As carnival gets into full swing, a foreign traveller enjoying the party atmosphere might be confused about the ethnicity of their fellow revellers. Latin America is a melting pot of people from all races and with all skin tones.

Recent work by researchers at the  University College London (UCL) Genetics Institute published in the journal Nature Communications has used the genomes of over 6000 Latin Americans to understand the evolution of fair skin in European and Asian populations.

Frevo_dancers_-_Olinda,_Pernambuco,_Brazil(4)

Image: Prefeitura de Olinda [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)%5D

Pigmentation genes dictate skin, hair and eye colour. Variations in the genetic code (genetic polymorphisms) of these genes are attributable to the variations in human skin colour. Exploring patterns in these variations can contribute to our understanding of significant evolutionary events such as the lightening of human skin tone.

To-date, most of these variations have been identified in European-derived populations however, in order to gain a fuller picture of how and why humans have developed different skin tones, studies must be done in non-European populations. The recent study by Adhikari and colleagues has investigated the variations of skin pigmentation genes in a Latin American population.

In accordance with Darwin’s theories, it is thought that human pigmentation has been influenced by factors such as UV radiation. One theory is that lighter skin tones, associated with Europeans and East Asians, are found further away from the equator, in reaction to reduced sunlight. Work by the researchers supports this theory and suggests that these two groups may have evolved lighter skin independently.

Latin Americans genetic heritage are a mixture of Native American, European and African. As Native Americans are ancestors of Eastern Asians it was expected that Latin Americans would share the same genetic variations in their pigmentation genes as East Asians.

By analysing the genomes of over 6000 Latin Americans and by looking at the light reflection from the participants skin, the researchers identified multiple new genetic variations associated with skin tone. One important variation was found in the gene MFSD12, called Y182H, which is associated with lighter skin and was common to East Asians and Native Americans but not Europeans. MFSD12 has been previous linked to impacts on pigmentation in Africans.

The researchers identified that in the East Asian population, the increased frequency of the Y182H variant was correlated with the intensity of solar radiation. So the East Asian population probably developed lighter skin due to the reduction in sunlight at higher latitudes. Lighter skin tone appears to have evolved independently in Europe and Asia, probably caused by the movement of these two groups into geographical areas with reduced solar radiation intensity.

Light skin is often considered synonymous with Europeans and the migration of humans out of Africa. However, this study highlights the importance of looking beyond European populations for clues into genomic and evolutionary heritage.

Reference: Adhikari et al. 2019. A GWAS in Latin Americans highlights the convergent evolution of lighter skin pigmentation in Eurasia. Nature Communications. http://dx.doi.org/10.1038/s41467-018-08147-0.