The effects of climate change, from increased greenhouse gases and other environmental factors, are predicted to have a massive impact on the overall health of the planet. Yet these profound changes will likely not be limited to just the geology and climate. Many scientists note the potential changes that will also impact the biology of human beings!
One interesting change could be the proportion of female and male newborn gender ratios. This could result in an increased number of male newborns in locations where temperatures are likely to rise and a decreased number of males born in places where other environmental changes, like prolonged drought or wildfires, are increased by climate change.
The Relationship Between Environmental Stress And Birth Rate
A Japanese research study found a potential relationship between large scale temperature fluctuations and a decrease in male-to-female gender ratio. The underlying concept is that male conception is increasingly vulnerable to external stress factors.
There was also a separate study that took an in-depth look at birth rates and gender ratios in regions that were significantly affected by a major environmental event, known to cause severe stress in the general population. This included things like the data from the Hyogo Prefecture following the 1995 earthquake in Kobe, Japan As well as Tohoku after the 2011 Great East Japan Earthquake. The study also factored in the 2016 earthquakes in Kumamoto Prefecture and the following nuclear disaster in the Fukushima power plant.
Within nine months of these major disasters, the proportion of male newborns recorded in these prefectures had decreased by an estimated 6 to 14-percent from the year before. These data segments support the theory that major stress factors have the ability to affect conception or the gestation process. This can potentially alter the ratio of male to female newborns in a region at a specific time.
This also adds credence to the concern that events related to climate change might also be able to affect the sex ratio. However, continuing research is still delving deeper into the various ways that stress can impact.
The Fragility Of Male Fetuses And Infants
One advancing theory is that there is an inherent vulnerability in Y-chromosome-bearing sperm. It is strongly believed that the sex ratio is equal at the time of conception. However, it’s also estimated that around half of all conceptions fail during the gestation phase. This can result in a sex ratio imbalance between male and female births.
There is another field or research being advanced by the University of California at Berkeley, that has found evidence supporting that the biology of a mother will spontaneously abort some early conceptions in utero. Taken on the large scale, factored with significant environmental stresses this could essentially filter out chromosomal preferences as well as things like genetic abnormalities.
Since the ovaries of a female fetus will carry all the eggs that she will ever use throughout her reproductive years, the possibility of a genetic defect being found in a female might be potentially greater than the possibility of a defect in a male fetus. Since the male fetus only carries his own genetic makeup.
When we look at global statistics the newborn sex ratio tends to average between 103 to 106 male newborns compared to 100 female newborns.
Statistically, throughout the world male infants are more likely to die prematurely. Though the underlying reasons for this are not completely understood. There are some scientists who believe that male infants are possibly more susceptible to diseases as well as premature death.
One theory related to the imbalance in the sex ratio may be tied to our underlying biology. In certain parts of the world where infant and child mortality rates are higher, a 50:50 sex ratio may actually be attained by the time those infants reach their reproductive age.
One study looked at a population of Finns, Danes, Swedes and Norwegians, and Swedes born in the years between 1878 and 1914. Statistics indicated that colder years there were fewer males born. However, this lower birth rate of male newborns also meant that the baby boys were stronger and ultimately less likely to die in infancy. As these boys grew into young men in their primary reproductive age, they tended to have a higher than expected number of children.
Climate Change And Stress In Utero
Currently, a large number of scientists and other specialists believe that the Earth is going through a time of significant change in the climate. Further many of these scientists also believe that the changes we are likely to see over the next two centuries could have dramatic swings.
Indeed, many climate models don’t just predict that Earth will become warmer, they also note that the pattern changes will become increasingly unpredictable. This could lead to much larger swings in temperature from year to year. Leading to higher highs, lower lows and rapid changes between the two.
These environmental extremes and the lack of stable patterns could do more than simply stress temperature. It could lead to things like major droughts, famine from subsequent crop failures, increased incidents of major natural disasters, and potential political strife.
Anyone or potentially all these factors can stress the human population, particularly expectant mothers. As the situations start to affect the birth sex ratio, there will likely also be different forms of human adaptation as part of the natural evolutionary response.
Warm Weather Might Increase Male Birth Rates
A study focusing on Northern Finland was able to quantify the effect that temperature has on birth sex ratio. It noted that for every 1.8-degree increase in temperature, there was also a correlating .06% increase in the healthy birth of male newborns. Based on this sample size a change of 5.4 degrees Fahrenheit, would then translate into a .18% increase in the ratio of male-to-female newborns.
At first, this might not seem like a major impact. However, on a larger scale, it could have a profound impact on population size. At the same time, regional changes in climate, and catastrophic events like wildfires, large scale flooding, and other natural disasters could create large pockets in the human population where the sex ratio is significantly different.
However, it is worth noting that there are some scientists who don’t feel that there is enough evidence to definitively indicated that climate change directly affects the newborn sex ratio. There is a trend in some populations and even entire countries where the sex ratio seems somehow biased toward a less male sex ratio. It is yet unclear whether or not this emerging trend is a direct response to global climate change. In some instances, large scale pollution problems may also be a factor.
When taken in a larger context, the importance of a change in the newborn sex ratio may have less of a societal impact, than it does medical. Essentially, the newborn sex ratio is a reproductive health indicator and extreme temperature fluctuations can impact birth weight.”
Homo sapiens have proven to be adaptable throughout evolutionary history. Just how climate change is going to change the characteristics of the human population is yet to be seen.
Source – CNN