Our belief in sea monsters flows from many sources, but stories about them draw at least some of their power from the strange interactions between the human mind, extreme environs and unusual experiences. Put another way, sea monsters occupy the ever-shifting sands where the human subconscious and the physical world meet.
For example, Scylla and Charybdis -- dangerous creatures made famous in Homer's "Odyssey" -- might have been based on real seafaring dangers that sailors faced in the Straits of Messina. Scylla, described as having 12 feet, six heads atop long, sinuous necks, and mouths bristling with rows of sharklike teeth, was said to reach out from her cave to grab and devour any who ventured too close. Charybdis lay on the opposite shore and periodically swallowed and regurgitated the waters there. Some scholars think Scylla represented a dangerous rock or reef, while Charybdis personified a whirlpool [source: Encyclopaedia Britannica].
The unktehila of the Lakota Sioux, Cheyenne, Kiowa and other tribes arose in part from dinosaur bones found by tribal hunters. People in China once venerated the remains of lucky "Guizhou dragons," which turned out to be the bones of 12- to 14-inch-long (30- to 36-centimeter) marine reptiles called Keichousaurus hui [source: Morell].
Similarly, other fabled sea monsters may simply be fish stories -- misremembered or embellished tales of real encounters, either with living creatures at sea or badly deformed and bloated corpses washed up on shore. Sailors might have seen sea serpents in porpoises swimming in a rippling line, in large masses of seaweed or in 30- to 46-foot (9- to 14-meter) basking sharks. And then there's the oarfish, a long, eel-like fish with a red, bristly head crest and long, spiny dorsal fin. These serpentine monsters, which can approach 36-50 feet (11-15 meters) long, swim in an undulating motion that could create apparent "humps" on the sea's surface.
Kraken might well have been based on giant squids, which can reach lengths of 50-70 feet (15-20 meters). A famous legend tells of a sea serpent battling a whale, its mighty arms coiling around the hapless cetacean and dragging it beneath the waves [source: Encyclopaedia Britannica]. This comports with nature, where giant squids are known to tussle with sperm whales, leaving behind sucker and claw scars, or even the odd tentacle for whalers to recovered later from the cetacean's stomach [source: AMNH].
The open ocean is a terrifying, humbling place, and ancient sailors faced a tenuous existence; it was natural to imagine what threats or treasures might dwell, unseen, beneath the surface. Such fancies might have been aided by transitory hallucinations, brought on by misfiring neurons caused by head injury, physical illness, drugs, stress, sleep deprivation, fatigue or mirages [source: Ocean Navigator].
But does that mean that there's no room in the scientific imagination for real sea monsters?