No fossils of Homo neanderthalensis have been found in Africa, but many African populations have traces of Neanderthal DNA. If Neanderthals were never in Africa (which is a possibility, though fossils may yet be found), how can the presence of Neanderthal DNA be explained?

that would be called plucking : )

explanation:

''plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the erosion and transportation of individual pieces of bedrock, especially large "joint blocks". as a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints (cracks) in the bedrock."