Stone flaking is achieved through integral sets of geometrical identifications and motor actions collectively referred to as the 'flake unit'. Early trends in technological evolution involved elaborating the internal complexity of the flake unit and later trends involved elaborating the way that flake units were combined. Studies by developmental psychologists suggest that internal and external increases in complexity reflect advances in cognitive ability. Homo floresiensis combined the simplest type of flake units by arranging them in chains rather than stacking them hierarchically. Thus Homo floresiensis lithic technology does not indicate high levels of cognitive ability.

Human infants and primates use similar strategies to organize utterances and motor actions. These strategies, called "grammars of action," are initially similar followed by an ontogenetic divergence in children that leads to a separation of complex linguistic and action grammars. Thus, more complex grammars arose after the emergence of the hominin lineage. Stone tools are by-products of action grammars that track the evolutionary history of hominin cognition, and this study develops a model of the essential motor actions of stoneworking interpretable in action grammar terms. The model shows that controlled flaking is achieved through integral sets of geometrical identifications and motor actions collectively referred to as the "flake unit." The internal structure of the flake unit was elaborated early in technological evolution and later trends involved combining flake units in more complex ways. Application of the model to the archaeological record suggests that the most complex action grammars arose after 270 kya, although significant epistemological issues in stone artifact studies prevent a more nuanced interpretation.

The emergence of stone-tipped projectile weaponry was an important event in hominin evolution. A common archaeological approach to identifying projectile weapons is to extrapolate from optimal values of ballistically-relevant attributes as determined from ethnographic North American weapons and modern experiments. Among the most significant of these attributes is "tip cross-sectional area" (TCSA) because it determines a point's efficiency in penetrating an animal. The warranting argument for projecting these data onto prehistoric artefact's is that past "research and development" necessarily led to stone projectiles with optimal TCSA values for a given delivery system. However, our test of this warranting argument, involving analysis of 132 hafted ethnographic Australian stone projectile points and 102 hafted knives, demonstrates that Aborigines did not optimize TCSA values, thus offering a challenge to TCSA-based narratives about the first appearance of projectile weaponry. This illustrates the difficulty of inferring ancient stone workers' design intentions from narrowly-defined optimal values. Instead, tool designs should be considered in the context of the reduction sequences that produced them and the dynamics of transmission of those reduction sequences across generations.

The 'Movius Line' is the putative technological demarcation line mapping the easternmost geographical distribution of Acheulean bifacial tools. It is traditionally argued by proponents of the Movius Line that 'true' Acheulean bi faces, especially hand axes, are only found in abundance in Africa and western Eurasia, whereas in eastern Asia, in front of the 'line', these implements are rare or absent altogether. Here we argue, however, that the Movius Line relies on classifying undated surface bi faces as Acheulean on typological grounds alone, a long-standing and widely accepted practice in Africa and western Eurasia, but one that is not seen as legitimate in eastern Asian contexts. A review of the literature shows that bifaces are relatively common as surface finds in Southeast Asia and on this basis we argue that the Movius Line is in need of reassessment.

Stone tools emerged at least 2.5 mya in Africa and were manufactured continuously by early 'Homo' species through the emergence of cognitively modern 'Homo sapiens'. Aspects of hominin cognitive evolution, reflected in hominin intentions, may therefore be preserved in this durable aspect of the archaeological record. Stoneworking design space is cellular in structure and two levels of hominin intentions are apparent in modifying stone: the intention to remove a single flake and the higher-order intentions reflected in the ways that flakes are combined to produce effects. Archaeologists have traditionally interpreted early hominin intentions using the higher-order skills and experiences of modern knappers as analogues, an approach that is epistemologically flawed. Further, the tightly constrained structure of design space could have led early hominins inadvertently to produce what appear to be highly-designed tools or tool attributes in the absence of an intention to do so. Controlled experimental research is necessary to provide an empirical baseline for identifying higher-order intentions in the archaeological record.