About 20,000 years ago, a person lived somewhere in the Middle East or Central Asia who bequeathed the genetic coding variant for lighter skin not only to all Europeans, but also many Indian people.
“We don’t know if this human dwelt in Mesopotamia, Iran, or the valley of Fergana, but clearly that’s where the light skin color has its beginnings,” said Richard Villems, a professor of archaeogenetics at the University of Tartu.
An international team of scientists, co-led by researchers from the University of Tartu, Estonian Biocentre and University of Cambridge, studied one of the most important skin pigmentation genes — SLC24A5. A variation in this gene has been known to explain why Africans have dark skin, while Europeans, on the other side, are light-skinned. The present study showed that this particular genetic variant, known as rs1426654-A, has given light skin color not only to Europeans, but is also omnipresent in the Indian subcontinent.
In Africa, the original home to humankind, dark skin is necessary for survival, as it offers protection against the harmful ultraviolet (UV) radiation of the sun. However, as humans started to move towards the north, characterised by low UV levels, light skin offered a selective advantage — when exposed to sunlight, the light-skinned body can produce more vitamin D.
According to Villems, the mutation causing lighter skin colour occurred to the aforementioned ancestor of Europeans and Indian people about 20,000 years ago, and for some reason, natural selection started to favour it.
Although the genetic basis of skin pigmentation amongst Europeans has been researched to a large extent, South Asia — home to about a fifth of the world’s population, with a large variety of skin tones — has somehow escaped observation until now.
The present study provided the first detailed map of the genetic variant using more than 1,600 individuals representing 54 South Asian ethnic groups. Although one might presume that skin colour in India becomes lighter from south to north, this was not the case. Rather, the pattern of the light-skinned genetic variant could be tracked down to different geographical, socio-cultural, and linguistic barriers, thus offering a hint that in addition to being conditioned by the ultraviolet radiation, demographic history also plays a part in skin colour.
“Although UV rays stand as the major driving force behind the geographical stratification of skin colour across the globe, this study helps us elucidate other possible evolutionary forces further contributing to the fine-tuning of skin colour diversity,” explains Chandana Basu Mallick, first author of the study, doctoral student at the University of Tartu, and researcher at Estonian Biocentre.
According to Villems, it is interesting that people living in South-East Asia, i.e. Malaysia, Vietnam, and Laos, do not have the same gene variation as the reason for their lighter skin. Thus, the hereditary factor favouring lighter pigmentation has been chosen by natural selection on at least two separate occasions during human history.
SLC24A5 is also known as ‘the golden gene’, because this mutation was first discovered in zebrafish. The species’ golden stripes are caused by this gene.
Basu Mallick C, Iliescu FM, Möls M, Hill S, Tamang R, et al. (2013). The Light Skin Allele of SLC24A5 in South Asians and Europeans Shares Identity by Descent. PLOS Genetics DOI: 10.1371/journal.pgen.1003912.