"The spread of fresh milk drinking from the Balkans across Europe also explains why most European lactase-persistent people carry the same version of the gene; it surfed on a wave of population expansion that followed the rapid co-evolution of milk tolerance and dairy farming. In Africa, there are four known lactase persistence gene variants and probably many more yet to be discovered. Most are likely to be of African origin but the European version is also found there, especially among the Falani people. This diversity is probably the result of an 'imposition' of dairying culture on a pre-existing farming people, rather than the natural spread of dairy farmers."
