MADRID, XX (EUROPA PRESS)
En small populations, these random variations can wipe out entire family lineages. In the new study, researchers used mathematical models to examine how this demographic variability affects the survival of populations over many generations.
The study reveals that, due to random fluctuations in the number of births, a fertility rate of at least 2.7 children per woman is needed to prevent extinction with certainty, especially in small populations. However, a female-biased birth rate, with more females than males, reduces the risk of extinction, contributing to the survival of more lineages.
This perspective could help explain an evolutionary phenomenon observed for a long time: under extreme conditions such as wars, famines, or environmental disturbances, more females tend to be born than males. It also suggests that while extinction is not imminent in large developed populations, most family lineages will eventually disappear.
HAY QUE ESTABLECER TASAS DE FERTILIDAD OBJETIVO
Authors conclude that true population sustainability, as well as the sustainability of languages, cultural traditions, and various family lineages, requires rethinking conventional fertility goals.
The findings also have implications for conservation initiatives for endangered species, they point out.
«Considering the stochasticity in fertility and mortality rates, and in the sex ratio, a fertility rate higher than the standard replacement level is necessary to ensure the sustainability of our population,» they add.
