When was silcrete heat treatment invented in South Africa?

Silcrete heat treatment, along with a suit of other innovations, have been used to argue for an early onset of modern or complex behaviours in Middle Stone Age hominins. This practice was confined to South Africa's southern and western Cape regions where it was continuously practised since the Still Bay industry. However, the exact moment that this technological advancement occurred still remains unclear. This is partly due to the scarcity of silcrete assemblages dating to the first half of the Middle Stone Age. To determine when silcrete heat treatment began to be well-established, we compare the silcrete assemblages from two archaeological sites situated along the south western coast of South Africa: Hoedjiespunt 1, one of the earliest Middle Stone Age silcrete assemblages dating to 119-130 ka, and Duinefontein 2, one of the latest Early Stone Age assemblages dating to 200-400 ka. Our results suggest that the invention of heat treatment occurred sometime between 130 ka and 200-400 ka, as it is still absent in the earlier assemblage but fully mastered and well-integrated in the recent one. This period corresponds to the time that Homo sapiens became the major hominin species in the southern African subcontinent and it is roughly the time that silcrete use became widespread in the second half of the Cape-coastal Middle Stone Age. This opens interesting new questions on the relation between silcrete use and heat treatment and on why early modern humans spontaneously invented heat treatment when they began using silcrete in the Cape region.