Animal intelligence: Startling new evidence emerges

We've known for some time that apes are brainy. Until a couple of years ago, there had been no observation of gorillas using tools in the wild. Then, in 2005, Thomas Breuer of the Wildlife Conservation Society, while observing lowland gorillas in the Republic of Congo, saw something remarkable. A female gorilla, named Leah, waded upright into a pond until waist deep, and then, unsure of herself, returned to the water's edge, grabbed a stick and proceeded to use it as a depth gauge. Chimpanzees also fashion tools out of twigs, and in tests, one bonobo chimp named Kanzi used a computer to ask him: "Can you make the [toy] dog bite the [toy] snake?" Kanzi found the toys, put the snake in the dog's mouth and squeezed it shut - he understood that "dog" was the subject of the verb "bite" and that the direct object was "snake". Dutch primatologist Carel van Schaik discovered orang-utans do something chimps don't - they use leaves as rain hats and make leak-proof roofs over their nests. The Harvard University psychologist James Lee recently argued that orang-utans are the most intelligent apes of all, knocking chimps off their pedestal - but these findings have yet to be verified. An experiment just reported in the US found that rats are smart enough to know when they don't know something - an ability called metacognition. It was once thought that only humans had this ability, and later it was discovered that some apes have it too. In the recent study, lab rats had to decide whether a sound was short or long. A right answer led to a large food reward; a wrong answer to no reward. But if the rats declined the test, they got a small reward. When the sounds were clearly long or clearly short, discriminating was easy, but when the sounds were of a medium duration, the rats soon worked out that it was better to settle for the small reward, rather than risk an incorrect answer.