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Giraffes are one example of an animal that
looks very distinct because it has adapted to survive in its
environment. A giraffe's long neck helps it to eat leaves
from high up in trees, where it doesn't have to compete with
many other animals for food.
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Living organisms are adapted to their environment. This means that the
way they look, the way they behave, how they are built, or their way of
life makes them suited to survive and reproduce in their habitats. For
example, giraffes have very long necks so that they can eat tall vegetation,
which other animals cannot reach. The eyes of cats are like slits. That
makes it possible for the cat's eyes to adjust to both bright light, when
the slits are narrow, and to very dim light, when the slits are wide open.
Behavior is also an important adaptation. Animals inherit many kinds
of adaptive behavior. In southern Africa there are small animals called
meerkats, which live in large colonies. The meerkats take turns standing
on their hind legs, looking up at the sky to spot birds of prey. Meanwhile,
the meerkats in the rest of the colony go about their lives. You can probably
think of many other features of body or behavior that help animals to
lead a successful life.
In biology, an ecological niche refers to the overall role of a species
in its environment. Most environments have many niches. If a niche is
"empty" (no organisms are occupying it), new species are likely
to evolve to occupy it. This happens by the process of natural selection.
By natural selection, the nature of the species gradually changes to become
adapted to the niche. If a species becomes very well adapted to its environment,
and if the environment does not change, species can exist for a very long
time before they become extinct.
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Copyright © Washington State
University, College of Veterinary Medicine
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Photograph of a "dew" claw of a dog. At one point,
the modern dog's ancesteors probably needed this toe, but
it is not used by the modern dog.
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An excellent example of an animal evolving to fill a niche is seen in
the evolution of horses. Many fossils of different kinds of horses have
been discovered, and paleontologists think that the earliest ancestor
of the modern horse lived in North America more than 50 million years
ago. This animal was a small padded-foot forest animal about the size
of a dog. If you saw one next to a modern horse, you might not even think
the two were related! As time passed, the climate of North America became
drier, and the vast forests started to shrink. Grasses were evolving,
and the amount grassland was increasing. Horses adapted to fill this new
grassland niche. They grew taller, and their legs and feet became better
adapted to sprinting in the open grasslands. Their eyes also adapted to
be further back on their heads to help them to see more of the area around
them. Each of these adaptations helped the evolving grassland horses to
avoid predators. Their teeth also changed to be better adapted to grinding
tough grassland vegetation.
Have you ever wondered what purpose the "dew" claw on the inside
of a dog's paw serves? The claw is the dog's thumb. Because a dog runs
on the balls of its feet and four digits, the claw no longer serves a
purpose. Organs or parts of the body that no longer serve a function are
called vestigial structures. They provide evidence that the species is
still changing. Even humans have vestigial structures. The human appendix
is one such example. It used to store microbes that helped to digest plant
matter, but it is no longer needed in the human.
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