Animal Bones from Caves to Cities: Reverse Utility Curves as Methodological Artifacts

Utility-based studies are attractive to zooarchaeologists because they afford the opportunity of investigating economic decisions relative to particular contexts. While a positive relationship between utility and skeletal element abundance is anticipated at residential sites, a reverse utility curve is most common. A popular mechanistic explanation argues that reverse utility curves result from density-mediated destruction of bone, suggesting that utility-based studies will rarely be successful as density-mediated destruction will overwhelm any skeletal element patterning created by differential transport. We show with archaeological and experimental/naturalistic taphonomic data that the mechanistic explanation is overstated. Fauna from Kobeh cave (a Mousterian site) and "Ain Dara (an Iron Age site) both show a reverse utility pattern when estimates of long bone abundance are based just on ends (the procedure followed at all sites that have shown a reverse utility pattern), and all bones are plotted together. When long bone abundance is estimated from the middle shaft portion, the reverse utility pattern collapses and a positive relationship arises. The ubiquity of the reverse utility curve derives in many cases from basing long bone abundance estimates on ends and scatter-plotting the abundance of long bones with non-long bones, thus restricting the analysis to the least dense most spongy bone portions. Long bone abundance estimates must include the middle shaft portion to attain accurate estimates of element abundance. Long bone abundance, when based on shaft portions, can be usefully compared to utility to investigate utility-based models of human behavior.