A new study published in the journal Scientific Reports shows that falling birth rates from the 1800s to the 1900s played a direct role in women living longer over that same time period.
Today, women have an average lifespan longer than men, but that wasn’t always the case.
In the study, researchers analyzed more than 140,000 individuals from the Utah Population Database to reveal men who were born in the early to mid-19th century lived on average two years longer than women. During this period, fertility within the population lowered from an average of 8.5 children in the early 1800s to an average of 4.2 children per woman in the early 1900s.
The researchers also saw female lifespan go up during the study period, while male lifespan continued to be mostly stable, supporting the theory that differential costs of reproduction in the two sexes result in the moving patterns of sex differences in lifespan across human populations.
Paying a price for children
The information revealed that only women paid a price of reproduction in the form of reduced remaining lifespan after the reproductive period. Women who delivered 15 children or more lived an average of 6 years shorter than women who gave birth one time. There was no connection between quantity of children fathered and life expectancy in males.
Popular theories have said each individual has finite resources that can be devoted to reproduction on the one hand and restoration of the body on the other hand. This indicates that decreased reproduction ought to benefit female lifespan when women pay greater costs of reproduction than men.
“This illustrates the importance of considering biological factors when elucidating the causes of shifting mortality patterns in human populations,” Elisabeth Bolund, postdoctoral research fellow at Uppsala University, said in a news release. “Our results have implications for demographic forecasts, because fertility patterns and expected lifespans are continuously changing throughout the world. For example, the results suggest that as more and more countries throughout the world go through the demographic transition, the overall sex differences in lifespan may increase.”
The reasons supporting sex-based variations in lifespan are a major topic of debate. While females commonly live longer than men, this is much less pronounced in societies ahead of the demographic changeover to lower mortality and fertility rates.
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