Modeling a primate technological niche

Abstract

The ability to modify the environment through the transport of tools has been instrumental in shaping the evolutionary success of humans. Understanding the cause-and-effect relationships between hominin behavior and the environment ultimately requires understanding of how the archaeological record forms. Observations of living primates can shed light on these interactions by investigating how tool-use behaviors produce a material record within specific environmental contexts. However, this requires reconciling data derived from primate behavioral observations with the time-averaged nature of the Plio-Pleistocene archaeological record. Here, we use an agent-based model to investigate how repeated short-distance transport events, characteristic for primate tool use, can result in significant landscape-scale patterning of material culture over time. Our results illustrate the conditions under which accumulated short-distance transport bouts can displace stone tools over long distances. We show that this widespread redistribution of tools can also increase access to tool require resources over time. As such, these results elucidate the niche construction processes associated with this pattern of tool transport. Finally, the structure of the subsequent material record largely depends on the interaction between tool transport and environmental conditions over time. Though these results have implications for inferring hominin tool transports from hominin archaeological assemblages. Furthermore, they highlight the difficulties with connecting specific behavioral processes with the patterning in the archaeological record.

Figure 1

A two-way plot illustrating the effect of the number of Trees and number of Sources on the maximum distance Pounding Tools move from its source. An ordinary least squares regrsssion shows that the number of Sources and Trees have a positive effect on the distances Pounding Tools can be moved (R²: 0.76). The number of Sources has a marginal but significant effect on the maximum distances Pounding Tools move but this effect increases with the number of Trees (p-value < 0.0001). Increasing the number of Trees has a much greater effect on the maximum distance a Pounding Tool can move from its Source (p-value < 0.0001). The points represent the specific values associated with each iteration for a given parameter combination.

Figure 2

The number of tool-use locations per time-step through time when the number of Sources is 500 (high-density) and the number of Trees is 2000 (high-density). The number of tool-use locations increases (y-axis) due to the repeated displacement of Pounding Tools away from their Sources. (A) Tree locations do not change through time. (B) Tree locations change through time (see text). Each line represents an individual iteration of the model. Under these conditions, the number of tool-use locations plateaus at a higher value when Trees change locations over time. It is expected that the number of Trees that become accessible for tool use would eventually reach the maximum number of Trees in the model. However, this remains unclear given that the simulation ended at 75,000 time-steps.

Figure 3

(a) The archaeological record when there are 100 Sources and 100 Trees. Notice that the subsequent archaeological record forms extremely localized patches of material. (b) The material record when there are 100 Sources and 2000 Trees. This material record is becoming more widespread but remains localized. (c) The archaeological record when there are 100 Sources and 2000 Trees where Tree locations change over time. Notice how the material record becomes substantially more widespread under these conditions.

Figure 4

(A) Scatter plot showing the relationship between the number of usable Pounding Tools contained within a single grid cell with the distance to the nearest Source. Since grid cells are not associated with a Source their relationship to Sources is expressed as the minimum distance. (B) The relationship between usable Pounding Tool size (grams) and distance to its Source. (C) The effect of the environment on the proportion of grid-cells where Pounding Tools are represented within an individual assemblage. Increasing the number of Sources increases the percentage of assemblages that contain Pounding Tools. Increasing the number of Trees or allowing the Trees to change locations substantially reduces the proportion of assemblages that contain useable tools (See SOM Fig. S8). Plots (A) and (B) show run where the number of Sources is 100, the number of Trees is 2000 and Trees can change location. See SOM Figs. S5, S6, and S7 for other parameter combinations.