Tool use, aye-ayes, and sensorimotor intelligence

Humans, chimpanzees, capuchins and aye-ayes all display an unusually high d egree of encephalization and diverse omnivorous extractive foraging. It has been suggested that the high degree of encephalization in aye-ayes may be the result of their diverse, omnivorous extractive foraging behaviors. In c ombination with certain forms of tool use, omnivorous extractive foraging h as been hypothesized to be linked to higher levels of sensorimotor intellig ence (stages 5 or 6), Although free-ranging aye-ayes have not been observed to use tools directly in the context of their extractive foraging activiti es, they have recently been reported to use lianas as tools in a manner tha t independently suggests that they may possess stage 5 or 6 sensorimotor in telligence. Although other primate species which display diverse, omnivorou s extractive foraging have been tested for sensorimotor intelligence, aye-a yes have not. We report a test of captive aye-ayes' comprehension of tool u se in a situation designed to simulate natural conditions. The results supp ort the view that aye-ayes do not achieve stage 6 comprehension of tool use , but rather may use trial-and-error learning to develop tool-use behaviors . Other theories for aye-aye encephalization are considered.