It seems like every time I take a look at Facebook one of my friends is annoucing they're pregnant or they just had a baby. You would never guess that fertility rates have been falling drastically over the past 100 years, but they have!
Fertility rates in the US have dramatically decreased throughout the past century.
This is quantified with a number called the TFR (Total Fertility Rate). The TFR is based upon the fertility rates of women in age specific categories during their 'child bearing years'. This traditionally constitutes ages 15-44 or 15-49. This number represents the average number of children a woman would birth throughout the life span of her fertility. In other words, if the average woman in a particular geographic area would birth 3 children in her life, the TFR would be 3.
In order to maintain the current population of any given area, the TFR would have to be roughly 2.1 (2.06 exactly). The US government has been keeping track of this data since 1909. Upon their initial assessment, the TFR was approximately around 3.5; however, this number has fluctuaded over the past 100 years during particular time period.
We dropped to around 2.25 during the Great Depression, understandably so, but hit a peak of 3.7 in the 1960s. Unfortunately, since the 1970s, we have mostly been below the 2.1 average that we would need to maintain our population. Furthermore, this is a global issue and not just local to the US.
Since the 1970s China's birth rate has dropped an astonishing 71%!
China, Russia, Brazil, Japan, Canada, Australia and all of Europe with exception to Turkey, France and Ireland have ALL dropped below the TFR levels required to maintain their current populations. Predictions state that the global population, if we maintain this current course, will actually start decreasing by the end of the 21st century.
According to a study performed in 1992, male sperm count has decreased by more than half since World War 2. This drastic drop off was noticed by analyzing data within just a 10 year period. That's 50% less fertility in males in just 10 years! Strangely enough, a study showed that male testicles have been decreasing in weight simultaneously. Some estimates believe that sperm counts will drop below 20 million per milliliter within our life time. This would effectively render the male population sterile!
Why has this number dropped so drastically? Much to the chagrin of scientists, there is no absolute answer to this question just yet. There are a few theories in the works, however.
To be continued...