As expected, we find that when OL generates a cumulative cultural increase in energy levels, this is accompanied by a cumulative cultural increase in skill level (Fig. 3 d). In Fig. 3 d we can observe that OL at H=10 leads to a large increase in skill level. We find that next to increases in skill, OL at H=10 also leads to cumulative cultural increases in repertoire quality (Fig. 3 d). Thus the increases in energy intake result from both increases in skill level and repertoire quality.