Figure 1.
Northern Ache maximal boundaries and core use area during the second half of the 20th century.
Bands were distributed throughout the core area, occassionally visiting more remote tribal home range in the Southwest. Band location moved almost daily with no restricted localities. The construction of the road passing through Curuguaty and the core Ache territualory was the impetus for permanent peaceful outside contact in the 1970s. The green square shows the modern day Mbarcayu reserve.
Figure 2.
Eastern Hadza camps where interview subjects and target individuals resided in 2012, with the three regions defined by point color.
In the Center is Lake Eyasi, Tanzania. Satellite image from NASA Earth Observatory.
Table 1.
Characteristics of the Ache and Hadza study samples.
Table 2.
Values for independent variables in dyadic interaction interviews.
Table 3.
Maximum Liklihood Estimates of the beta coefficients for genetic kin (closekin), affinal kin, and ritual relations from equation 1.
Figure 3.
Comparison of the effect of “closekin” and “ritual relationship” on the predicted probability of engaging in specified interaction types.
Each bar represents a the average difference in the probability of interaction calculated as: (P(y)|closekin = 1) – (P(y)|closekin = 0) for “closekin”, and (P(y)|ritual = 1) – (P(y)|ritual = 0) for “ritual relationship”. Probabilities are calculated by averaging values over all dyads while keeping closekin or ritual fixed at 1 or 0, and t = 1. Dark bars represent Ache, light bars represent Hadza.
Table 4.
Proportion of dyads reporting interaction of specified type, and the yearly interaction rate estimated from equation 2, with effects of kinship and ritual relationship controlled.
Figure 4.
Fraction of the adult male standing population that interact at least once over a lifetime plotted by different yearly rates of interaction (p) covering the range of yearly interaction rates listed in Table 4, based on the adult survival table for Ache, Hadza, and Chimpanzees.
The shaded area shows the range of yearly interaction rates of the hunter-gatherer populations.
Figure 5.
Mean change across one generation of social learning, in the cultural adaptiveness of a trait of moderate complexity following Henrich (11: Fig. 3).
The α/β ratio of the model is 5, indicating a moderate mean decrease in cultural adaptedness through initial copy error followed by moderate dispersion of cultural adaptedness (z values) of copiers due to random error and guided innovation. With success-biased imitation, human foragers, with their large number of observed models (range from Table S16 File S1 is indicated), accumulate improvements each generation (Δz>0), whereas chimpanzees, with a smaller number of lifetime interactants are not able to maintain or improve the initial cultural traits (Δz<0).