The Evolution Of Sharks

Submitted By Kareem Durantula-Abd
Words: 1165
Pages: 5

Hollywood has created an image of sharks that portrays them as senseless killing machines. Many people believe that sharks will attack, and even consume, a human at any chance possible. The more I researched sharks and their behavior, the more I learned that they have been falsely portrayed. Knowing this, I then wanted to learn why it is that sharks attack humans on rare (very rare) occasions. I had grown up assuming that if a shark was nearby, it would most likely attack me. However, I have learned that this is not necessarily true.
Given that there are over 375 different species of sharks, for the most part I will be discussing the White shark, also known as the Great White. With a large dorsal fin, large, triangular serrated teeth, and having gray-black white coloration, the Great White shark can reach up to five meters in length at maturity. The Great White, like all sharks, has a cartilage skeleton. While many species of shark are oviparous (11), the Great White is live bearing (1). Great Whites are predatory animals and generally feed on animals with high quantities of blubber such as sea elephants, sea lions, seals. Often times Great Whites will scavenge on floating carcasses.

Sharks go back through the fossil record about 400 million years, and Great Whites alone have remained unchanged for the last 60 million years (2). Some early species of sharks even predate trees (11). Thus, some physiological characteristics of sharks seem highly evolved, among these being their senses. Sharks' eyesight has been a topic of controversy in the scientific community. It was once believed that sharks have poor eyesight, but studies have shown that sharks' eyes are much more sensitive to light than human eyes, making hunting at night easy. Great Whites have a pair of nostrils, used only for smelling, rather than for breathing. The Great White has an incredible sense of smell that it uses to sniff out prey. Another interesting sense of the Great White is the ampullae of Lorenzini, tiny pores in the skin that are highly sensitive to electrical discharges. These pores can sense charges as little as 0.005 microvolts. This "sixth sense" is useful in tracking prey's movement from long distances (3). In fact, they can feel disturbances in the water from up to a mile away (2).

If Great White sharks have such developed senses, and could eat anything they like, particularly fatty animals why do they attack humans that are relatively low in fat? Little is known about shark behavior, but there are many theories as to why sharks attack humans. Of about 375 species of sharks, only 32 have been documented to have attacked humans, and the three species that have been identified repeatedly in attacks are the great white, tiger, and bull sharks (4).

Sharks, like any animal, will defend themselves if they feel threatened or if they're territory is invaded (5). How a shark will react when threatened ultimately depends on the kind of shark. Many will simply swim away, or some will attack very quickly. The great white tends to attack quickly, catching the victim off guard.

One theory of attack on humans is mistaken identity. Often times divers, surfers, and even kayakers appear like seals or sea lions swimming at the surface of the water. Studies have been done where researches have equipped a surfboard with an underwater camera (6). The camera shows that the great white swims along the bottom of the sea at first, so as not to be seen, then launches a quick, vertical attack. Some scientists believe that great whites do not use their keen sense of sight when hunting prey, but rather, senses a familiar image swimming at the water's surface and assumes it is some kind of prey.

Another theory is that sharks attack as purely inquisitive testing. Researchers say that 96% of all shark attacks are single strikes, or "hit and run" attacks (5).In this type of attack, the shark might bump or slightly graze the victim with the jaws, often times