Last week, Elon Musk claimed that “if people don’t have more children, civilisation is going to crumble,” and cited developed nations’ low and rapidly-declining birth rates.
In recent years, encouraging people to have more children has proved difficult in countries including Italy, Japan and Denmark.
As birthrates hit historic lows around the world, alongside well-reported economic and social issues, there are increasing concerns about what is impacting human fertility.
New research suggests that among other factors, air pollution from burning fossil fuels could play a significant role in the declining fertility levels seen in the modern era.
A study published in the journal Nature notes that “industrialised regions now have rates below levels required to sustain their populations”, and the researchers said their results show “reproductive health problems are partially linked to increasing human exposures to chemicals originating directly or indirectly from fossil fuels.”
Though the human population is the largest it has ever been, at 7.7 billion people, and with overall numbers still rising, a landmark study published in July in the Lancet, reported that across the world, fertility rates have almost halved, from 4.7 in 1950 to 2.4 in 2017.
The declining birth rate has been attributed to factors, including economic and behavioural elements, such as the changing role of women in society, improved access to healthcare and contraception, and fears over the worsening climate crisis.
But Professor Niels Erik Skakkebæk from the University of Copenhagen, Denmark, said that was not the whole picture.
He said: “We have to face it; environmental factors are having a decisive and negative impact on our reproductive capacity, and the cultural explanations cannot stand alone.
“Semen quality in healthy Danish men is today much poorer than 50 years ago. We have also seen a significant increase in testicular cancer in Denmark and the rest of the world.”
The study suggests that the decreasing birth rates began at the same time as industrialisation and the start of large-scale burning of fossil fuels.
The authors’ hypothesis is that fossil fuels are having a “major” negative impact on human reproductivity.
“Ten per cent of the entire global consumption of fossil fuels is currently used as ingredients in chemicals contained in more or less everything around us: Toys, clothes, cosmetics, food, packaging, building materials and so on,” said Professor Skakkebæk.
“Many of the substances are endocrine disruptors, and we are massively exposed to these substances, which can also be traced in blood, urine, semen and amniotic fluid from the entire population.”
The authors called for greater protections for pregnant women, and also suggested toxins in air pollution were having a range of negative impacts on unborn babies and young children.
Co-author of the study Professor Anders Juul said: “The foetus and children are particularly sensitive to chemical exposure, and this is a contributory factor to the significant increase in the number of congenital abnormalities of the male genital organs in infants, poorer semen quality in young men, and higher incidences of testicular cancer.”
“There’s no doubt that we’re facing a serious societal problem.”
He added: “It’s extremely important that we examine more closely the relationship between infertility and environmental factors.”
While there have been long-held concerns about the planet’s ability to support a rapidly growing and increasingly demanding species, there are also fears of what a collapsing population could entail.
This appears to be Mr Musk’s concern. He said: “So many people, including smart people, think that there are too many people in the world and think that the population is growing out of control. It’s completely the opposite. Please look at the numbers.“
As well as creating an ageing population, which will have to be supported by economically active young people, worsening fertility is forecast to take an extensive mental toll on individuals across societies.
The research is published in the journal Nature.