"All social plans are based on age structure as well as population size, and fundamentally change in ways we have not yet understood." George Leeson, CEO of the Oxford Population Aging Institute (BBC) I said.
A study by the Institute of Health Assessment and Evaluation (IHME) at the University of Seattle, Washington, was published in The Lancet and compares public health worldwide between 1950 and 2017.
In almost half of the world There are not enough children in Europe, North America and Latin America to maintain the population size. It will have important consequences when the community has more grandparents than grandchildren.
The result writes, as the "great surprise" for the researchers, the BBC.
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Since 1950, births in the world have almost halved. That is, an average of 4.7 to 2.4 per woman by 2017. But the variation is big. In Africa and Asia, childbirth continues to increase with the average women in Niger, who are feeding seven children throughout their lives.
According to IHME, Cyprus is the most fertile country in the world. The average woman in Cyprus is giving birth to a lifetime child. On the other hand, the average number of women in Mali, Chad and Afghanistan is more than six.
Professor Ali Mokdad of IHME says education is the most important factor for population growth.
"When a woman takes a train, she spends more time at school and defer pregnancy, so she has fewer children."
Moodard As the population of developing countries continues to increase, the economy is generally on the rise, which generally reduces the impact on births over time.
"The country is expected to be financially better, and the fertility rate is likely to decline and level out.
It is important to note that the average birth rate for a country is 2.1 children per woman. Then the birth starts to decrease. When the study began in 1950, no country had reached that point.
"In half of the countries, we have reached a watershed where the level of fertility is below the level of compensation, so if nothing happens, the population will decrease," says Professor Christopher Murray of IHME.
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The fact that birth rates are falling in many developed countries does not mean that the population will do so because of the mix of birth, death and immigration. It may take a generation before change starts to become noticeable, but researchers say that as more economies improve, the phenomenon becomes more common.
We also live longer than before. The life expectancy of men increased from 71 to 48 years old in 1950. The woman is expected to live in the age of 76 in 1950 compared with 53 now.
I have heart disease these days. The most common cause of death worldwide is IHME. At the end of 1990, there was a neonatal problem followed by lung disease and diarrhea.
"People live longer, so as the country gets richer, the death toll from the epidemic decreases, but more disabilities occur," says Ali Mokdad.
He noted that deaths from infectious diseases such as malaria and tuberculosis have declined significantly since 1990, but no new epidemic has occurred.
There are certain behaviors that cause more cases of cardiovascular disease and cancer. Obesity is number one, increasing every year and our actions contribute to it.
If development is not interrupted, we will develop a small number of children and populations of many ages.
Researchers pointed out that immigration increases, women are fed more children through political reforms, and raise retirement age.
But no action succeeded, the study said.
Countries with generous immigration suffer from social and political problems, locks to increase fertility do not have a significant impact on fertile women, and proposals for retirement age often met with protests.
Young people, According to this study, poor countries can not migrate to rich countries or become world class solutions.
George Leeson is still optimistic, and I do not think it needs to be a problem if the aging population adapts to society.
Demography affects every part of our lives. Transportation, how we live, consumption. It's all about demographics, but he told the BBC that we had to plan a changed age structure in a way we did not yet understand.
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