The young, called pups, are born fully developed and independent. The usual litter size is 2 to 20, but the number of pups may exceed 100. In ovoviviparous species the embryo develops in an egg within the female's body. The young shark hatches while it is still inside the female and then eats any unfertilized eggs. Behavior Information in the second half of the 20th century on shark ecology has provided a better insight into shark behavior.
Most sharks are solitary animals, though a few, such as the spiny dogfish shark, form schools.
Sharks may bite when provoked, but fewer than 30 species are considered dangerous, regardless of the situation. The two largest species, the whale and basking sharks, are harmless plankton feeders. The so-called feeding frenzy, wherein sharks stimulated by the smell of blood feed ravenously and attack any object within reach, is one occasion when different species may be observed together. These feeding frenzies are infrequent. Some authorities doubt whether they occur naturally or only when provoked by humans who supply large quantities of food to attract sharks for studies on feeding behavior.