When people ask what I do, I always prepare myself for the often-quizzical look I get when I respond, “I look at the difference between using a tool with a handle and a tool without a handle”. Now, this is of course a simple explanation of my PhD project. Nonetheless, at its most basic level, it is what I am studying. More specifically, I am investigating the origins and influence of hafted tools (or composite technology) on human evolution.
Whilst hafting (the attachment of a shaft or handle to a tool (Figure 1)) may seem a relatively simple thing by modern technological standards, its importance to understanding human cognitive, behavioural and biological evolution should not be underestimated. The origin of hafting in the archaeological record (500 thousand years ago) has been intimately linked with human cognitive and social evolution. Others have speculated on the anatomical and physiological benefits on its users, suggesting hafted tools are more effective and more efficient than the equivalent hand-held tool at completing a given task (e.g., chopping, scraping and cutting).
Figure 1: Hafting (The attachment of a shaft or handle to a tool)
Although it may seem obvious and logical that a tool with a handle is better than one without, my questions include: If hafted tools are more efficient and effective, how do these mechanical advantages manifest themselves in the way that we (humans and our hominin ancestors) use tools? Do we change the way our bodies move when we use them? Do we use different muscles? Do we use more/less energy?
To investigate this, I have invited physically fit individuals (male and female) to take part in a carefully constructed laboratory experiment designed to investigate just these questions. Participants are fitted with markers and sensors that collect three different pieces of data: kinematics, electromyography (EMG) and respirometry (VO2) (Figure 2) and asked to complete two tasks (chopping and scraping) that each include two conditions (hafted and hand-held). For the chopping task, participants are asked to chop a wooden hardwood dowel for a total of five minutes, aiming to remove as much wood as possible (Figure 3). For the scraping task, participants are asked to scrape pieces of carpet for five minutes, aiming to remove as much fibre as possible (Figure 3).
Figure 2: Anterior, lateral and posterior of a participant with kinematics markers, EMG sensors and respirometry mask fitted
During each task, data is collected from the three data collection equipment ready for analysis. Kinematics and EMG data is collected at regular intervals during the middle three minutes of the five minute test. The video below shows how the reality of chopping transfers to raw kinematic data. Later, this data will be analysed to investigate any changes in motion, joint angles and muscle use of the upper limb between the hafted and hand-held conditions. Each wooden dowel and piece of carpet is weighed before and after each test to calculate the performance of the participant and tool in each task. This ‘measure of performance’ will then be combined with the VO2 data collected during each task to assess the energetic efficiency of each tool.
Data collection is almost complete and following this, analysis of the data will go into full flow so check back soon to see what the data tells us about the influences of the transition from hand-held to hafted tools and most importantly if we have managed to get a handle on handles.
By Dominic Coe