Memory is essential for the survival of all animals. They need to remember sources of food and water. In a large forest, a squirrel can remember where it has hidden its nuts. Animals also need to remember how to get to their breeding places. Turtles can remember, over a period of 30 years, the beach on which they were hatched, in order that they may return to the same beach to lay their eggs. Salmon and eels, after crossing the Atlantic, can remember the British rivers where they breed. Swallows, migrating from South Africa, can remember the route to the exact farm in Britain where they built their nest the previous year. The extent of the memory of even quite simple animals is sometimes astonishing. Pinker (1997) cited the example of the Tunisian desert ant, which can travel a distance of 50 metres from its nest, a hole in the sand 1 millimetre across, and ﬁnd its way back. When moved out of position, it will travel the same distance and in the same direction, though obviously, it will not ﬁnd the nest. This demonstrates that it has a way of recording the direction and distance it has travelled.