The Great Pause Week 57: Mama at the Bat

"How do pandemics, climate variability, plastic, toxic pollution, and other threats affect fertility?"

 

Image after Saisha Bloom: beinG sLAVE

Some time back, I came across an odd fact that did not seem to reconcile with what had I thought about natural systems and planetary homeostasis. Girls all over the world, from the capital cities of Europe to the remote regions of Pakistan, were getting their periods younger. In Europe, menarche declined from age 17 in 1840 to about 13 in 1970. In North America it declined from about 15 in 1890 to 13 in 1920. The age of onset was shortening.

This extends the window of fertility, meaning women become able to bear more children during their lives. So why, if human overpopulation threatens all life on Earth, should that be “naturally” accelerating? 

One hypotheses is that since 1840, nutrition, average weight, and stress, have all changed markedly. Logically, an improved standard of living translates into begetting more children. Might it also be that we are genetically conditioned, by hundreds of thousands of years of extreme climate variability and other threats to our survival, to burst forth and flower when we luck into better conditions? We can observe, for instance, how the end of World War II brought a surge in baby-having, and how stresses from climate and culture are driving down fertility today. Nomadic refugees cannot easily accommodate childbearing and infant care. 

Another study suggests that vitamin D deficiency elevates risk of early menarche. Intuitively, this would correspond to a more outdoor lifestyle for children in 1840 compared to 1970. 

No datum directly shows that chemicals are responsible for the change. Data is accumulating, however, that environmental pollution may be affecting other factors. In 2017, Shanna Swan, an environmental and reproductive epidemiologist at Icahn School of Medicine at Mount Sinai in New York and her team of researchers completed a study that showed that over the past four decades, sperm levels among men in Western countries have dropped by more than 50 percent. They hypothesized that both lifestyle and chemical exposures may be the cause.

Count Down: How Our Modern World Is Threatening Sperm Counts, Altering Male and Female Reproductive Development, and Imperiling the Future of the Human Race

Count Down
Shanna H. Swan, PhD, is an award-winning scientist based at Mt. Sinai and one of the leading environmental and…www.simonandschuster.com

In the short span of a few decades, reduction in male fertility has overtaken the increase in female fertility and the extensions of average lifespan that were pushing population higher. Japan’s population has been in decline since 2006, creating problems as a greying population swamps pension and healthcare systems. It’s a similar story in South Korea, Italy, Spain, and across most of Eastern Europe. In only four industrialized countries are women, on average, having the two children required to sustain population size.

“It’s too early to be alarmist,” says Henri Leridon, who heads the Laboratory of Epidemiology, Demography, and Social Sciences at the University of Paris XI. On the lifestyle side of the equation, many factors converge to lower fertility:

• Women in Western countries have been electing to have children later, which is bound to result in fewer children per family. 
• The expansion of in vitro fertilization may have created a cohort of adults who have inherited their parents’ fertility problems.
• The shift towards having more sexual partners post-adolescence has increased sexually transmitted diseases, including Chlamydia trachomatis, a major cause of female infertility which is rarely diagnosed and produces no obvious symptoms.
• Up to ten percent of US women are thought to have infertility related to obesity, where eggs do not mature or there is a failure to ovulate.
• Smoking, alcohol consumption and a range of other lifestyle factors can all reduce a couple’s ability to conceive, usually affecting women more severely than men. 

On the chemical exposures causality, researchers have reported:

• A woman’s stock of eggs is defined by the number and maturity of her ovarian follicles when she herself was an embryo. Normal fetal follicular development depends on the mother’s diet and other lifestyle factors, including her exposure to chemicals.
• Adult male sperm count and quality is determined largely by the development of sperm-nurturing Sertoli cells in the embryonic testes. This depends heavily on exposure to sex hormones in the womb, which again is influenced by the mother’s lifestyle and other environmental factors.

Where global fertility stands now is hard to say. For example, among 1,540 British couples aged 16–59, taking longer than one year to get pregnant fell from 21% in 1960–65 to just 10% in 1991–93. Fertility was rising. Yet, in a survey of thousands of USAnian couples, fertility declined between the early 1980s and the mid-1990s.

Swann thinks the US trend is the more likely to dominate in the future. Her team found that sperm counts have dropped almost 60% since 1973 and could reach zero by 2045. 

Zero. Let that sink in. That would mean no babies. No reproduction. No more humans. Forgive me for asking: why isn’t the UN calling an emergency meeting on this right now?

 — Erin Brockovich 

Swann writes, “The current state of reproductive affairs can’t continue much longer without threatening human survival. It’s a global existential crisis.” 

Writing for The Guardian on March 18, Erin Brockovich observed:

In the United States today, for example, you can’t eat the deer meat caught in in Oscoda, Michigan, as the health department there issued a “do not eat” advisory for deer caught near the former Air Force base because of staggeringly high PFOS levels .… 

***

The chemicals to blame for this crisis are found in everything from plastic containers and food wrapping, to waterproof clothes and fragrances in cleaning products, to soaps and shampoos, to electronics and carpeting. Some of them, called PFAS, are known as “forever chemicals”, because they don’t breakdown in the environment or the human body. They just accumulate and accumulate — doing more and more damage, minute by minute, hour by hour, day by day. Now, it seems, humanity is reaching a breaking point.

***

The European Union, for example, has restricted several phthalates in toys and sets limits on phthalates considered “reprotoxic” — meaning they harm the human reproductive capacities — in food production.

I suspect life on Earth would be considerably better, not just for humans but for all other creatures, if human population crashed to, say, one billion. What fertility alarmists seem to worry about is the economy.

But we have been here before.

References

Butler, D. The fertility riddle. Nature 432, 38–39 (2004). 03 November 2004

Flaws, Jodi A., Fady I. Sharara, Ellen K. Silbergeld, and Anne N. Hirshfield, “Environmental exposures and women’s reproductive health” in Women and Health, pp. 625–633. Academic Press, 2000

Pal, Lubna, and Hugh S. Taylor. “Role in Reproductive Biology and Reproductive Dysfunction in Women” in Vitamin D, pp. 783–795. Academic Press, 2018.

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The COVID-19 pandemic has destroyed lives, livelihoods, and economies. But it has not slowed down climate change, which presents an existential threat to all life, humans included. The warnings could not be stronger: temperatures and fires are breaking records, greenhouse gas levels keep climbing, sea level is rising, and natural disasters are upsizing.

As the world confronts the pandemic and emerges into recovery, there is growing recognition that the recovery must be a pathway to a new carbon economy, one that goes beyond zero emissions and runs the industrial carbon cycle backwards — taking CO2 from the atmosphere and ocean, turning it into coal and oil, and burying it in the ground. The triple bottom line of this new economy is antifragility, regeneration, and resilience.

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“There are the good tipping points, the tipping points in public consciousness when it comes to addressing this crisis, and I think we are very close to that.”

 — Climate Scientist Michael Mann, January 13, 2021.