Convergence as a biological phenomenon is based on the fact, that organisms originating from different lineages may develop analogous structures or organs as a response to similar environmental constraints (McGhee 2018). In living organisms analogous organs or structures occur by means of relatively complicated processes, such as genetic mutation, drift and selection (Mcghee 2011). When it comes to man made tools the case is more down to earth, as convergence in the form and function of strictly utilitarian artifacts, such as projectile points, appears usually as an outcome of selection of appropriate traits in order to perform similar tasks. In case of ancient projectile weapon systems, these traits can be for example penetration depth, velocity or aerodynamic characteristics (Hughes 1998; Charlin, Cardillo 2018: pp. 110).
In order to properly identify cases of convergence in primitive projectile technology we ought to look at projectiles and their elements from an evolutionary perspective. This approach implies that archaeological record can be viewed similarly to a way paleobiologists see a fossil bed and that is as a populations of “things”, that represent hard parts (shells, for example) of past phenotypes (Dunnell 1980; Leonard, Jones 1987; Jones et al. 1995; Lyman, O’Brien 1998; O’Brien, Buchanan, Eren 2018). This particular example actually fits very well to what archaeologists have to cope with when reconstructing prehistoric projectile systems, as most often the “soft” parts of weapons, (i.e. their organic elements) are not preserved and usually the only things that remain are stone points.
Biologists see a birds nest, a beavers dam or a twig tool made by a chimpanzee as strictly phenotypic traits (eg. Dawkins 1990; Turner 2000). Archaeological projectile points were also parts of past phenotypes, because they played a signifficant role in gainig food an other resources (see paragrapgh 5) and for this reason their characteristics were shaped by the same evolutionary processes as thosee which influence their makers and users (Leonard and Jones 1987). Consequentially, in this approach artifacts are viewed as an extension of human biological phenotype. It should be emphasized, that this notion of “extended phenotype” is nothing new and it was first introduced to archaeology by O’Brien and Holland (1995) and by Lyman and O’Brien (1998) nearly three decades ago.
In the realm of projectile technology convergence occurs under certain restrictions, which force humans to come up with similar solutions due to the limited range of possibilities (McGhee 2018, pp. 28). In some cases this produces substantial diversity in the construction and morphology of hunting weapons (Serwatka 2018). This phenomenon is often characterized by the occurrence of certain duality in projectiles ranging from heavy, high power ones to light and fast. Heavy projectiles are usually tipped with wide projectile points to enhance the impact force and killing power at short range, while lighter projectiles are tipped with narrow points with sharp tips to facilitate penetration and ensure a precise shot (see Serwatka 2018 and table 1). A weapon system's arrows or darts can be designed to maximize distance or energy based on what is known as the mass/velocity relationship. (Hughes 1998, pp. 370).
The concept of this specific duality in projectile form and function appears earlier in the studies on prehistoric projectile technology and there are several examples of such bimodal projectiles among traditional hunting societies. For instance Cundy (1989) in his study on Australian spearthrowers observed that Aboriginal Australians used either small and light darts, which increased distance of the shot or large and heavy darts, which produced higher energy upon impact and had more killing power.
Similar case, this time in bow and arrow technology, was reported by A.M. and P. Petrequin (1990) among the Danis people living in Western New Guinea. For hunting purposes the Danis use simple arrows tipped with wide bamboo blades. Such construction causes large wounds and shock upon impact, which ensures a quick kill (Petrequin and Petrequin 1990, pp. 492). Conversely, for warfare the Danis prefer more complex and accurate arrows, which can be shot from a considerable distance. The points of these arrows are thin and barbed, which helps with deep penetration and causes complex internal injuries by keeping the point inside the wound (Petrequin and Petrequin 1990, pp. 492).
Another interesting ethnographic example of such duality in the construction of arrows is provided by Griffin (1997), who studied the bow and arrow technology of Agta hunters from North western Luzon. In a dense forest environment characterized by seasonal variation, the Agta hunt with self-bow and arrows. Hunters use a variety of projectile tips, which generally range from large, heavy single-blade tips to light, thin compound tips. (Griffin 1997, pp. 282; see Fig. 4 in this paper.) The selection of the right arrow and projectile point is determined by the size of the prey and the shot's distance. At close range, single-bladed points are utilized. The impact force at close range combined with large and wide points cause shock and sometimes instant death of the prey. The Agta use more precise, multicomponent arrows at fleeing game, when a precise shot from a distance is needed. Points of these multicomponent arrows are connected to the shaft with a piece of string. Additionally, barbs attached to the narrow, sharp points ensure keeping the distal part of the arrow in the wound, which prevents the animal from escaping as the foreshaft and the string becomes entagled in bushes an scrubs when the animal is escaping. (Griffin 1997, pp. 282).
There seem to be several archaeological examples of this duality in the construction of projectiles. Gurina (1956) reports finding different types of arrows in two graves at the Mesolithic cemetary at the Deer Island situated on Lake Onega. The foreshafts of these burials were made of bone and still had lithic points attached to them. In each of these burials, the foreshafts and lithic points were different: 100 grave foreshafts had large, lanceolate points and were straight and smooth (see Fig. 4 in this paper). The foreshafts of grave 118a were shorter and possessed three to four short side barbs. These foreshafts had small, elongated tanged points attached at their distal ends (Gurina 1956).
According to the author’s previous study, Final Palaeolithic Swiderian points were also parts of such bimodal projectile weapon system (Serwatka 2018). Analoguously to the mesolithic points from OleniOstrov, in the Swiderian Culture we are also dealing with wide lanceolate points and considerably lighter and thinner tanged points. These points differ statistically in terms of weight, shape and the character of impact fractures, which strongly suggets that they were parts of such bimodal weapon system (Serwatka 2018).
According to Susan Hughes, when weapons can be manufactured with options for increased distance and high energy, hunting flexibility increases (Hughes 1998, pp. 370). The examples listed above show, that such flexibility in the design of primitive projectiles has the potential of appearing independently in different contexts as an analoguous trait. For a better understanding of this phenomenon it is necessary to look at the problem from the perspective of limitations imposed on primitive projectile technology.
First there are the functional constraints deriving from invariant laws of physics, which are globally universal and independent of ecological conditions, cultural context or time. These include forces such as gravity and drag of the air. All prehistoric hunting societies must have conformed to these restrictions to make their projectiles functional, which means designing them according to basic rules of mechanics and aerodynamics (Cotterell, Kamminga 1992).
Every primitive projectile weapon system is characterized by an insufficient transfer of energy onto a projectile. This particular problem is caused by the construction of simple propulsion mechanisms, such as self bows, which are unable to produce much energy, comparing to modern bows (Klopsteg 1943;Hamilton 1982; Cotterell and Camminga 1992; Hughes 1998). These constraints are strictly technological as they mainly derive from the ignorance of certain methods for making more powerful propulsion devices (eg. Bartram 1997). In a more general sense these restrictions can be viewed as developmental constraints.
Drag increased as a result of the low velocity of prehistoric projectiles, limiting their range and making their trajectory more curved (Cotterell and Kamminga 1992; Burke 1954; Hughes 1998). Since the primary purpose of all hunting weapons is to inflict injuries that would result in the immediate death or immobilization of the prey, this remains a significant limitation of the functionality of primitive projectile weapons. With these restriction in mind, and following McGhee’s scheme of boundaries (Mcghee 2018) we can take a spatial approach in order to visualize basic constraints governing the emergence of such bimodal projectile weapon systems in the area of human technology. Figure 1 shows a spatial representation of two types of constraints imposed on primitive projectile weapons in a theoretical morphospace.
One important conclusion, which derives from the limitations listed above is that primitive hunting weapons were only good enough ata relatively short distance, with the effective range for a self bow reaching approximately 25 meters (Churchill, Rhodes 2009). Hunters often tried to overcome this difficulty by using strategies to approach the game with concealment and disguise or by bringing the game within the effective range (Hitchcock, Bleed 1994; O’Connell, Hawkes 1988; Verbicky-Todd 1984).
A different way of making low velocity weaponry more effective is by manipulating the design characteristics of projectiles themselves in order to improve their key features, such as penetration, killing power and range (Christenson 1986; Hughes 1998). This seems to be the case in the ethnological and archaeological examples given above, where projectiles ranging from high power/short range to low power/long range are developed in order to be better prepared for different hunting situations.
The examples listed above also raise an important taphonomic issue regarding projectile technology in general. As we gradually move on to more ancient examples of bimodal projectile weapon systems we are facing a gradual depletion of data. The Agta or the Danis example provides full insight into the projectile weapon systems function and performance, the Mesolithic example provides only partial information deriving from grave goods (projectile points and foreshafts), and Swiderian points can be interpreted as parts of a projectile weapon system only on the basis of their functional and morphometric features. What links these cases is the appearance of specific bimodal projectiles and points with analogous technological, functional and morphological features (Fig. 2).