They have been around for 400 millions of years, and some ancient species have existed before dinosaurs. They have evolved from placoderms, a group of primitive jawed fishes. The average lifespan is 20-25 years, but some, like the dogfish shark can live up to 100 years. They eat plankton, carrion, seals, and/or marine mammals and most (over 75%) of the 345+ species, are not even CAPABLE of the act and/or rarely encounter humans.
On of the misconceptions when dealing with sharks is that they have poor vision. As a matter of fact, its eye is constructed to distinguish colors and is seven times as powerful as a human's. Their corneas have even been used as transplants for human corneas. Next, they do not have to continually move to survive. Some do have to continually move but there are species that do not. Another big myth is that there are no fresh water species, but there ARE. For example the Bull Shark (also know as Zambezi in Africa, Freshwater Whaler, Swan River Whaler and River Whaler in Australia; or Van Rooyen's, Slipway Grey, Square Nose etc.) can function in waters from low salinity (fresh water) to high salinity (salt water). One of the most famous sites of fresh water sharks is a Lake Nicaragua.
Like most large hunters, sharks are slow growing, reach maturity late, and have only a few offspring. Their large young are usually live-born. Unlike most other fish, which can lay thousands of tiny eggs, they produce too few young to compensate for destruction on such a massive scale and their population is greatly depleting. Some species are even considered endangered. In December of 1997, Australia declared endangered the Great White Shark and the Grey Nurse Shark. If the slaughter continues unchecked there is no doubt that we'll lose some species altogether, and others will be reduced to near extinction levels within a few decades.
Sharks have relatively large brains, and can be compared to relatively advanced animals. It's hard to believe, but they can actually be trained. They have also demonstrated a learning rate of the white rat or pigeon. They have been around for millions of years, and some ancient species have existed before dinosaurs. The first shark species appeared 400 million years ago. They have evolved from placoderms, a group of primitive jawed fishes
Sharks are being unnecessarily killed. Through the decades there were very few shark attacks but that did not stop unreasonable fear which, together with commercial (fins, cartilage or other consumer products) or just trophy fishing, is making havoc with shark population. Soon many species will became extinct.