As adults, we are heavily influenced by the culture in which we grow up; and there is no question that human children learn elements of culture from others. Thus, an important open question is at what age - and how - children accumulate the culture of their peers. Some great ape tool use has been proposed as a case of cumulative culture, too. But it may be that the great apes do not acquire their tool use via the same learning mechanisms as human children. For example, great apes may basically re-invent the techniques required for efficient tool use for themselves after observing the outcomes of others actions (i.e., "re-inventing the wheel"). Whether they really do so, is again an open question. Tennie's work during this grant is aimed to provide answers to these questions: it will determine the necessary learning mechanisms for cumulative culture (by testing human children) and it will determine if great apes can "re-invent the wheel" (by providing naive subjects with the raw material for the tools currently claimed to be cumulative culture).