One of the strongest patterns in obsidian distributions in the south-central Andes is the sudden onset of obsidian use with series 5 projectile points in the Terminal Archaic, after 3300 cal BCE In defining the small type 5D projectile points Klink and Aldenderfer(2005: 54)suggest that the widespread adoption of these point types may reflect the use of bow and arrow technology, as these points fallwithin the size range described by Shott (1997: Table 2) as associated with arrow points (although with substantial overlap with the size of the smaller dart points).

Figure 3-14. Type 5d projectile points from a Terminal Archaic level at Asana and Early Formative levels at Qillqatani, from illustration in Klink and Aldenderfer (2005: 49).

Additional metrics for differentiating arrowheads from dart and spear points have been suggested by Thomas (1978: 470) and Patterson (1985). With Mesoamerican projectile points, Aoyama (2005: 297) has found a very significant correlation between evidence from microwear analysis and projectile dimensions in his effort to differentiate arrowheads from dart and spear points. The relationship between the mass of the item and the velocity and distance of the projectile are discussed in detail by Hughes (1998). She notes that the innovation of fletching allowed for balanced projectiles that had smaller projectile tips and lighter shaft materials, which in turn permitted greater distance and velocity in weapons systems (Hughes 1998). On a related point, the notched base in all type 5 projectile styles reflects a change in hafting technology. Greater impact loads can be absorbed by mounting projectiles tips with notched bases into slotted hafts (Hughes 1998: 367;Van Buren 1974).

Obsidian has a number of attributes that make it a particularly effective material for projectile point tips, most notably are the predictableconchoidal fracture qualities of obsidian that allow it to be pressure flaked into very small projectile points. The sharpness of freshly knapped obsidian margins is unrivalled, andethnographicallyobsidian is renowned as a brittle material that can fracture on impact, causing the fragments to produce greater bleeding in the victim of an obsidian projectile (Ellis 1997: 47-53). In materials science, obsidian has extremely low compression strength because it has no crystalline structure (Hughes 1998: 372). Due to the brittleness or lack of compression strength, missed shots can result in many broken obsidian projectile tips, and perhaps for this reason obsidian was not the predominant material for projectile point production until after the domestication of camelids when hunting was decreasingly the primary source of meat (as inferred from the ratio of camelid to deer bone in excavated assemblages).

Increased velocity and distance is possible with the use of bow and arrow, and obsidian has greater penetrating power, although lower durability, than other material types. Do these changes suggest a greater use of projectiles for warfare? Greater use of small, fletched projectiles might be expected in contexts where the individual needs (1) increased distance from the target (2) increased velocity, perhaps due to change in prey or to the use of padded armor. The use of obsidian may increase in contexts where one needs (1) a material that can be knapped into small, light projectiles as discussed above, (2) increased penetration with sharper material, (3) decreased concern for durability because in warfare the weapon will perhaps be retrieved by the opponent.

Although empirical evidence for warfare is scarce in the Terminal Archaic in the highlands, a study of 144 Chinchorro individuals from Terminal Archaic contexts in extreme northern Chile found that one third of the adults suffered from anterior cranial fractures that probably resulted from interpersonal violence, and men were three times more likely than women to have these wounds (Standen and Arriaza 2000). These wounds appear to have been caused by percussion weapons like slings, but the coastal evidence for interpersonal violence in this time period is strong. Additional support for the introduction of the bow and arrow in the Terminal Archaic come from the region among Chinchorro burials in coastal Northern Chile. Bows among the Chinchorro grave goods date to circa 3700 - 1100 cal. BCE, or the Terminal Archaic and Early Formative (Bittmann and Munizaga 1979;Rivera 1991;Standen 2003).