Lactase persistence in the Jordanian population: Potential effects of the Arabian Peninsula and Sahara's aridification.

The single nucleotide polymorphism (SNP) -13910 C > T has proved a good predictor of the incidence of lactase persistence in Europe and South Asia. Yet, this is not the case in the Near East, although this region is a passageway between the two continents. Lactase persistence is associated with cattle breeding, which originated in the Fertile Crescent of the Near East and spread later during the Middle Neolithic throughout Europe. Here we analyzed five SNPs (-13915 T > G (rs41380347), -13910 C > T (rs4988235), -13907 C > G (rs41525747), -14009 T > G (rs869051967), and -14010 G > C (rs145946881)) in three Jordanian human groups, namely the Bedouins, Jordan valley farmers, and Jordanian urban people. The SNPs -14009 T > G and -14010 G > C were not detected in the sample, -13907 C > G was virtually non-existent, -13910 C > T showed low frequencies, and -13915 T > G exhibited salient frequencies. The estimated incidence of lactase persistence was lower in the urban population (16 %), intermediate in the Jordan Valley's farmer population (30 %), and higher among the Bedouins (62 %). In explaining our findings, we postulated climatic change brought about by the aridification episode of the Arabian Peninsula and the Sahara 4200 years ago. This climatic milestone caused the collapse of the Akkadian Empire and the Old Kingdom in Egypt. Also, it could have led to a drastic decline of cattle in the region, being replaced by the domestication of camels. Loss of traditional crops and increasing dependence on camel milk might have triggered local selective pressures, mainly associated with -13915 T > G and differentiated from the ones in Europe, associated with -13910 C > T.