Humanity will disgust? 2.1 a child per woman is not enough to survive

So that the population of people in the long term does not extinct, there should be at least 2.7 children in a global bill for one woman. This is a much larger fertility rate than previously assumed – according to new analyzes published in “PLOS One”.

According to the definition, the fertility rate means the number of children that an average woman would give birth throughout the end of the reproductive period (15-49 years), assuming that in individual phases of this period she would give birth with an intensity observed in the examined year, i.e. by the adoption of partial fertility coefficients from this period as unchanging.

It is often assumed that the fertility rate of 2.1 per woman guarantees the level of replacement necessary to maintain the population. This number, however, does not take into account random differences in the number of children, as well as mortality rates, gender proportions and the likelihood that some adults will never have children – note scientists from Japan and the Philippines in Plos One.

Researchers point out that Within small populations, such variability can contribute to the disappearance of entire families.

As part of the new study, scientists used mathematical models to examine how such demographic variability affects the survival of the population in the perspective of many generations.

The authors of the study found that – as a result of sudden fluctuations in the number of births – a fertility rate of at least 2.7 child per one woman is necessary to guarantee survival (or in other words: avoid extinction) especially small populations. In other words, to ensure the survival of the human population in the long run, women should give at least 2.7 children during their lives.

The risk of extinction of the population decreases when the proportion of newborns changes in a certain way: when more girls are born than boys. Such a change helps to survive in the long run of a larger line of families.

Conclusions from the analyzes in “PLOS One” can be helpful in explaining the evolutionary phenomenon observed for a long time: the fact that In difficult conditions – e.g. in the case of war, hunger or environmental disorders – more girls usually are born than boys.

It also allows you to think that while extinction of large, well -developed populations is not inevitable, most of the family lines will eventually disappear.

The authors of the publication come to the conclusion that The real “maintenance” of the population (similar to languages, cultural traditions or diverse family lines) requires rethinking of traditionally understood fertility goals. These discoveries are also important for attempts to protect endangered species in which target fertility indicators are determined. (PAP)

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