Linguistic and manual evolution

The manipulative complexity of Lower Paleolithic stone toolmaking

BACKGROUND

Early stone tools provide direct evidence of human cognitive and behavioral evolution that is otherwise unavailable. Proper interpretation of these data requires a robust interpretive framework linking archaeological evidence to specific behavioral and cognitive actions.

METHODOLOGY/PRINCIPAL FINDINGS

Here we employ a data glove to record manual joint angles in a modern experimental toolmaker (the 4(th) author) replicating ancient tool forms in order to characterize and compare the manipulative complexity of two major Lower Paleolithic technologies (Oldowan and Acheulean). To this end we used a principled and general measure of behavioral complexity based on the statistics of joint movements.

CONCLUSIONS/SIGNIFICANCE

This allowed us to confirm that previously observed differences in brain activation associated with Oldowan versus Acheulean technologies reflect higher-level behavior organization rather than lower-level differences in manipulative complexity. This conclusion is consistent with a scenario in which the earliest stages of human technological evolution depended on novel perceptual-motor capacities (such as the control of joint stiffness) whereas later developments increasingly relied on enhanced mechanisms for cognitive control. This further suggests possible links between toolmaking and language evolution.

Skeletal biology, functional asymmetry and the origins of "Handedness"

The past decade has witnessed the (re)emergence of a debate as to whether handedness is apomorphic within hominins. There are both qualitative and quantitative arguments, some which draw non-human primates into the handed sphere and others which exclude them. Ultimate questions concern origins of structural asymmetry of both brain and body and lateralized behaviours with implications for tool use and language. Lateralization is thus an important realm of phylogenetic study, and archaeologists and psychologists alike have sought to identify handedness within material culture. However, hand preference for tool manufacture and use among extant non-human primates, such as Cebus and Pan, suggests that the archaeological record may well be mute regarding the origins of laterality. In this paper, an argument is put forward positioning skeletal biology as a viable approach to the handedness origins issue. Behaviour is a mediator of the complementary processes of geometric modelling (change in size and shape) and histological remodelling (disuse osteopenia; microfracture repair); therefore, directional asymmetry in the pattern of skeletal modelling and remodelling is a putative signal of lateralized activity.