People have identified with dolphins for thousands of years. Several early accounts from the Mediterranean area tell of children riding on dolphins. According to the Roman scholar Pliny the Elder, a boy from Lake Lucrino, near Naples, made friends with a dolphin that carried him across the water to school every day. Another boy, from Hippo (now part of Tunisia), became friends with a dolphin after the dolphin saved him from drowning. These stories, thought to be true, were written almost 2,000 years ago, in the first century A.D.

Christina Lockyer of the Sea Mammal Research Unit in England investigated these as well as modern-day cases of "friendly," sociable dolphins. She took to the water and swam with dolphins - and went for many rides herself. She was able to confirm various reports of encounters between friendly dolphins and humans:

- In the mid-1950s, in New Zealand, a young female bottlenose dolphin became friendly with swimmers, both children and adults. Opo, as she was called, allowed people to sit on her back while she moved slowly through the water.

- In the 1960s, in Monkey Mia, Australia, a woman began feeding and touching a group of bottlenose dolphins that regularly came into the shallows, in water less than one metre deep. From 1966 to 1972, a dolphin known as Old Charlie became so familiar, he permitted children to sit on his back. Today, 100,000 people a year come to wade into the water to meet and touch the dolphins. People offer them dead fish, which the dolphins either eat, play with or ignore. Only some of the dolphins swim in - seven regulars, by the most recent count. The others remain out in the bay.

- In the 1960s, a female bottlenose dolphin befriended a family in Florida. After two months, Georgy Girl seemed to be encouraging the family to touch her and began carrying people on her back after swimming between their legs.

- In 1981, an older 4.1-metre male bottlenose dolphin named Percy began following a fishing boat on its daily run off Cornwall, England. After almost two years, he allowed people to touch him, hang on to his dorsal fin and go for rides. But then he became unpredictable. Sometimes, he was gentle, but at other times, he would butt swimmers in the chest, smash surfboards and carry people out to sea. It was a reminder that wild animals should be approached with caution. Since then, some scientists have begun to question the wisdom of taming or making friends with wild dolphins.

Which dolphin species are "sociable"? Most are bottlenose dolphins, although orcas, Risso's dolphins and others have also participated in such encounters. The gregarious dolphins tend to be either old or young animals. In each case, the dolphins have revealed individual personalities. Many have been solitary creatures, but exceptions include the regulars at Monkey Mia. Perhaps there are various reasons for accepting humans as temporary social companions. All seem to have had a history of persistent taming by one or more people over a period of months or years. Only a few of the dozens of cases - notably Percy and another dolphin, called Donald - became aggressive to the point of being dangerous to humans. Both were older male bottlenose dolphins whose activities off Britain's coast were closely monitored by Lockyer and others.

The best explanation for such behavior might simply be that bottlenose dolphins, as well as other dolphins, are intensely curious. such curiosity is a necessary part of being an opportunistic predator. It can be crucial to the dolphin's survival to check out new additions to its environment. In every case reported here, a curious and close approach to a human was repeatedly encouraged, and the dolphin responded. In time, the animals get used to human company. What seemed to be play behavior was the result. The dolphins may somehow have been trying to incorporate people into their group.

Some scientists have worked with these tamed dolphins, engaging them as partners in their research, testing their audio and diving abilities and swimming speeds. Eventually, however, the dolphins disappear, leaving the researchers to ponder the mysteries of sociable dolphins - why they come and why they go.

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