Using a very large lexical database and generalized additive modeling, this article reveals that labial-velar (LV) stops are marginal phonemes in many of the languages of Northern Sub-Saharan Africa that have them, and that the languages in which they are not marginal are grouped into three compact zones of high lexical LV frequency. The resulting picture allows us to formulate precise hypotheses about the spread of the Niger-Congo and Central Sudanic languages and about the origins of the linguistic area known as the Sudanic zone or Macro-Sudan belt. It shows that LV stops are a substrate feature that should not be reconstructed into the early stages of the languages that currently have them. We illustrate the implications of our findings for linguistic prehistory with a short discussion of the Bantu expansion. Our data also indirectly confirm the hypothesis that LV stops are more recurrent in expressive parts of the vocabulary, and we argue that this has a common explanation with the well-known fact that they tend to be restricted to stem-initial position in what we call C-emphasis prosody.