 in 2050.

As people spend more time on earth, even if they have fewer children, the number will continue to increase. Let’s take the example above again.

If 1,000 women had 2.5 children at the age of 30, then the next generation would have about 2,500 people. At this point and time there are 3,500 people alive (parents and children).  Now 30 years later the 1,250 women born each have 2.2 children of their own and there are 6,250 people alive.    If each of the women in the second generation has 2.2 children then there will be 2,750 children in the next generation, which brings the population total to 9,000 people. At this point only 90 years has passed. Even with delayed child birth (a starting age of 30 for women) it is extremely plausible that grandparents and great-grandparents will be alive to see their grandchildren and great-grandchildren.  With longer life spans the mortality rate is lower and therefore the overall population can grow.

These are the two reasons (that I have found) to explain how we can have fewer children and still have a growing population.  It’s just growing slower and older.






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Posted by on December 5, 2011 in Uncategorized



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