The flexible, the stereotyped and the in-between: putting together the combinatory tool use origins hypothesis.

Tool use research has long made the distinction between tool using that is considered learned and flexible, and that which appears to be instinctive and stereotyped. However, animals with an inherited tool use specialisation can exhibit flexibility, while tool use that is spontaneously innovated can be limited in its expression and facilitated by predispositions for ecological specialisations. Furthermore, recent evidence does not support the proposed division of flexible tool use along primate-bird taxonomic lines. Instead, we hypothesise that tool use is a more complementary phenomenon than previously believed, in that the intrinsic motivation for combinatory object manipulation underlies the onset of all allocentric tool use, resulting in a spectrum. What influences the initial tool use that does emerge is the form of a species' object combinations, which is itself influenced by ecological niche. Therefore, an opportunistic extractive forager will likely develop more diverse forms of tool use than a specialist.