The Magic of Reality Read Online Free PDF Page A

creature ever born belonged to the same species as its grandparents. And its great-grandparents. And its great-great-grandparents. And so on for ever.
    For ever?
Well, no, it’s not as simple as that. This is going to need a bit of explaining, and I’ll begin with a thought experiment. A thought experiment is an experiment in your imagination. What we are going to imagine is not literally possible because it takes us way, way back in time, long before we were born. But
imagining
it teaches us something important.
    So, here is our thought experiment. All you have to do is imagine yourself following these instructions.
    Find a picture of yourself. Now take a picture of your father and place it on top. Then find a picture of his father, your grandfather. Then place on top of that a picture of your grandfather’s father, your great-grandfather. You may not have ever met any of your great-grandfathers. I never met any of mine, but I know that one was a country schoolmaster, one a country doctor, one a forester in British India, and one a lawyer, greedy for cream, who died rock-climbing in old age. Still, even if you don’t know what your father’s father’s father looked like, you can imagine him as a sort of shadowy figure, perhaps a fading brown photograph in a leather frame. Now do the same thing with his father, your great-great-grandfather. And just carry on piling the pictures on top of each other, going back through more and more and more great-great-greats. You can go on doing this even before photography was invented: this is a
thought
experiment, after all.
    How many greats do we need for our thought experiment? Oh, a mere 185 million or so will do nicely!
    Mere?
    MERE?
    It isn’t easy to imagine a pile of 185 million pictures. How high would it be? Well, if each picture was printed as a normal picture postcard, 185 million pictures would form a tower about 220,000 feet high: that’s more than 180 New York skyscrapers standing on top of each other. Too tall to climb, even if it didn’t fall over (which it would). So let’s tip it safely on its side, and pack the pictures along the length of a single bookshelf.
    How long is the bookshelf?
    About forty miles.
    The near end of the bookshelf has the picture of you. The far end has a picture of your 185-million-greats-grandfather. What did he look like? An old man with wispy hair and white sidewhiskers? A caveman in a leopard skin? Forget any such thought. We don’t know exactly what he looked like, but fossils give us a pretty good idea. Believe it or not, your 185-million-greats-grandfather was – a fish. So was your 185-million-greats-grandmother, which is just as well or they couldn’t have mated with each other and you wouldn’t be here.
    Let’s now walk along our forty-mile bookshelf, pulling pictures off it one by one to have a look at them. Every picture shows a creature belonging to the same species as the picture on either side of it. Every one looks just like its neighbours in the line – or at least as much alike as any man looks like his father and his son. Yet if you walk steadily from one end of the bookshelf to the other, you’ll see a human at one end and a fish at the other. And lots of other interesting great- … great-grandparents in between, which, as we shall soon see, include some animals that look like apes, others that look like monkeys, others that look like shrews, and so on. Each one is like its neighbours in the line, yet if you pick any two pictures far apart in the line they are very different – and if you follow the line from humans back far enough you come to a fish. How can this be?
    Actually, it isn’t all that difficult to understand. We are quite used to gradual changes that, step by tiny step, one after the other, make up a big change. You were once a baby. Now you are not. When you are a lot older you’ll look quite different again. Yet every day of your life, when you wake up, you are the same person as when you