Where would people be without magnetic compasses? The short answer is: lost. By giving human beings a sixth sense-an ability to detect the hitherto invisible magnetic field of the Earth-the compass proved one of the most important inventions ever. It let sailors navigate without sight of the night sky. And that led to the voyages of discovery, trade and conquest which created the political geography of the modern world. Imagine, then, what animals which had their own, built-in compasses could achieve. They might spend their summers doing the English Season in Glyndebourne or Henley, and then overwinter in the warmth of Mombasa. They might strike out, like intrepid pioneers, from Angola to Anchorage. They might even, if truly gripped by wanderlust and a hatred of the darkness, live in near-perpetual daylight by migrating from Pole to Pole.
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