IDEAS: Elephants have different ideas to our own - but that doesn't make them dumb.

Animal intelligence has been badly underestimated, partly because of the way humans have tried to measure it, a prominent primatologist says.

In an article in The Wall Street Journal, Frans de Waal said the problem of how to give an animal an IQ test was one of the thorniest questions facing science.

Findings by researchers who had come up with some ingenious solutions to the testing problem in the past decade had started to upend a view of mankind's unique place in the universe that dated back at least to ancient Greece, he said.

For example, scientists had believed elephants were unable to use tools. Elephants had been offered long sticks to reach food placed outside their reach but left the sticks alone, leading researchers to conclude the animals did not understand the problem.

But elephants used their trunks not only to reach food but also to sniff and touch it with their unparalleled sense of smell.

For elephants, vision was secondary, but as soon as they picked up a stick their nasal passages were blocked, and their feeding and smelling were impeded, de Waal said.

Another way of testing had been tried with an elephant called Kandula at the National Zoo in Washington DC. Scientists hung fruit just too high for Kandula to reach, then gave the elephant several sticks and a sturdy square box.

Kandula ignored the sticks but, after a while, started kicking the box with his foot, kicking it many times in a straight line until it was underneath the branch. He then stood on the box with his front legs and was able to reach the food with his trunk.

Kandula had also without hesitation fetched the box from elsewhere in the yard, out of view, to get the fruit. To do so he had needed to recall the solution and walk away from his goal to fetch the tool, which few animals would do, apart from large-brained species such as humans, apes and dolphins, de Waal said.

It may also be necessary to rethink how animal intelligence functioned. For example, octopuses seemed to "think, literally, outside the box of the brain".

Octopuses had hundreds of suckers, each with its own ganglion with thousands of neurons. Those "mini-brains" were interconnected, making for a widely distributed nervous system, which was why a severed octopus arm may crawl on its own and even pick up food.

Similarly, when an octopus changed skin colour, the command may come from the skin.

Gene sequences that were similar to those in the eye's retina had been found in the skin of cuttlefish.

"Could it be: an organism with a seeing skin and eight thinking arms?" de Waal said.

Another issue arose when efforts were made to try to establish how smart apes were relative to children.

Scientists would present both species with identical problems, but the children were held by their parents and spoken to. By contrast, the apes sat behind bars, did not benefit from language or a nearby parent who knew the answers, and were facing members of a different species.

A recent study tracking the pupil movements of chimpanzees found they followed the gaze of members of their own species far better than that of humans.

That finding had huge implications for tests in which chimps needed to pay attention to a human experimenter, de Waal said.

The question of whether a human or an ape was smarter depended on the task.

In a 2007 study, Ayumu, a young male chimp at Kyoto University in Japan, had put human memory "to shame".

Trained on a touch screen, the chimp could recall a random series of nine numbers, from one to nine, and tap them in the right order, even though the numbers had been displayed for just a fraction of a second.

Ayumu had outperformed a group of university students by a wide margin and beaten the British memory champion.