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Current Direction of Climate Change Could Make Humanity 25%-50% Darker!

Recent scientific study shows climate may have more to do with your complexion than partner selection!

Human skin pigmentation is the product of two clines (genetic characteristics) produced by natural selection to adjust levels of skin darkness ie pigmentation to levels necessary to protect body from UV radiation (UVR). One cline was generated by high UVR near the equator and led to the evolution of dark, photoprotective, eumelanin-rich pigmentation. The other was produced by the requirement for UVB photons to sustain cutaneous photosynthesis of vitamin D3 in low-UVB environments, and resulted in the evolution of depigmented skin. If climate change is causing a rise in temperature and UVR it will have a predictable effect on the prevalence of clines protective of high UV radiation.

The evolution of skin color in different populations is a result of adaptation to local environmental conditions, particularly the level of ultraviolet (UV) radiation. In hot, sunny climates with high UV radiation, such as in Africa, Southeast Asia, South America, The Middle East and Australia darker skin provides natural protection against the harmful effects of UV radiation, including skin cancer and folate depletion. Melanin, the pigment that gives skin its color, helps to absorb and scatter UV radiation, providing a natural defense.

Conversely, in colder climates with lower UV radiation, such as in Europe, lighter skin allows for greater absorption of UV radiation, which is necessary for the production of vitamin D. In these regions, where sunlight is less intense, lighter skin allows for more efficient production of vitamin D, which is essential for bone health. While it may seem counterintuitive that people in hot climates have darker skin, and vice versa, these adaptations have provided evolutionary advantages for different populations in their respective environments. It's important to note that in the past these adaptations occurred over thousands of years but as recent research has shown animal populations can evolve in a period of decades if the climate threatens the existence of a species. Changes can occur in mammals that are threatened with extinction as a result of natural selection and genetic variation within populations.

Roadside-nesting cliff swallows have evolved shorter, more maneuverable wings, which helped them to make hasty retreats from oncoming vehicles, this evolution has occurred in less than 100 years according to a study published in Current Biology. Typically, you would expect population genetics to take hundreds of thousands or millions of years. And while cliff swallows didn't turn into different species, they have evolved through natural selection in a surprisingly short time – just 30 years. “In evolutionary terms, 30 years is an instant in time,”

As hominins dispersed outside of the tropics, they experienced different intensities and seasonal mixtures of UVA and UVB. Extreme UVA throughout the year and two equinoctial peaks of UVB prevail within the tropics. Under these conditions, the primary selective pressure was to protect folate by maintaining dark pigmentation. Photolysis of folate and its main serum form of 5-methylhydrofolate is caused by UVR and by reactive oxygen species generated by UVA.

Solar radiation affects fertility for races differently! For younger women of any race, aged 20-29, no significant statistical relationship was found between UV exposure and AMH levels for fertility.

In general, a high level of AMH means you have more eggs available, and a low level means your egg supply is shrinking and your time to get pregnant may be shorter. On the other hand, among Black women aged 30 to 40, a statistically significant seasonal pattern emerged: these women, whose egg reserves were in decline, responded positively to sun exposure. It was affirmed in an African population that "sun exposure increased metabolism, sexual appetite and behavior, and, enlarges the ovaries.”(Tel Aviv University Feb 19th 2024)

Using data from 32 European countries for nearly 244 million live births between 1969 and 2021, A recent paper examined the effects of temperatures on birth rates. this portends a lot for a warming climate creating shorter winters and longer summers and heat waves! The results show that exposure to hot days reduces European birth rates five to eight months later, the more hot days the more pronounced the effect while much stronger negative effects are observed nine to ten months after exposure to hot temperatures.

This study also shows that the effect of high-humidity hot days is much stronger than that of hot days with low humidity. Besides, the effect of heatwave days has been found to be more severe than that of hot days that are not preceded by other hot days. This study founds that genetic adaptation to heat might be expected in the long run.

There is growing evidence that all human fertility and fetal development are considerably affected by heat exposure (Hajdu & Hajdu, 2022a). Several studies demonstrated that post-conception exposure to hot temperatures increases the chance of pregnancy losses (especially among Europeans and Pheomelanin dominant populations like Chinese and Korean and leads to shorter gestation and lowers the health of newborns! (Basu et al., 2016; Bonell et al., 2023; Davenport et al., 2020; Hajdu & Hajdu, 2021a, 2023; McElroy et al., 2022; Sexton et al., 2021),

(Andalón et al., 2016; Barreca & Schaller, 2020; Chen et al., 2020; Deschênes et al., 2009; Grace et al., 2015; Hajdu & Hajdu, 2021b; Sun et al., 2019).

Competition for folate between the needs for cell division, DNA repair, and melanogenesis is severe under stressful, high-UVR conditions and can be exacerbated by dietary insufficiency such as occurred in Europe during the Ice age. Outside of tropical latitudes, UVB levels are generally low and peak only once during the year. The populations exhibiting maximally depigmented skin are those inhabiting environments with the lowest annual and summer peak levels of UVB (the Global North). Development of facultative pigmentation (tanning) was important to populations settling between roughly 23° and 46°, where levels of UVB varied strongly according to season. Depigmented and tannable skin evolved numerous times in human evolution via independent genetic pathways under positive selection.Genes do not function in isolation but rather suites of genes act in concert to perform biological functions. When different genes function in different sequential steps of a biological process, this is known as a genetic pathway.

An example would be the hairless condition of humans which itself did not evolve because of a partiality for smooth skin, as averred by Darwin, but primarily because of the need to lose body heat from the skin's surface during exertion and under hot environmental conditions . Cooling by evaporation of eccrine sweat is impeded by thick body hair; the primary selective pressure promoting the evolution of hair loss in humans was thermoregulation. The loss of body hair in humans was accompanied by enhanced barrier functions of the outermost layer of the skin, the evolution of epidermal keratins which reduced the skin's permeability and improved its abilities to resist abrasion and microbial attack. The rapid divergence of genes responsible for epidermal differentiation was one of the most significant results to emerge in humans.

Changes in skin pigmentation for Homo Sapien populations in the north also accompanied an increased growth of body hair, and multiple lines of evidence indicate that permanent, dark, eumelanin-based pigmentation that had evolved soon after the emergence of the genus Homo in Africa were lost with the advent of populations trapped by the ice age in glaciated areas. Sexual selection was not the primary, or even a major, determinant of skin pigmentation in that case,it was natural selection it is the recent preference by males in some cultures for females of lighter color probably has heightened sexual dimorphism in skin pigmentation in some populations even though it will have a negative outcome if climate global warming continues. Essentially it was natural selection that produced the conspicuous gradient of skin tones groups primarily eumelanin dominant observed in our species as a whole.



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