If chimps had history books, a few individuals would have important chapters devoted to them. One would be David Greybeard, the chimp who in 1960 was observed by Jane Goodall using a piece of grass as a tool.

Another would be Ai, the female chimp currently living at the Primate Research Institute in Kyoto. Ai has shown incredible understanding of language, and extraordinary memory.

Both David Greybeard and Ai have made headlines — the former for overturning the belief that only humans had the ability to use tools, and the latter for giving us an insight into the intellectual richness of the chimp mind. They have forced us to take fresh looks at what we assume about animal behavior.