For the first time, a large, uniform sample collected in south India for a study has revealed that the presence of the genetic mutation for lighter skin - found in 'almost 100%' of Europeans - broadly conforms to many cultural and linguistic differences, as well as ancestral, in the wider Indian population.
The genetic mutation in SLC24A5 is known to be pivotal in the evolution of light skin, and is responsible for a significant part of the skin colour differences between Europeans and Africans.
The study conducted partly at the University of Cambridge suggests that natural selection is not the sole factor in skin tone variation across the Indian sub-continent, and that cultural and linguistic traits still delineate this skin pigment genetic mutation.
The genetic mutation in SLC24A5 has a common origin between Europeans and Indians, according to the researchers.
But while the complete dominance of the gene in Europeans is likely to be solely down to natural selection, they say, the rich diversity of this genetic variant in India - high in some populations while non-existent in others, even neighbouring ones - has some correlation with factors of language, ancestral migration and distinct social practices such as limiting marriage partners to those with specific criteria.
The researchers say the findings display an "intriguing interplay" between natural selection and the "unique history and structure" of populations inhabiting the Indian subcontinent.
"In India, this genetic variant doesn't just follow a 'classical' theory of natural selection - that it's lower in the south where darker skin protects against fiercer sunlight," said study co-author Mircea Iliescu.
"The distribution of the SLC24A5 genetic variant in India follows patterns very much influenced by population. Understanding the genetic architecture behind the remarkable skin colour variation found today in the populations of India has the potential to shed light on the wider mechanisms responsible for creating diversity throughout human evolution," Iliescu said.
"This study helps us understand various other mechanisms that could have contributed or shaped the existing biological spectrum of human skin colour besides natural selection," she added.