Shark Image Gallery
Shark Image Gallery

An Australian customs officer displays drying shark fins found on board a suspected illegal fishing boat near Darwin, Australia. See more shark pictures.

Handout/Getty Images

Sharks have been swimming in the Earth's oceans for about 400 million years. They predate humans, dinosaurs and just about anything that walks, crawls or swims. The average shark lives to be about 25, and it's believed that some sharks can live up to 100 years or more. This places them next to the whale as one of the longest-living sea creatures. The fact that they have such a long lifespan has prompted a great deal of research into the secret to their longevity.

Sharks have been studied closely for more than 100 years, mainly because of their low likelihood of contracting disease. Fish with bones have a pretty high rate of growing tumors. For a long time, scientists believed that sharks were immune to cancer and tumors. So what makes sharks different? They don't have bones. Their skeleton is made up entirely of cartilage. This is one reason that shark teeth are collectible -- it's the only fossil you can find from dead sharks. Their cartilage dissolves over time, and nothing is left but the hard-enameled teeth. Many researchers think that this cartilage holds the secret to the cure for some human medical conditions -- namely cancer.

The shark-cartilage industry is booming, to say the least -- some statistics place earnings at about $25 million per year [source: McGraw Hill]. Most of this money comes from the sale of over-the-counter supplements and vitamins containing shark cartilage. You can walk into any health supplement store or browse the Internet and find dozens of shark-cartilage products. It's typically sold in powdered form or packaged in an oral capsule. It's estimated that 100 million sharks are killed every year by humans. We can't know for sure how many are killed for their cartilage, but the vast amounts of shark products on the market give us a pretty good idea.

But could sharks really help cure disease? And can they aid in the fight against cancer? We'll get to the bottom of these questions on the following page.

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