"All social design is based on the size of the population, but also on the age structure, and it basically changes in a way we have not yet understood," said George Leeson, managing director of the BBC's Oxford Institute of Population Aging.
IHAT's Institute of Health Metrics and Evaluation (IHME) research at the University of Washington in Seattle has been published in The Lancet and compares public health in the world between 1950 and 2017.
Almost half of the world countries, mainly in Europe and North and South America, does not generate enough children to preserve the size of the population. Something that has significant consequences when communities get more "grandparents than grandchildren".
The result became "a big surprise" for researchers, writes BBC.
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Since 1950, childbirth in the world has almost halved: an average of 4.7 children per woman per 2.4 children per woman in 2017. But variations are great, the researchers write. In Africa and Asia, childbirth continues to grow in Niger on average for women who feed seven children during their lifetime.
According to IHME, Cyprus is the least fertile land in the world – a Cypriot middle-aged 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 of IHME, says that the most important element of population growth is education.
"If a woman educates herself, she will spend more school time, postpone pregnancies and therefore have fewer children," she says.
Mokdad says about it the populations of developing countries are still growing, so their general economies are common, which generally reduces birth over time.
"Countries are expected to improve economically, and more likely fertility is reduced and reduced.
The critical issue is when the average fertility rate of the country reaches 2.1 children per woman. Then childbirth begins to fall. When research began in 1950, no country was at this point.
"We have reached a watershed, where half of the countries have fertility levels below the level of compensation, so if nothing happens, the population will fall in these countries, which is a significant shift," says Professor Christopher Murray at IHME.
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The fact that birth rates are declining in many rich countries does not mean that the population also does so because the population of the country is a mix of childbirth, death and immigration. It may also last for a generation before the change begins to perceive, but as countries improve the economy, the phenomenon becomes more common by researchers.
We also live longer than ever before. Expected global life expectancy for men has increased from 71 to 48 in 1950. Women are expected to live up to 76 compared to 53 in 1950.
Heart disease is nowadays the most common cause of death globally, states IHME. Towards the end of 1990, newborn babies were born, followed by lung diseases and diarrhea.
"You see less mortality in infectious diseases when countries get richer, but also for other people with disabilities because people live longer," says Ali Mokdad.
He pointed out that although the number of deaths of infectious diseases such as malaria and tuberculosis has declined significantly since 1990, new non-communicable diseases have occurred.
– There are certain behaviors that lead to more cases of cardiovascular disease. Obesity is number one – it grows every year and behavior affects it, he says.
If development does not break, we have population development in a few children, but in very many age groups.
To combat the consequences of a diminishing population, three things can be done in the country, researchers say: Increasing immigration, women are raising children to political reform and raising retirement age.
However, none of the measures has been successful, but according to the study.
Countries with high levels of migration are faced with social and political challenges, but raising birth rates has not had a profound effect on fertile women, and demonstrations often refer to proposals for higher retirement age proposals.
Migration for young people poor countries move to rich countries, and it is not a solution to the global research.
George Leeson is still optimistic and believes that an aging population does not have to be a problem if it is adapted to society.
Population affects all our lives; traffic, how we live, consumption. It is about demographic development, but we have to plan the changed age structure in a way we have not yet understood, he told the BBC.
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