The Science of Discworld II

and we project some of it back into what we think is the outside world. We are conscious only of a small part of its output. These hidden depths and strange associations in the brain may well be responsible for our musical sensibilities.
    Music exercises the mind; it’s a form of play. It seems probable that our liking for music is linked to other things than our ears. In particular, the brain’s motor activity may be involved, as well as its sensory activity. In primitive tribes and advanced societies, music and dance often go together. So it may be the combination of sound and movement that appeals to our brains, rather than one or the other. In fact, music may be an almost accidental by-product of how our brains put the two together.
    Patterns of movement have been common in our world for millions of years, and their evolutionary advantage is clear. The pattern ‘climb a tree’ can protect a savannah ape from a predator, and the same goes for the pattern ‘run very fast’. Our bodies surround us with linked patterns of movement and sound. Like music, they are patterns in time, rhythms. Breathing, the heartbeat, voices in synch with lips, loud bangsin synch with things hitting other things.
    There are common rhythms in the firing of nerve cells and the movement of muscles. Different gaits – the human walk and run, the walk-trot-canter-gallop of the horse – can be characterised by the timing with which different limbs move. These patterns relate to the mechanics of bone and muscle, and also to the electronics of the brain and the nervous system. So Nature has provided us with rhythm, one of the key elements of music, as a side-effect of animal physiology.
    Another key element, pitch and harmony, is closely related to the physics and mathematics of sound. The ancient Pythagoreans discovered that when different notes sounded harmonious, there was a simple mathematical relationship between the lengths of the strings that produced them, which we now recognise as a relation between their frequencies. The octave, for example, corresponds to a doubling of frequency. Simple whole number ratios are harmonious, complicated relationships are not.
    One explanation for this is purely physical. If notes with frequencies that are not related by simple whole numbers are sounded together, they interfere with each other to produce ‘beats’, a jarring low-frequency buzz. Sounds that make the sensory hairs in our ears vibrate in simple patterns are necessarily harmonious in the Pythagorean sense, and if they aren’t, we hear the beats and they have an unpleasant effect. There are many mathematical patterns in musical scales, and they can be traced, to a great extent, to the physics of sound.
    Overlaid on the physics, though, are cultural fashions and traditions. As a child’s hearing develops, its brain fine-tunes its senses to respond to those sounds that have cultural value. This is why different cultures have different musical scales. Think of Indian or Chinese music compared to European; think of the changes in European music from Gregorian chants to Bach’s Well-Tempered Clavier .
    This is where the human mind is situated: on the one hand, subject to the laws of physics and the biological imperatives of evolution; on the other, as one small cog in the great machine of human society. Our liking for music has emerged from the interaction of these two influences. This is why music has clear elements of mathematical pattern, but is usually at its best when it throws the pattern book awayand appeals to elements of human culture and emotion that are – for now, at least – beyond the understanding of science.
    Let’s come down to Earth and ask a simpler question. The wells of human creativity run deep, but if you take too much water from a well it runs dry. Once Beethoven had written the opening bars of his Symphony in C Minor – dah-dah-da DUM – that was one less tune for the rest of us. Given the amount of music that has been composed over the ages, maybe most of the best tunes have been found already. Will the composers of the future be unable to match those of the past because the world is running out of tunes?
    There is, of course, far more to a piece of music than a mere tune. There is melody, rhythm, texture, harmony, development … But even Beethoven knew you can’t beat a good tune to get your composition off the ground. By ‘tune’ we