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ADAPTATIONS OF SPECIES
reflect
Giraffes are unique animals because they have such long
necks. The neck of a modern day giraffe is much longer
than the neck of an ancient giraffe that lived long ago. How
and why did the giraffe change in such a way? What are
the advantages of having a long neck?
Natural Selection and Species Survival
Structures of living organisms demonstrate adaptations
that allow for specific functions. For example, the giraffe’s
long neck is an adaptation because it allows the giraffe
to reach leaves further up on trees. This provides an
advantage because the giraffe can reach food that other
adaptations: structures
animals cannot reach. Since a longer neck provides an
or behaviors in organisms
advantage, giraffes with this trait are more likely to survive,
that help them survive in
reproduce, and pass the trait to their offspring. This is
their environment
called natural selection. It is the process by which, over
generations, favorable traits become more common in a
species or population and unfavorable traits become less common.
Plants also have adaptations that help them survive. Water
lilies, for example, have large, thin leaves. The structure of
these leaves helps water lilies float so they can get enough
sunlight for photosynthesis. Because floating has an
advantage, plants that have this leaf structure can produce
more food during photosynthesis. The extra food helps the
plants make more seeds and pass on this trait to the next
generation.
Some plants, like tulips, store food in structures called bulbs. The bulbs grow underground.
During winter (or other harsh conditions like a drought), the above-ground structures of the
plant (stem, flower, leaves) die, but the bulb stays alive.
It produces a new stem, new leaves, and new flowers in
the spring. This adaptation helps the plant survive difficult
environmental conditions.
One challenge for animals that live in water is getting
enough oxygen. Animals that live on land use lungs to get
oxygen from the air. Fish have gills to help them take in
enough oxygen from the water. Fish gills can be difficult to
see because they are inside the animal.
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ADAPTATIONS OF SPECIES
Amphibians also have gills during the time that they live in water. These gills can be found
on the outside of the animal, as shown in the picture of the salamander on the previous
page. They look like feathery structures on each side of the body. Gills are adapted to have
many fringes to increase the area that can absorb oxygen from the water.
An internal adaptation in plants is the xylem. The xylem
is a structure that moves water through the plant. Plants
that do not have xylem, like the mosses shown in the
image on the right, are limited to wet climates. Xylem is
an adaptation that allows plants to grow in drier climates
because the xylem can draw water up from deep in the
soil.
what do you think?
If you examined a chicken or turkey bone, you would notice
that the bone is lightweight and hollow. In fact, most birds
have hollow bones. Why do you think this is so? What
adaptive advantage do hollow bones provide to a bird?
Behavioral Adaptations
The adaptations discussed so far have been structural,
or physical, adaptations. In the example above of hollow
bones in birds, the hollow structure of the bones allows
birds to fly. Therefore, birds can fulfill a role in the
environment that most other organisms cannot fill.
Animals also have behavioral adaptations. For example, humpback whales use unique
songs to communicate with one another. These songs can help a mother find her lost calf.
They can also be used to claim a territory and keep other whales at a distance. Or, the
songs can be used to find a mate. Whales that are better at communicating have many
advantages. A whale that is better able to attract a mate through song is more likely to
breed and pass that trait on to the next generation.
Squirrels and some other animals hibernate to help
them get through times of the year during which
temperatures are cold and food is limited. Animals that
hibernate do not eat and rely on stored body fat for
energy. Thus, the timing of hibernation is important.
An animal that hibernates too long may run out of fat
reserves. An animal that awakes from hibernation too
hibernate: a process during
which an organism undergoes
a slowed physiological state
to survive long periods of cold
temperature or reduced food
supplies
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ADAPTATIONS OF SPECIES
soon may not find food. Producing enough fat reserves is also an essential component of
this adaptation. Animals that have more fat reserves when they enter hibernation are more
likely to survive the winter.
Monarch butterflies and many species of birds have a different
behavioral adaptation for surviving cold winters. They leave the
area. These animals migrate from
migrate: to move to a
northern areas in the summer to
different geographical
southern areas in the winter.
or climatic region where
food is more available
look out!
Natural selection does not have a goal. Organisms cannot plan to have “better” offspring.
Organisms that are born with more favorable traits are more likely to survive and reproduce
than organisms born with less favorable traits. Those organisms that survive and reproduce
pass their traits on to the next generation. What makes a trait more or less favorable? Many
times it depends on the environment. A trait that is favorable for living in the arctic may not
be favorable for living in the desert.
Genetic Variation
Natural selection is possible because of genetic
variation among organisms within a population.
In a population of giraffes, for example, individuals
vary in height (as well as other traits.) Some of these
individuals have more favorable sets of traits; others
have less favorable sets of traits. The individuals
with the most favorable set of traits will survive and
reproduce to pass on those traits. It is the variation
between individuals that allows for natural selection.
population: members of the
same species that live in the
same geographical area; may
be distinctly different than
populations living elsewhere,
due to the spread of local
adaptations within a population
The process of natural selection has changed nearly every species found on Earth.
For example, the Galapagos Medium Ground Finch has developed a unique beak
shape allowing it to fill a specific role in its environment and improve its ability to
survive. The ground finches of the Galapagos (a group of islands in the Pacific Ocean)
feed mainly on seed. Several different species of finches evolved from a common
ancestor that was a seed-eating ground finch with a relatively small, pointy beak. Each
species specializes in feeding based on beak size. For example, the large ground finch
(Geospiza magnirostris) has a large beak and feeds mainly on large seeds. The small
ground finch (Geospiza fuliginosa) has a small beak and feeds mainly on small seeds.
The medium ground finch (Geospiza fortis) as a medium-sized beak. This allows the
bird to be more of a generalist; it is able to eat either large or small seeds. The mediumsized beak provides an advantage because it has increased options for feeding, so its
chances of survival are greater.
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ADAPTATIONS OF SPECIES
Populations and species demonstrate unique
variations and inherited traits, which have gradually
changed over time as they were passed from
one generation to the next. Changes in external
features, internal features, and behaviors of
organisms, through natural selection can enhance
the survival of a species or produce desired genetic
traits.
Scientists in the Spotlight: Peter and Rosemary
Grant
Peter and Rosemary Grant are biologists who
studied the Galapagos finches. They were able to
observe natural selection over the course of a few
generations of the finches when the environment
dramatically changed. For example, in 1977 a drought resulted in more large seeds and
fewer small seeds. The average beak size of medium ground finches was larger after the
drought than before the drought. After a particularly wet year in 1985, the average finch
beak was smaller. Smaller seeds were more plentiful and the smaller-beaked finches were
more successful at survival and reproduction that year.
This data is important because it helps scientists measure and describe natural selection.
Obtaining the data took years of careful measuring and weighing. Peter and Rosemary
Grant spent a few months each year on the Galapagos Islands. They measured the finches
and collected weather data for many years. This dedication resulted in a long-term study
that showed natural selection in action.
Everyday Life: Selective Breeding
In selective breeding, the favorable traits to be passed
on to offspring are chosen by a breeder. Selective
breeding of domestic animals, like dogs, has led to
incredible diversity from their wolf ancestor. Dogs are as
diverse as the Great Dane and Chihuahua; yet they had
a common ancestor. People
who selectively breed animals
domestic: related to
select for particular traits and
the household
breed only the animals that
have those traits. After many
generations, each breed has highly specific traits that
have been selected for. Some breeds are the result of
breeding for a good sense of smell, a good protective
instinct, unique fur patterns, or a particular body shape.
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ADAPTATIONS OF SPECIES
People also selectively breed plants. Wild corn, for
example, has very small kernels. Over many years
of breeding, humans have created modern corn with
the large kernels like we expect to see in the grocery
store. People prefer to purchase the larger kernels.
Therefore, farmers plant the seeds that produce the
desired traits. Other crops, like wheat, have also been
selectively bred to produce desirable traits. Modern
wheat crops are more resistant to harsh weather
and produce more wheat per growing season. Some
modern crops are even bred to contain more vitamins!
What do you know?
The chart on the next page lists examples of
adaptations in different organisms. For each example, state whether the adaptation is likely
the result of natural selection or selective breeding. Then, describe at least one advantage
for the adaptation. Be accurate, but creative! Many items in the chart have more than one
answer.
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ADAPTATIONS OF SPECIES
Example of Adaptation
Apples with large, sweet fruit
Natural Selection or
Selective Breeding?
Advantage(s) of
Adaptation
Cacti with sharp spines
Bats that can fly
Crabs that can hide in the sand
Tomato plants that can grow in
salty environments
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ADAPTATIONS OF SPECIES
connecting with your child
Artificial Selection at the Grocery Store
To help your child learn more about
adaptations, investigate selective breeding
(also called artificial selection) by taking a
trip to the grocery store or farmer’s market.
If you are unable to travel to the market
together, try to find samples of fruits and
vegetables in your refrigerator or search for
pictures on the Internet.
Selective breeding is common in food crops;
these crops are often called genetically
modified crops. Breeders can select for
a variety of traits, such as leaf size in
lettuce, fruit size in tomatoes, root size and
vitamin content in carrots, and flower size
in cauliflower. Choose at least six different
fruits and/or vegetables to discuss. Most
of the traits selected for by breeders can
be beneficial in the wild within the limits
of a particular range of variability. For
example, larger leaves help a plant by
increasing photosynthesis, but they can also
increase the potential for frost or herbivore
damage. Larger fruit can be advantageous
by attracting dispersing animals, but it
also requires a lot of energy from the fruitproducing plant. Some traits, however, are
entirely of benefit to humans and not the
plant. Seedless plants, for example, would
not be selected for by natural selection.
Here are some questions to discuss with the
student:
• Which traits do you think were artificially
selected for in each fruit or vegetable?
Why do you think these traits were
selected?
• Would similar adaptations be beneficial
or harmful in the wild?
• Which type of environmental conditions
would be most favorable for these
plants?
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