Did infertility kill off the Neanderthals?

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Neanderthals may have gone extinct because the women of the ancient species slowly became infertile, researchers suggest. 

Scientists have yet to agree on a single reason explaining why they disappeared. 

Current theories focus on catastrophic events such as disease, warfare or climate change wiping them out, but there is little evidence supporting this. 

A researcher from France looked into the possibility it was instead due to decreasing fertility and investigated how much of an impact it would have on the long-term survival of the entire species.

Mathematical models revealed a decrease in fertility of just 2.7 per cent would see the species eradicated in 10,000 years. 

 

The research used computer models to predict how soon extinction came and was conducted by a team led by Anna Degioanni from Aix-Marseille University.

They looked at what would need to have changed in Neanderthal groups to see the population fall below 5,000 – which the study considered to be functionally extinct. 

It included female fertility, adult mortality and infant survival rates. 

They looked at what subtle changes would be needed to make them extinct in 4,000 years, 6,000 years and 10,000 years.

These time frames are considered by many scientists to be the most likely periods of time it took for Neanderthals to die out. 

Researchers primarily focused on female fertility and found a 2.7 per cent drop would be enough to make the species extinct in ten millennia.

But a five and eight per cent decline sped their demise up to just 6,000 and 4,000 years, respectively. 

The researchers write in the paper: ‘We show that, in the long run, a slight change in the fertility rate of younger females could have had a dramatic impact on the growth rate of Neanderthal metapopulation and thus on its long-term survival, in agreement with the observed extinction of Neanderthals within a 10,000, 6,000 or 4,000 years period’ 

A reason behind the decline is not stated by the researchers, but they tentatively suggest it would likely have originated from food scarcity.   

The authors add: ‘Because the amount of stored body fat influences fertility in women a decline in resources (caused by climate degredation or competition with sapiens) may affect fertility mostly for young women giving birth for the first time.’

The study was published in the journal PLOS ONE and also discovered infant survival rate would have to be decreased by just 0.4 per cent to send them extinct in 10,000 years.

A marginal increase to one per cent sees this jump enormously to just 6,000 years, showing how important survival of offspring was to Neanderthals. 

Like humans, they reproduced slowly and invested heavily in their children. other mammals have large litters to compensate for low survival rates but primates, and hominins especially, invest a large amount of resources in a few young. 

A further finding in the study was that if adult survival was slashed by ten per cent it would have a catastrophic impact on the species as a whole, causing almost instant extinction. 

Researchers suggest either disease from Homo sapiens or warfare a likely source of this sort of rapid decline. 

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