I wander about the 1st west African to get lactose intolerance. See, most West-African aren't cattle herder. We live in the rain forests (a.k.a jungle), and cattle seems to prefer to eat grasses, which is more prevalent in the Savannah region north of our abode. Therefore we choose to be farmers and hunters. Suites our environment better. Good soil, lots of animals and plenty of rain. This is why our bowel to this day can not adapt fully to milk.
So, imagine this first West-African to get Lactose intolerance. He had travel to a cattle herding society and drank this stuff which seems to be delicious. Now he is stomach is cramping and he is passing gas like crazy.