Anthropology, University of South Florida
April 17, 2020 , Platinum Ballroom
The evolutionary forces that lead to the distribution of the C677T mutation in the MTHFR gene is debated. We ask why this allele, notorious for its deleterious effects, is highly frequent in several human populations.
We look at the correlation between insolation, T-allele-frequency and skin-color-measures taken in the same population. We present skin-color-measures obtained with the three filters most frequently used in the EEL apparatus: F425 mμ, F545 mμ, and F685 mμ. Most of the populations which were surveyed were from Eurasia.
Our sample size includes at least 30 data points for which we have data for all the variables. The correlation between the T allele and insolation is negative and highly significant (rs=-0.57,n=36,p= 0.0002), confirming that the T allele has low frequencies in populations exposed to high solar radiation. The correlation between the T-allele-frequency and the measures taken by the three filters at the same populations were significantly negative. Thus, the allele is not found in darkly-pigmented populations. The correlation was particularly strong and linear for the F685 filter (rs=0.73,n=35,p=0.0001). The MTHFR gene is involved in the folate cycle and is thus affected by UV radiation. Here we have shown that the distribution of the allele is correlated with skin color and insolation. However, the eventual phenotype of this mutation (hyperhomocystenia) may have been naturally-selected for an entirely different reason, despite its many poor health effects. Indeed, the world-wide distribution of this allele does not form a smooth cline (such as the skin-color cline), suggesting localized adaptation.