The influences of genes, the environment, and social factors on the evolution of skin color diversity in India

Abstract

India is a crucible of macro- and micro-evolutionary forces, and the complex interactions of physical and social forces are visible in the patterns of skin color seen today in the country.

The evolution of human skin pigmentation involved the interactions of genetic, environmental, and cultural variables

“…One of the most distinctive aspects of population structure in the subcontinent is the pattern of endogamy within groups, including within the hierarchically arranged Hindu castes (Majumder & Basu, 2014 ). Because of the complex pattern of dispersal and the prevalence of within‐group marriage, the subcontinent is more accurately described as a genetic mosaic and, not surprisingly, social factors and population structure have played a stronger role than natural selection in shaping skin color diversity across the region (Iliescu et al., 2018 ; Stokowski et al., 2007 ). Two striking findings have emerged from studies of skin pigmentation diversity in the subcontinent to date.…”

“…Two striking findings have emerged from studies of skin pigmentation diversity in the subcontinent to date. The first is that while the range of skin pigmentation phenotypes across the breadth and length of the subcontinent is vast (Jablonski & Chaplin, 2000 ), the pattern is not strongly correlated to strength of UVR (Iliescu et al., 2018 ). The second is that the classic skin lightening variant of SLC24A5 is present in high frequencies in most populations but is not expressed (Basu Mallick et al., 2013 ; Iliescu et al., 2018 ).…”

“…The first is that while the range of skin pigmentation phenotypes across the breadth and length of the subcontinent is vast (Jablonski & Chaplin, 2000 ), the pattern is not strongly correlated to strength of UVR (Iliescu et al., 2018 ). The second is that the classic skin lightening variant of SLC24A5 is present in high frequencies in most populations but is not expressed (Basu Mallick et al., 2013 ; Iliescu et al., 2018 ). Thus, epistasis has affected the expression of the SLC24A5 in such a way as to prevent the allele's ability to lower eumelanin production (Quillen et al., 2019 ).…”

“…The reasons behind this can be traced potentially to the specific and distinct genetic backgrounds, including social selection and sexual selection, that contributed to the unique reproductive structure of the Indian populations, but the relative importance of these phenomena is not clear at present. This result should be seen as a useful cautionary tale for forensic reconstruction of skin pigmentation, viz., specific genotypes are not associated reliably with specific skin color phenotypes (Iliescu et al., 2018 ; Quillen et al., 2019 ).…”

“…What seems likely is that sexual selection has probably played a secondary and complementary role in the evolution of skin pigmentation, primarily through manipulating levels of existing sexual dimorphism (Jablonski, 2012 ; Jablonski & Chaplin, 2000 ; Quillen et al., 2019 ). This apparent directional preference for women with lighter skin appears to be particularly strongly marked in Island Melanesia, Japan, and among certain populations in India where cultural preferences for lighter females are strongly culturally reinforced (Iliescu et al., 2018 ; Jablonski, 2012 ; Norton et al., 2006 ). It would be surprising if uniform, global patterns of sexual selection applied because these would rely on uniform preferences (Quillen et al., 2019 ).…”