Is consciousness unique to us or are animals also conscious of their existence? In her latest book Through Our Eyes Only? Mario Stamp Dawkins, a lecturer at Oxford University, makes a careful case for the conscious chicken, marshalling evidence from years of research into the way chickens behave.

Her main hypothesis is this: If consciousness has evolved, "it must make a difference to how an organism behaves." Dawkins believes you don't have to be smart to be conscious--just emotional (a dumb chicken could as conscious as a clever chimpanzee). "It has to matter to you whether the world is one way rather than another, and you have to be willing and able to work to achieve your preferred state or situation."

Dawkins starts with the premise that if animals have feelings they must be able to act on them. She pioneered the idea of :sking' an animal how much some resource mattered to it, by making the animal work to achieve it. For instance, she trained her hens to peck a key to gain access to a nest box and then upped the ante, so that the bird eventually had to peck the key 50 times to achieve the same end. In this way Dawkins could find out how hard the birds were willing to work--how much it mattered.

This and similar experiments with henpecked hens has led Dawkins to conclude that if hens can show they would rather the world were one way than another, then they have subjective experiences at least partly comparable to our own.