"All social planning is based on population size, but also on the age structure and fundamentally changes in a way that we have not yet understood," said George Leeson, director general of the Oxford Institute of Population Aging at the BBC.
A study by the Institute for Metering and Health Assessment (IHME) at the University of Washington in Seattle was published in The Lancet magazine and compares public health in the world in the 1950s and 2017.
In almost half the world countries, mainly in Europe and North and South America, not enough children were born to maintain their population size. Something that will have serious consequences when communities gain more "grandparents than grandchildren."
The result was a "big surprise" for scientists, writes the BBC.
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From 1950, childbirth in the world decreased by almost half: from an average of 4.7 children per woman to 2.4 children per woman in 2017. The differences, however, are huge – scientists write. In Africa and Asia, childbirth continues to grow with the average women in Niger who feed seven children in their lifetime.
According to IHME, Cyprus is the least fertile country in the world – the average Cypriot woman gives birth to a child in her life. On the other hand, women in Mali, Chad and Afghanistan have on average more than six children.
Ali Mokdad, professor at IHME, says education is the most important factor in population growth.
"If a woman trains, she spends more time in school, puts off pregnancy and therefore she will have fewer children," he says.
Mokdad says that during populations in developing countries continue to grow, just as their economies generally grow, which usually has a smaller and smaller impact on labor over time.
"Countries are expected to become more economical, and fertility is more likely to diminish and even out.
The critical point is the average fertility rate in the country is 2.1 children per woman. Then the birth begins to fall. When the survey began in 1950, no country has reached this point.
"We have reached a breakthrough in which half of countries have fertility levels below the level of compensation, so if nothing happens, the population will decrease in these countries." This is an unusual transition, "says Professor Christopher Murray of IHME.
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The fact that the birth rate falls in many rich countries does not mean that the population does so because the population of a given country is a mixture of childbirth, death and immigration. This may take a whole generation before the change starts to notice, but as more and more countries will have better economies, this phenomenon will become more widespread, say the researchers.
We live longer than ever before. The expected global life expectancy of men increased to 71 years from 48 in 1950. Women are expected to live up to 76 years, compared to 53 in 1950.
Heart disease is out the most common cause of death in the world, IHME says. It was not until 1990 that neonatal problems appeared, followed by lung diseases and diarrhea.
"You see less mortality from infectious diseases when countries get richer, but also more disability because people are living longer," says Ali Mokdad.
He pointed out that although the number of deaths from infectious diseases such as malaria and tuberculosis has significantly decreased since 1990, new non-transmissible diseases have taken place.
– There are some behaviors that lead to more cases of cardiovascular disease and cancer. Obesity is number one – it increases every year, and our behavior contributes to this, he says.
If development is not interrupted, we will have population development with several children, but in very many centuries.
To counter the effects of the declining population, there are three things that a country can do, writes the researchers: Increasing immigration, making women feed more children political reforms and raise retirement age.
However, none of the funds was successful, says the study.
Countries with generous immigration are struggling with social and political challenges, and lockwork to increase the number of births has not had a major impact on fertile women, and proposals for a higher retirement age have often met with protests.
Migration to young people from poor countries are moving to rich countries, nor is it a global solution, according to the study.
George Leeson is still optimistic and believes that an aging population does not have to be a problem, as long as it is adapted to society.
Demography affects all parts of our lives; traffic, how we live, consumption. It's about demography, but we have to plan to change the age structure in a way that we have not understood yet, the BBC said.
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