Why is tool use rare in animals?

Tool use is widespread in the animal kingdom. It has been reported in taxa ranging from insects to primates (see reviews in Beck, 1980; Bentley-Condit & Smith, 2010; Shumaker <italic>et al</italic>., 2011). However, although it is taxonomically widespread, tool use is relatively rare. The rarity of tool use is surprising given the potential evolutionary advantages that a species can gain. Tools can be used to extract rich food sources such as termites and wood-boring larvae that would otherwise be extremely difficult to obtain. Given the obvious advantages of tool use, an equally obvious question is why tool use is seen in very few species. A glance across the species that use objects as tools rules out any simple association between the presence or absence of tool use and level of cognitive ability. Tool use is seen in insects, marine invertebrates and fish, as well as in birds and mammals. Indeed, Jane Goodall (1970) recognized that the evolutionary processes underpinning tool use across the animal kingdom will be very different. Beck (1980) emphasized that there was no simple correlation between the presence of tool use and cognitive abilities. Hansell and Ruxton (2008) recently proposed another possible explanation for the rarity of tool use in animals – that tool use was rare simply because of the lack of ecological contexts in which it was advantageous (we call this the lack-of-utility hypothesis). However, we will show here that an “excess of opportunity” clearly contradicts the lack-of-utility hypothesis because in evolutionary terms tool use appears to be potentially much more useful than its frequency in the animal kingdom indicates.