Male Births Declining as Global Temperatures Rise

Fertility rates worldwide have been falling and a growing body of research is showing that male births are particularly at risk, potentially due to climate change trends. Data has been collected from around the world for decades, and trends are revealing themselves in a concerning way.

Male Births are More Common than Female Births?

After much hype in the last half of the 20th century about world “overpopulation” – and for good reason as the population has grown by over a billion since then – the first couple of decades of this century have seeing fertility rates falling. According to Robert Engelman the director of Population Action International (a US think tank), the United States, Canada, Europe and Japan all have national birth rates of less than 1% of the total population. Middle Eastern and Chinese countries are at 2% and the Sub-Saharan Africa at 3%.

At the same time there is an alarming trend in the decline in the rate of male births. Traditionally in the past the sex ratio for birth rates was 100 girls per 105 boys. This is widely believed to be a natural balance, as death rates among male fetuses and infants are typically higher. However, as modern medicine makes it possible for more babies to live to term, and more infants to live through childhood, it has increased the number of living boys when compared to the number of girls. For decades, more boys than girls have been born in most parts of the world, yet the male birth rate has been declining for over 30 years.

What is Causing This Trend?

A well known study documenting this change was done at the University of Pittsburgh Health Sciences headed up by Dr.Devra Lee Davis PhD, M.P.H. The research showed that in the United States since 1970 when the ratio was ‘17 less males born per 10,000 females’ the figure has multiplied to 135,000 less male births over the five-year period from 1998 to 2002. The statistics for this research were compiled from the National Center for Health.

No knows for certain why male birth rates are dropping. Some scientists argue that it is just a change in the natural fluctuations of population patterns. Others claim that economic hardship and stress play a role and now growing bodies of experts are convinced that environmental pollution such as exposure to pesticides, mercury, lead and other heavy metals, solvents, and dioxins are the largest contributing factor. There is also growing concern that certain synthetic chemicals known as endocrine-disrupters are damaging the unborn, particularly male fetuses.

Is Climate Change Contributing to the Decline in Male Births?

In association with growing concerns that environmental pollution may be the cause of declining male birth rates, there is increasing interest in whether rising global temperatures, or global warming, may also be an attributing factor. At the forefront of these speculations is substantial evidence suggesting that sperm are heat sensitive.

Scientists have found that an increase in testicular temperature of only a few degrees, such as in cryptorchid men, can cause male infertility (Steinberger 1959). Prolonged or regular exposure of the testes to higher than usual temperatures causes a decreased sperm count and decreased swimming strength of the remaining sperm. Since y-chromosome spermatozoa have been found to have a shorter life span (3 days) compared to x-chromosome spermatozoa (5 days), swimming strength of heat damaged sperm may drastically change the number of y-chromosome spermatozoa able to reach a fertile egg, resulting in fewer males conceived.

How Global Warming Contributes to This Trend

The relationship between heat and male infertility is well known and proven. Dr. Raymond Cowles a biologist at the University of California claims that the dinosaurs are extinct because of this heat sensitivity. His theory is that the dinosaurs died off during a planetary interglacial heat wave that sterilized their sperm. Because men’s scrotums (containing their testicles) are located on the outside of the body, they are especially sensitive to heat. The cooling systems in men’s scrotums insure that they are normally kept anywhere from 2°C to 15°C cooler than the rest of their bodies.

Scientists have heated the testes of animals causing temporary sterilization in dogs, rabbits, sheep, cats and bulls. Other species such as lizards and sparrows will only mate when their body temperature is lower than normal. Human couples trying to conceive are advised that the men should not take hot baths, have Jacuzzi’s or saunas. It can take up to three months for sperm to rejuvenate from heat damage. Other causes of raising the scrotum temperature are heated waterbeds, electric blankets, sitting or driving for long periods, and using a laptop computer on your lap.

How Environmental Pollution Might Also Be a Factor

Whether it is the indirect effects that environmental pollution is having on global temperature, or the direct effects environmental pollution is having on humans, the declining male birth rate trend is cause for concern. There is new speculation within the scientific community that Homo sapiens could go the way of the dinosaurs. An Environmental Health Perspectives publication states that the highest sex ratio decline in the world is at the Aamjiwnaang First Nations reservation in Canada.

Located just across the border from Michigan, this small 3000-acre area has only 46 males born to every 132 females. The reservation is surrounded on three sides by petrochemical, polymer, and chemical industrial plants, has a creek running through it heavily contaminated with mercury and PCBs, and air quality tests show the highest toxic levels in all of the country.

One thing all the scientists and experts agree upon is that much more extensive research is needed to fully study the impact of environmental pollution and contamination is having on human beings, our birth rates, and the survival of the males of our species.