Alexander Selkirk was a Scottish sailor on whose exploits the story of Robinson Crusoe is based. He went to sea when he was sixteen. Later, he sailed on a pirate ship and after quarreling with the captain, was put ashore, alone, on an island off the coast of Chile in 1704.   He lived on the island alone for 4 1/2 years until he was rescued by a passing ship. The island was heavily populated with rats, which chewed on his feet at night until he made friends with the cat population which took care of his rat problem. There were also goats on the island which provided him with meat and skins with which to make clothing after his wore out. Selkirk's main problem on the island (after the rats were taken care of) was loneliness. In fact, even after he was rescued and returned home to Scotland, he never really recovered from his time on the island. He continued to live alone and built a shelter outside his father's home since he was uncomfortable indoors.   Selkirk went back to sea and died at age 45 of a fever in 1721.