Hominin Stone Flaking and the Emergence of 'Top-down' Design in Human Evolution

The philosopher Daniel Dennett argues that complex structures in the natural and cultural worlds emerge from two types of design. Bottom-up design involves the rote action of a simple algorithm in an environment constrained by physical laws. Topdown design involves deliberation and planning, and is unique to modern humans. Identifying the emergence of top-down design in the hominin lineage is an important research challenge, and the archaeological record of stone technology is our best evidence for it. A current view is that artefact types and flaking methods increased in complexity from 3.3 to c. 0.3 million years ago, reflecting improving capacities at spatial cognition and working memory, culminating in top-down design perhaps as early as 1.75 million years ago. Recent experimental work, however, has shown that a simple 'remove flake' algorithm constrained by the laws of fracture mechanics-a form of bottom-up design-can produce stone tool attributes thought to be evidence of topdown design. Here, these models are reviewed and critiqued in light of the new experimental evidence. A revised working memory-based model, focusing on the recursive aspects of stone flaking, is proposed.