Whales are the largest species of exclusively aquatic mammals,
members of the order Cetacea, which also includes dolphins and porpoises.
They include the largest known animals to have 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 porpoises.
This can lead to some confusion because Orcas ("Killer Whales")
and Pilot Whales have "whale" in their name, but they
are dolphins for the purpose of classification.
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
whales and baleen whales) 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 whales have two; toothed
whales 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.
Their skin has evolved hydrophilic properties. Its surface is covered
with microscopic pores surrounded by nanoridges. Between these ridges
there is a rubber-like gel which is excreted from the gaps between
the skin cells. This gel contains enzymes that attacks microbes,
and the edge of the ridges makes it hard for smaller organisms to
Whale flukes often can be used as identifying markings, as is the
case for humpback whales. This is the method by which the publicized
errant Humphrey the whale was identified in three separate sightings.
Whales are broadly classed as predators, 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
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.
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
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 dolphins or chimpanzees, for instance, it is extremely
difficult to test these views experimentally.
Some whale species 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
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