The Science of Discworld II

mind, let alone what that feels like to them. Each human mind is wired differently, and is the product of its owner’s own experiences. It is even more problematic whether we can imagine what it is like to be an animal. On Discworld, an accomplished witch can put herself inside an animal’s mind, as we see, for instance, in this passage from Lords and Ladies :
    She Borrowed. You had to be careful. It was like a drug. You could ride the minds of animals and birds, but never bees, steering them gently, seeing through their eyes. Granny Weatherwax had many times flicked through the channels of consciousness around her. It was, to her, part of the heart of witchcraft. To see through other eyes …
    â€¦ through the eyes of gnats, seeing the slow patterns of time in the fast pattern of one day, their minds travelling rapidly as lightning …
    â€¦ to listen with the body of a beetle, so that the world is a three-dimensional pattern of vibrations …
    â€¦ to see with the nose of a dog, all smells now colours …
    It’s a poetic image. Does a dog ‘see’ smells? There is a folk belief that smell is far more important to a dog than sight, but this could well be an exaggeration based on the more credible observation that smell is more important to dogs than it is to humans. But even here we must add ‘consciously, at least’, because we react subconsciously to pheromones and other emotionally loaded chemicals. Some years ago David Berliner was working on the chemicals in human skin, and he left an open beaker containing some skin extracts on the laboratory bench. Then he noticed that his lab assistants were becoming distinctly more animated than usual, with a lot of camaraderie and mild flirtation. He froze the extract and put it away in the laboratory refrigeratorfor safekeeping. Thirty years later, he analysed the substances in the beaker and found a chemical called androstenone, which is rather like a sex hormone. A series of experiments showed that this chemical was responsible for the animated behaviour. However, androstenone has no smell. What was going on?
    Some animals possess a ‘vomeronasal’ organ (often called the ‘second nose’). This is a small region of tissue in the nose, which detects certain chemicals but is separate from the standard olfactory (smelling) system. The conventional wisdom had long been that humans do not possess a vomeronasal organ, but the curious behaviour of his assistants made the scientist wonder. Berliner discovered that the conventional wisdom was wrong: some humans, at least, do have a vomeronasal organ, and it responds to pheromones. Those are special chemicals that trigger strong responses in animals, such as fear or sexual arousal. The vomeronasal organ’s owners are not consciously aware that they are sensing anything, but boy, do they respond.
    This story shows how easily we can get sensations wrong. In this case, you know what it vomeronasally smells like to be a human: you don’t feel anything at all, not consciously. But you certainly respond! So your reactions, and what they ‘feel like’, are very different. The sounds we hear, the sensations of heat and cold on our skin, the smells that assail our nostrils, the unmistakable taste of salt … all these are qualia, vivid ‘feelings’ stuck on to our perceptions by our minds to help us recognise them more readily. They have a basis in reality, yes, but they are not real features of the outside world. They must be real features of brain architecture and function, real things happening in real nerve cells, but that level of reality is very different from the level that we perceive.
    So we should be suspicious of the belief that we can know what it feels like to be a dog. In 1974 the philosopher Thomas Nagel published a famous essay ‘What is it like to be a bat?’ in the Philosophical Review , in which he made the same point. We can imagine what it is like to be a human who is behaving – superficially at least – like a bat, but we have no idea what it feels like to the bat , and it is questionable whether human knowledge can ever extend in such a direction.
    We probably get bats wrong anyway. We know that bats use echo-locationto sense their surroundings, much as a submarine uses sonar. The bat or submarine emits sharp pulses of sound, and hears the returning echoes. From those, it can ‘compute’ what the sound