Basis for the gain and subsequent dilution of epidermal pigmentation during human evolution: The barrier and metabolic conservation hypotheses revisited

Abstract

The evolution of human skin pigmentation must address both the initial evolution of intense epidermal pigmentation in hominins, and its subsequent dilution in modern humans. While many authorities believe that epidermal pigmentation evolved to protect against either ultraviolet B (UV-B) irradiation-induced mutagenesis or folic acid photolysis, we hypothesize that pigmentation where little UV-B breaches the atmosphere (i.e., present-day UK, Scandinavia, Baltic States), pigment dilution alone could not suffice. There, other nonpigment-related mutations evolved to facilitate VD3 production; for example, in the epidermal protein, filaggrin, resulting in reduced levels of its distal metabolite, trans-urocanic acid, a potent UV-B chromophore. Thus, changes in human pigmentation reflect a complex interplay between latitude, climate, diet, lifestyle, and shifting metabolic priorities.

Facial skin mapping: from single point bio‐instrumental evaluation to continuous visualization of skin hydration, barrier function, skin surface pH, and sebum in different ethnic skin types

“…Nevertheless, ITA° values were correlated with skin hydration. This data appeared to be in conflict with the other data showing that the more pigmented the skin, the better the barrier of the skin . Nevertheless, these measurements were only on a defined location of the face.…”

“…The results of this study as well as earlier ones are discordant with the hypothesis that a lower pH of the outer epidermis leads to enhanced barrier function of darkly pigmented skin . There was no relationship of skin surface pH or pigmentation with superior basal barrier properties of the SC.…”

“…Depending on the facial location, darkly pigmented skin does not have a superior barrier function. Indeed, compared with Caucasian subjects the Black African subjects had a numerically or significantly higher TEWL which is diametrically‐opposed to the forearm and hand data from the group of Elias .…”

“…Our aim is to understand in more depth the complexity of facial skin and also the need for different products for differently pigmented skin types [1]. Although controversial data exist, it has been reported that the barrier of darkly pigmented skin has some advantages compared with that of lightly-pigmented skin [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. However, most of these studies have been conducted on volar forearms and hands but not on the face.…”

Identification of a novel locus associated with skin colour in African-admixed populations

“…Moreover, several selective factors have been implicated in the evolution of human pigmentation towards darker pigmentation in equatorial and tropical regions2, including: protection against the harmful effects of UV radiation exposure7; protection against folate photolysis28; maintenance of adequate levels vitamin D9; and contributing to the skin’s barrier function by optimizing water conservation and improving cutaneous antimicrobial defense10.…”