An experiment using, a packet of sweets and a computer suggests that pigs may be the smartest animals on Earth. Tim Cornwell reports

The American Society for the Prevention of Cruelty to Animals has already offered good homes to Hamlet and Omelette, two large white pigs currently under the care of Stanley Curtis. Professor Curtis generally likes a nice piece of pork; but for this particular porcine duo, he is making an exception.

Hamlet and Omelette surely deserve a comfortable retirement. Curtis's treatment of them over the past few months has not been physically cruel. But they have been mentally taxed to the limit. In simple terms, Curtis claims to have taught them to play primitive computer games with a joystick.

Curtis is not the first to believe that pigs are intelligent. Witness George Orwell, or author Dick King-Smith, whose experience as a pig farmer inspired him to write the story of Babe - a tale of a thinking pig who switched career paths to herd sheep. But Curtis claims his research shows that pigs are faster learners than chimpanzees. It potentially qualifies them as the smartest animals on the planet, if not - yet - as our own mental equals.

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Curtis earned his doctorate in animal sciences in 1968. Since then, while he briefly helped train a zoo elephant, his work at Pennsylvania State University has been mostly in the design and management of animal facilities - particularly piggeries. "The stressed pig of today is the sick pig of tomorrow," he observes. His concern was to make the animals as comfortable as possible. For pigs that are almost hairless, picking the right temperature, and avoiding draughts and cold surfaces, is vital.

More than 20 years ago, Cambridge University's Bob Baldwin discovered that pigs in a chilly environment would press a lever to deliver heat. Curtis, using the same method, went on to reveal that pigs, in groups, will typically allocate one of their number to adjust the heat source. He also found that they liked lower temperatures at night. It helped piggeries make a considerable saving in energy costs, he said.

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In his new research, however, he is seeking to learn more directly what pigs like and dislike - hoping he can train them to express themselves through a computer. Curtis himself first showed Hamlet and Omelette how to move the joystick, and he and his student assistants lured them to the object with M&Ms, the American equivalent of Smarties. The researchers assumed the pigs would move the joystick with their snouts. In fact, they grasped it in their teeth.

The first "game" involved moving the cursor from the centre of the 13-inch screen to anywhere on the border. The reward for each success was an M&M. For sceptics who think that any dumb animal could achieve this by grabbing the joystick and chewing it, the target became progressively smaller: first three sides, then two, one, then a one-inch square anywhere on the screen. Curtis reports an 80 per cent success rate.

The six-month-old pigs, he is certain, related the movement of the joystick to the cursor on the screen. When their attention was flagging, his students would admonish them, saying "are you watching the screen?" The pigs would deliberately turn their heads so that one eye was right against the monitor, he said. "It was almost a sarcastic, smart-alecky response."

So far, the pigs are nowhere near the reported understanding of chimps, who in US trials have successfully tackled considerably more complex computer games. But while Curtis stresses his experiments are in the embryonic stage, he insists the pigs' learning rate on the tests so far is faster than that of the primates. While their concentration span appears shorter, only about 15 to 20 minutes compared to the hour or so that chimps will linger in front the machines, their learning is more intense, he said. He attributes their tendency to wander away to the 300lb weight on their trotters. "One of the reasons they may need to move around and leave the joystick is because their feet are sore," he said.

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Hamlet and Omelette are soon to stand aside for a new batch of pigs, partly because they are showing signs of boredom and laziness. Armed with his first results, he is determined to take the next lot of animals to a more challenging level. "I don't believe that we are in any way near their maximum cognitive capacity," he said.

Farmers may feel wary about demonstrations of pigs' intelligence - Westerners do not generally eat dolphins or dogs, after all. But while Curtis says his aim is to establish rudimentary communication with the animals, he is quite unsentimental about the ultimate purpose of his research. He freely admits that he wants to learn more about them, chiefly to improve conditions for their short stay on this earth en route to the slaughter-house. Sounds like another case of "four legs good, two legs bad".

Stanley Curtis will appear on QED, BBC1 on June 3 at 10pm.