Microlithic industries with ceramics became common by the Mid-Holocene, coupled with an apparent intensification of wild food exploitation. Between ~4–3.5ka, these societies gradually transformed into food producers, possibly through contact with northern pastoralists and agriculturalists, as the environment became more arid.  However, hunter-gatherers have survived in the more forested parts of West Africa until much later, attesting to the strength of ecological boundaries in this region.