This is a good question to ask, since crafting an projectile point from stone consumes more time, effort and resources than simply sharpening the end of the shaft that you'll be making anyway. Hell, one could even argue that knapping a stone point incurs some additional risk since you risk slicing up your hand as you do so, as anyone who's ever tried their hand (eh!) at flintknapping knows all too well. These costs are all the more important to keep in mind given the frequency at which stone points break during use (Waguespack et al. 2009:787).As the authors argue, it's generally assumed that stone makes for a more effective projectile point, though this has rarely, if ever, been tested empirically. As they state:
"Numerous ‘common knowledge’ explanations appear to be generally accepted regarding the superiority of stone, and to a lesser extent, osseous point tips relative to sharpened staves (e.g. Guthrie 1983; Arndt & Newcomer 1986). Assumptions concerning performance (e.g. durability of the tip), lethality (e.g. length of cutting edge, depth of penetration) and aerodynamics (e.g. weight distribution, flight paths) abound. Unfortunately, few of these assumptions have been verified experimentally (Waguespack et al. 2009:787)."
To test whether stone is actually more efficient, Waguespack et al. (2009) (available as a free pdf here)made replicas of six wooden and six stone-tipped arrows and shot them at a human torso-shaped block of ballistic gel, draping it with caribou hide in some cases to simulate the arrow having to pierce the thick skin of some animals. They conducted two tests. The first, designed to see whether stone and wood tips penetrate a target more or less deeply, had the arrows shot from a compound bow 1.1m away from the target. The second, designed to see if the two types of arrowheads have different degrees of accuracy, had the arrows shot from the same contraption but at a distance of ca. 16.75m.
Picture of the experimental set-up used by Waguespack et al. 2009.
(from Waguespack et al. 2009: Figure3, p. 794.)
The results of these experiments indicate that both arrow types bestow equal degrees of precision to their users and, most importantly, that stone-tipped arrows provide only marginally higher degrees of target penetration (about 10% more), especially considering that both arrow types penetrated more than 20cm into the target. These observations lead the authors to conclude that the benefits of using stone-tipped arrows probably do not make up for the extra time, resources and risk involved in making them. Therefore, they argue, it is likely that the ubiquity of stone tips is driven by some other consideration, either other parameter of hunting effectiveness or social dimensions of projectile point making, such as the prestige derived from skillful stone working.
While there is some ethnographic evidence for the functional argument (e.g., Ellis 1997), Waguespack et al. (2009) provide a good discussion of why stone points are effective conveyors of social identities and/or a form of costly signaling. Costly signaling basically refers to behaviors that are not strictly functional but nonetheless serve to augment the social standing of the people able to effectively engage in them, be it through more finely honed skills or access to resources unavailable to others (or their profligate use).
Currently having lithics on the brain since I'm preparing to teach my Lithic Analysis seminar this coming terms (there's still some open seats if you're an interested student living in Colorado!), I thought this was a really good study that yields both interesting results and a powerful demonstration of how experimental archaeology can help answer long-standing anthropological questions (and, in this case, in a manner appealing to a wide audience!). With that in mind, I was nonetheless left wondering whether results might have differed if other types of projectiles had been used (e.g., darts propelled using a spear thrower, or hand-cast spears or javelins). Likewise, I would have been really interested in seeing the penetration results of both point types in the accuracy experiment, since 16.75m (ca. 50 feet) is likely to have been a more appropriate prey-hunter distance approximation than 1.1m (ca. 4 feet) used in the penetration experiment.
In any case, if the authors are right, this opens up some really interesting avenues to research technologically-mediated costly signaling in the deep past. Since stone points were used as far back as the Middle Paleolithic and Middle Stone Age (ca. 300,000 years BP), it implies this practice may be quite old. In sum, this paper provides a good theoretical and empirical basis to ground studies of costly signaling as reflected in some classes of chipped stone implements (i.e., points) which are certainly better in that respect than handaxes, as I've discussed recently.
Update: Turns out this episode already aired a long time ago, on Feb. 13, 2008 to be precise. That's what I get for not having cable, let alone a TV!
References
Ellis, C.J. 1997. Factors influencing the use of stone projectile tips: an ethnographic perspective, in Projectile technology (H. Knecht, ed.), pp. 37-74. New York, Plenum Press.
Waguespack, N.M., Surovell, T.A., Denoyer, A., Dallow, A., Savage, A., Hyneman, J., & Tapster, D. (2009). Making a point: wood- versus stone-tipped projectiles Antiquity, 83: 786-800
