Saturday, April 12, 2008

Plio-Pleistocene butchery I just read a paper in the Journal of Archaeological Science by Braun, Pobiner, and Thompson titled An experimental investigation of cut mark production and stone tool attrition (see full ref below). My first thought was "Gee, another cut experimental mark paper? Didn't they do all of that 30 years ago?". Well, yes and no. A lot of work was done in the 1970s and '80s on identifying cut marks on bone that were a result of hominid activity and differentiating them natural sources. I even participated in a little experiment with Bunn when a young undergrad. We were asked to do various tasks on a carcass with stone tool flakes to see what sort of cut marks were produced. First we removed a leg quickly, as if we had stumbled upon a carnivore kill and wanted to grab a hunk of meat before said carnivore returned (all the while Bunn shouting stuff like "Hurry! The hyenas are at the top of the hill over there!"). Then we were able to take our time -- as if we had killed the critter -- and remove a leg carefully, getting all that we could. The idea was to differentiate scavenging from hunting just from the character of the cut marks.

This study is not looking at cut marks per se but at edge damage resulting from butchery. My second thought was "Nobody has done this before? I did that as a lab project in my second year of grad school." Really, I took a few flakes and measured edge damage after I had used them in different ways on different materials. Pretty interesting, I should try to find that and post the results.

Anyhoo, here is the abstract:
In discussions of Paleolithic hominin behavior it is often assumed that cut marks are an unwanted byproduct of butchery activities, and that their production causes the dulling of stone tool edges. It is also presumed that Paleolithic butchers would have refrained from making cut marks to extend the use life of their tools. We conducted a series of butchery experiments designed to test the hypothesis that cut marks affect the use life of tools. Results suggest cut marks are not associated with edge attrition of simple flake tools, and therefore it is unlikely that Paleolithic butchers would have avoided contact between bone surfaces and tool edges. Edge attrition is, however, significantly greater during skinning and disarticulation than during defleshing. This suggests that skinning and disarticulation activities would require more tool edges relative to butchery events focused purely on defleshing. Differences between the number of cut-marked bones relative to the number of stone artifacts deposited at taphonomically comparable archaeological localities may be explicable in terms of different types of butchery activities conducted there, rather than strictly the timing of carcass access by hominins. Archaeological localities with higher artifact discard rates relative to raw material availability may represent an emphasis on activities associated with higher edge attrition (e.g. skinning or disarticulation).

They are differentiating three activities: Skinning (self explanatory), disarticulation (removing limb bones from the axial skeleton and removing bones from one another), and deflishing (removing the meat from the bone). What they showed is that edge attrition -- wearing down of the cutting edge -- was not statistically associated with the number of cut marks observed on the bones. That is, cut marks are not predictive of edge damage and eventual discarding of the tools:

Given that two of the three measures of edge attrition show
highly significant differences between certain butchery activities,
we conclude that there are much higher attrition rates in
flakes used for skinning and disarticulation than those used for
defleshing only.

Their conclusion:
The results of our experiments provide no statistical support
for Bunn’s (2001) inference that hominins took measures
to reduce the likelihood of tool-bone contact because of potential
edge dulling caused by cut mark production. Our results also lead to the expectation that tool discard behavior should
not necessarily be associated with high frequencies of cutmarked
bone, and this expectation can be tested at a variety
of archaeological localities. A brief investigation of stone artifact
discard patterns at Early Stone Age sites suggest that
hominins are discarding artifacts at very high rates even at
sites when there is very little evidence of butchery activity
(Table 4). However, we still expect that stone tool discard rates
may be associated with the degree of edge attrition. Given the
differences in tool edge attrition described in this study, the
frequency of different types of tasks may have had a substantial
effect on rates of tool discard at different archaeological localities.
This raises the possibility that stone tool discard was
linked to butchery activities that did not always result in
high numbers of cut marks.

Thus, cut marks are not indicative in and of themselves of greater use wear and wastage of stone tools (and hence greater discard rates). They mention other possible sources of discard rate variation, prominently featuring raw material quality and availability. These have been shown to affect the degree to which stone tools were curated and discarded: rare and distant materials were more heavily conserved whereas abundant materials were used somewhat wastefully (I have some discussion and references of that here).

BTW, they used way more techy measures than I did in my little study. I weighed the flakes as they did but instead of calculating area with a fancy digital imaging technique, I drew a line parallel to the edge and measured the distance to the edge in several places. That way I could who the rate at which the edge was being ground down. I don't recall if I measured edge angle. . .but I did note the kind of wear that was being inflicted on it (flaking vs polishing vs crushing).

Ref: David R. Braun, Briana L. Pobiner, Jessica C. Thompson 2008 An experimental investigation of cut mark production and stone tool attrition. Journal of Archaeological Science 35:1216-1223.