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Whales are the largest Species of exclusively aquatic Mammal s, members of the Order ''' Cetacea ''', which also includes Dolphins and Porpoises . They include the largest known animals ever evolved. The term ''whale'' is ambiguous: it can refer to all cetaceans, to just the larger ones, or only to members of particular Families within the order Cetacea. The latter definition is the one followed here. Whales are those cetaceans which are neither dolphins (i.e. members of the families Delphinidae or Platanistoidea ) nor Porpoise s. This can lead to some confusion because Orca s ("Killer Whales") and Pilot Whale s have "whale" in their name, but they are dolphins for the purpose of classification. breaching]] ORIGINS AND TAXONOMY Whales, along with most dolphins and porpoises, are descendants of land-living mammals, most likely of the Artiodactyl Order . They entered the water roughly 50 million years ago. See Evolution Of Cetaceans for the details {Link without Title} . Cetaceans are divided into two suborders:
A complete up-to-date taxonomical listing of all cetacean species, including all whales, is maintained at the Cetacea article. ANATOMY Like all mammals, whales breathe air into Lungs , are Warm-blooded , breast-feed their young, and have some (although very little) hair. The whales' ancestors lived on land, and their adaptions to a fully aquatic life are quite striking. The body is fusiform, resembling the streamlined form of a fish. The forelimbs, also called flippers, are paddle-shaped. The end of the tail holds the fluke, or tail fins, which provide propulsion by vertical movement. Although whales generally do not possess hind limbs, some whales (such as Sperm Whale s and Baleen Whale s) sometimes have rudimentary hind limbs; some even with feet and digits. Most species of whale bear a fin on their backs known as a Dorsal Fin . Beneath the Skin lies a layer of Fat , the Blubber . It serves as an energy reservoir and also as insulation. Whales have a four-chambered Heart . The neck Vertebrae are fused in most whales, which provides stability during swimming at the expense of flexibility. Whales breathe through Blowholes , located on the top of the head so the animal can remain submerged. Baleen Whale s have two; Toothed Whale s have one. The shapes of whales' spouts when exhaling after a dive, when seen from the right angle, differ between species. Whales have a unique respiratory system that lets them stay underwater for long periods of time without taking in oxygen. Some whales, such as the Sperm Whale , can stay underwater for up to two hours holding a single breath. The Blue Whale is the largest known animal that has ever lived, at up to 30 m (93ft) long and 180 tons. BEHAVIOUR ''Main article: Whale Behaviour '' Whales are broadly classed as Predator s, but their food ranges from microscopic plankton to very large fish. Males are called bulls; females, cows. The young are called calves. Because of their environment (and unlike many animals), whales are conscious breathers: they decide when to breathe. All mammals Sleep , including whales, but they cannot afford to fall into an unconscious state for too long, since they need to be conscious in order to breathe. It is thought that only one hemisphere of their brains sleeps at a time, so that whales are never completely asleep, but still get the rest they need. Whales are thought to sleep around 8 hours a day. Whales also communicate with each other using lyrical sounds. Being so large and powerful these sounds are also extremely loud and can be heard for many miles. They have been known to generate about 20,000 acoustic watts of sound at 163 decibels. See Table of sound decibel levels . Females give birth to a single calf. Nursing time is long (more than one year in many species), which is associated with a strong bond between mother and young. In most whales reproductive maturity occurs late, typically at seven to ten years. This strategy of reproduction spawns few offspring, but provides each with a high rate of survival. The genital organs are retracted into cavities of the body during swimming, so as to be streamlined and reduce drag. Most whales do not maintain fixed partnerships during mating; in many species the females have several mates each season. At birth the newborn is delivered tail-first, so the risk of drowning is minimized. Whale mothers nurse the young by actively squirting the fatty milk into their mouths, a milk that according to German naturalist Dieffenbach , bears great similarities to cow's milk. Biologists compare the consistency of whale milk to cottage cheese; it must be thick, or else it will dissipate into the surrounding water. WHALE INTELLIGENCE ''For more material in this area, focusing more on Dolphins , see Cetacean Intelligence ''. Many people believe that cetaceans in general, and whales in particular, are highly Intelligent animals. This belief has become a central argument against Whaling (killing whales for food or other commercial reasons). There is no universally agreed definition of "intelligence." One commonly used definition is "the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience." Proponents of whale intelligence cite the social behavior of whales and their apparent capacity for language as evidence of a sophisticated intellect. Given the radically different environment of whales and humans, and the size of whales compared to Dolphin s or Chimpanzee s, for instance, it is extremely difficult to test these views experimentally. One traditional indicator of intelligence is Brain capacity, since humans have bigger brains than most other animals. Whales have the largest brain of any animal. A typical sperm whale brain weighs about 7.8 kg, whereas a typical human brain weighs about 1.5 kg. While it may seem that this would indicate that five times greater intelligence, in mammals brain size is in approximate ratio to body size, and most of the extra capacity is used to manage the larger body. A more precise indicator is the brain-body ratio: the size of the brain compared to body mass. Here humans have a decisive advantage. A human brain comprises about 2% of the human body mass, while the sperm whale's brain comprises only 0.02% of its body mass. A Cow 's brain is four times as large as a whale's on this measurement. On the other hand, a large proportion of a whale's body mass is Blubber , which requires no brain power, and this distorts the ratio somewhat. Nevertheless, it is clear that brain size is not a decisive criterion. Hummingbirds have an even higher brain-to-body ratio than humans. The next consideration is the structure of the brain. It is generally agreed that the growth of the Neocortex , both absolutely and relative to the rest of the brain, during human evolution, has been responsible for the evolution of intelligence, however defined. In most mammals the neocortex has six layers, and its different functional areas (vision, hearing, etc) are sharply differentiated. The whale neocortex, on the other hand, has only five layers, and there is little differentiation of these layers according to function. This has led some to argue that the whale brain has not significantly evolved since the distant ancestors of the whale took to a marine lifestyle about 50 million years ago. From an evolutionary point of view, this is consistent with the principles of over the past million years. By contrast, the whale has faced no such environmental stimuli to brain evolution. Whales live in an unchanging and benign environment with few natural Predators . Their sole adaptation to their marine environment has been increasing size. The whale's lifestyle consists of swimming and eating, tasks which Fish perform perfectly competently with very small brains. From an evolutionary point of view, there is no reason for whales to have evolved intelligence, since their survival does not require them to perform any tasks for which intelligence is necessary. Whales have a sophisticated Social System . Their communication system may contain some of the elements of true Language , although our knowledge of whale communications is not very advanced. Many other animals, including Insects , have complex social systems, and many others, such as birds, have sophisticated communications. Whales also have very acute hearing, which gives them advanced echo-location capacities analogous to Sonar - but so do bats. All this has led many (though far from all) zoologists to the conclusion that there is no convincing evidence for whale intelligence. A better understanding of whale communications and Whale Behaviour may solve this problem eventually. WHALES AND HUMANS ''Main article Whaling '' Most species of large whales are endangered as a result of large-scale Whaling during the nineteenth and twentieth centuries. For centuries large whales have been hunted for oil, meat, baleen and Ambergris (a perfume ingredient from the intestine of Sperm Whale s). By the middle of the 20th century, whaling left many populations nearly or fully extinct. The International Whaling Commission introduced an open-ended moratorium on all commercial whaling in 1986. For various reasons some exceptions to this moratorium exist; current whaling nations are Norway , Iceland and Japan and the aboriginal communities of Siberia , Alaska and northern Canada . For details, see Whaling . Several species of small whales are caught as Bycatch in fisheries for other species. In the tuna fishery in the Eastern Tropical Pacific thousands of dolphins used to drown in purse-seine nets, until measures to prevent this were introduced. Fishing gear and deployment modifications, and eco-labelling (''dolphin-safe'' or ''dolphin-friendly'' brands of canned tuna), have contributed to an estimated 96% reduction in the mortality of dolphins by tuna fishing vessels in recent years. In many countries, small whales are still hunted for food, oil, meat or bait. Environmentalists have long argued that some cetaceans, including whales, are endangered by s occur in many species, mostly beaked whales that use echolocation systems for deep diving). The frequency and size of beachings around the world, recorded over the last 1,000 years in religious tracts and more recently in scientific surveys, has been used to estimate the changing population size of various whale species by assuming that the proportion of the total whale population beaching in any one year is constant. Despite the concerns raised about sonar which may invalidate this assumption, this population estimate technique is still popular today. Researchers in the area ( Talpalar & Grossman, 2005 ) support the view that it is the combination of the high pressure environment of deep-diving with the disturbing effect of the sonar which causes decompression sickness and stranding of whales. Thus, an exaggerated startle response occurring during deep diving may alter orientation cues and produce rapid ascent. Following public concern, the US Defense department has been ordered by the US judiciary to strictly limit use of its Low Frequency Active Sonar during peacetime. Attempts by the UK-based Whale And Dolphin Conservation Society to obtain a Public Inquiry into the possible dangers of the Royal Navy's equivalent (the "2087" sonar launched in December 2004) have so far failed. The European Parliament on the other hand has requested that EU members refrain from using the powerful sonar system until an environmental impact study has been carried out. {Link without Title} Conservationists are concerned that seismic testing used for oil and gas exploration may also damage the hearing and echolocation capabilities of whales. They also suggest that disturbances in magnetic fields caused by the testing may also be responsible for beaching. See e.g. ''Seismic testing and the impacts of high intensity sound on whales'', Lindy Weilgart, Department of Biology Dalhouise University (PDF format) WHALES IN CULTURE The Sea was described as "whale's road" in '' Beowulf ''. The 12:40). Nevertheless, the passages in question do not unambiguously refer to whales; modern translations tend to use other terms; for example the New International Version uses "creatures of the sea"; "monster of the deep"; "monster"; and "huge fish" respectively. The 's cross-examination of fundamentalist William Jennings Bryan in the 1925 Scopes Trial , as depicted in the drama " Inherit The Wind " by Jerome Lawrence and Robert E. Lee. The story of Jonas being swallowed by a whale is mentioned in the Qur'an as well. The Hunting Of Whales is the subject of one of the classics of the English Language literary canon, Herman Melville 's '' Moby-Dick .'' Melville classed whales as "a spouting fish with a horizontal tail", despite science suggesting otherwise the previous century. Melville acknowledged "the grounds upon which Linnaeus would fain have banished the whales from the waters" but says that when he presented them to "my friends Simeon Macey and Charley Coffin, of Nantucket ... they united in the opinion that the reasons set forth were altogether insufficient. Charley profanely hinted they were humbug." Melville's book is an extraordinary work, part adventure story, part Metaphysical allegory, and part Natural History ; it is essentially a complete summary of nineteenth-century knowledge about the biology, ecology and cultural significance of whales. Some cultures associate some level of divinity with the whale, such as in some places in Ghana and the Vietnamese , who occasionally hold funerals for beached whales, a throwback to Vietnam's ancient sea-based Austroasiatic culture. Festivals celebrating whales have sprung in both Sitka and Kodiak Alaska . They feature speakers on marine biology and celebrate the creatures with art, music, whale-watching cruises, and symposiums. SEE ALSO
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