RUPERT SHELDRAKE is a biologist living in London. His latest book is The Sense of Being Stared At: And Other Aspects of the Extended Mind.
We don’t understand animal navigation.
No one knows how pigeons home, or how swallows migrate, or how green turtles find Ascension Island from thousands of miles away to lay their eggs. These kinds of navigation involve more than following familiar landmarks or orienting oneself in a particular compass direction; they involve an ability to move toward a goal.
Why is this current ignorance of ours dangerous? Don’t we just need a bit more time to explain that navigation in terms of standard physics, genes, nerve impulses, brain chemistry? Perhaps.
But there is a possibility that animal navigation may not be explicable in terms of present-day physics. Over and above the known senses, some species of animals may have a sense of direction that depends on their being attracted toward their goals through direct, fieldlike connections. These spatial attractors are places with which the animals themselves are already familiar or with which their ancestors were familiar.
What are the facts? We know more about pigeons than any other species. Within familiar territory, especially within a few miles of their home, pigeons can use landmarks; for example, they can follow roads. But using familiar landmarks near home cannot explain how racing pigeons return across unfamiliar terrain from six hundred miles away, even flying over the sea, as English pigeons do when they are raced from Spain.
Charles Darwin, himself a pigeon fancier, was one of the first to suggest a scientific hypothesis for pigeon homing. He proposed that they might use a kind of dead reckoning, registering all the twists and turns of the outward journey. This idea was tested many years later, by taking pigeons away from their lofts in closed vans by devious routes. They still homed normally. So did birds transported on rotating turntables. So did birds that had been completely anesthetized during the outward journey.
What about celestial navigation? One problem for hypothetical solar or stellar navigation systems is that many animals continue to navigate in cloudy weather. Another problem is that celestial navigation depends on a precise time sense. To test the sun navigation theory, homing pigeons were clock-shifted by six or twelve hours and taken many miles from their lofts before being released. On sunny days, they set off in the wrong direction, as if a clock-dependent sun compass had been shifted. But they soon corrected their course and flew homeward normally.
Two main hypotheses remain: smell and magnetism. Smelling the home position from hundreds of miles away is generally agreed to be implausible. Even the most ardent defenders of the smell hypothesis (the Italian school of Floriano Papi and his colleagues) concede that smell navigation is unlikely to work at distances over thirty miles.
That leaves a magnetic sense. A range of animal species, including termites, bees, and migrating birds, can detect magnetic fields. But even if pigeons have a compass sense, this cannot by itself explain homing. Imagine that you are taken to an unfamiliar place and given a compass. You will know from the compass where north is, but not where home is.
The obvious way of dealing with this problem is to postulate complex interactions between known sensory modalities, with multiple backup systems. The complex-interaction theory is safe, sounds sophisticated, and is vague enough to be irrefutable. The idea of a sense of direction involving new scientific principles is dangerous, but it may be inevitable.