Recent research indicates that smaller population sizes and random variations in birth rates increase the fertility threshold required to prevent extinction.
A new study published in the open-access journal PLOS One suggests that human populations may need a fertility rate of at least 2.7 children per woman to reliably avoid long-term extinction, significantly higher than the commonly cited replacement level of 2.1. The research was led by Takuya Okabe of Shizuoka University, Japan.
Although a fertility rate of 2.1 is typically viewed as sufficient to maintain population size, this standard estimate does not consider several important factors. These include random fluctuations in the number of children individuals have, mortality rates, sex ratios, and the possibility that some adults may never reproduce. In smaller populations, these stochastic variations can result in the loss of entire family lines.
To explore the long-term consequences of such demographic randomness, the researchers developed mathematical models that simulate population dynamics across generations. Their findings reveal that higher fertility rates are necessary to buffer against these inherent uncertainties and ensure population survival over time.
Female-Biased Birth Ratios Offer Protective Effects
The study found that, due to random fluctuations in birth numbers, a fertility rate of at least 2.7 children per woman is needed to reliably avoid eventual extinction – especially in small populations. However, a female-biased birth ratio, with more females than males born, reduces the extinction risk, helping more lineages survive over time.
This insight may help explain a long-observed evolutionary phenomenon: under severe conditions – such as war, famine, or environmental disruption – more females tend to be born than males. It also suggests that, while extinction isn’t imminent in large developed populations, most family lineages will eventually fade out.
In stark contrast to the newly suggested sustainability threshold of 2.7 children per woman, global fertility rates have been steadily declining for decades. According to the United Nations, the global average fertility rate in 2024 was approximately 2.3 and is projected to drop below 2.1 by mid-century.
The authors conclude that true population sustainability – as well as the sustainability of languages, cultural traditions, and diverse family lineages – requires rethinking conventional fertility targets. The findings also have implications for conservation efforts of endangered species in which target fertility rates are set, they point out.
Diane Carmeliza N. Cuaresma adds, “Considering stochasticity in fertility and mortality rates, and sex ratios, a fertility rate higher than the standard replacement level is necessary to ensure sustainability of our population.”
Reference: “Threshold fertility for the avoidance of extinction under critical conditions” by Diane Carmeliza N. Cuaresma, Hiromu Ito, Hiroaki Arima, Jin Yoshimura, Satoru Morita and Takuya Okabe, 30 April 2025, PLOS ONE.
DOI: 10.1371/journal.pone.0322174
Funding: Japan Society for the Promotion of Science (JSPS) KAKENHI grant nos. 23KK0210 and 21H01575 (HI), 21K21115 (HA), 21K03387 (SM), and 21K12047 (TO)
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9 Comments
We have too many humans on this planet as it is. A natural decline in population is good news.
Yay!!!!! This is the first REALLY good news I’ve heard in a long time. Human population collapse. Oh, music to my ears, and to the ears of polar bears, whales, dolphins, chimpanzees, gorillas, pandas, wolves, lions, tigers, bears, rhinos, birds, butterflies, bees, trees, coral, etc. etc. I just hope this collapse comes in time for them. With over 8 billion of us, I’m still very worried it won’t happen soon enough.
This is actually good news. It’s not gonna be a “collapse”. “Collapse” is a catastrophic scenario deliberately pushed by the likes of Elon Musk.
A reduction in the population is good for the environment, good for the exploitation of the remaining resources and it’s ultimately good for our relationship to our economy.
A constant growth is desired only because someone needs to “pay for the retirees” – and that’s a one way street to a disaster. A timely degrowth will give us time to find more sustainable ways of living in this civilization.
Only for a suicidal lot infected with the woke mind virus, removing themselves from the gene pool.
Luckily conservatives are still having babies.
iWhat are they gonna feed them with, you braindead MAGA worm?
Plenty of food after the lefty loons check-out, taking their globalist power masters with them. Remember, farmers are majority conservative. We know how to grow things. Always did. Always will.
As soon as I get a car you are getting another cake.
The pathetic cheers of a murderous, liberal waste.
Jennifer, you are right in that humanity is rapidly destroying earth and its inhabitants. But a simple decrease in human population won’t do. This is because the destruction is wrought by only a few, and I suspect those few are well connected enough to survive.