In previous research we found that decreases in repertoire diversity could lead to increases in skill level, because a narrower repertoire enables greater skill development per resource type . In Fig. 3 d we show that there is no decline in per capita repertoire diversity as skill levels increase (blue). This indicates that the increase in skill levels occurs via direct effects, where OL enables foragers to shortcut the developmental process by using the experience of other foragers. As a result they can achieve even greater levels of skill than the previous generations. Moreover, given that there is no decrease in per capita repertoire diversity (Fig. 3 d), the increase in repertoire quality implies a replacement, or even addition of high quality resources to the repertoire. We therefore see an increase in skill levels while repertoire diversity is maintained, which means that the overall level and quality of knowledge increases.