The Galapagos Islands provided evidence for Darwin's theory of evolution by natural selection through the adaptive radiation of finches. A single finch species migrated to the islands and diverged into 13 species as they adapted to different ecological niches and food sources. The beak shapes of the finch species evolved to suit their specific diets, such as seeds, insects, or blood, demonstrating how natural selection can drive speciation.

7. The process in which one species gives rise to multiple
species that exploits different niches.

9. The process in which one species gives rise to multiple
species that exploits different niches.
The ecological niches exert the selection pressures that push
the populations in various directions.
Selective Pressures:
Environmental forces such as scarcity of food or extreme temperatures
that result in the survival of only certain organisms with characteristics
that fits the change.

12.  Evolution of New Physical Traits

13.  Availability of New Niches

14.  Aftermath of Mass Extinctions

15. The amount of melanin in our skin. Shows our adaptations in living in areas
of different climates. Dark skinned people will be found in hotter climates.
While light skinned people are found in areas with cold climates.

16. Homology
traits inherited by two different
organisms from a common
ancestor
Analogy
traits serve similar functions but
are not evolutionary related
Convergent Evolution
The same biological
traits in unrelated
lineages
Divergent Evolution
The same species
adapting to different
environment

17. Tetrapods
animals with
four legs.
Notice how these tetrapod limbs are similar to one another:
•They are all built from many individual bones.
•They are all spin-offs of the same basic bone layout:
one long bone (the humerus) attached to two other long bones (the
radius and ulna), with a branching series of smaller bones (carpals,
metacarpals and phalanges) on the end.

18. Here you can see the same bones labeled in these different limbs:
Even though these limbs are similar to one another, the animals they
belong to are quite different from one another.
What animals possess these homologous limbs?

19. Homology
traits inherited by different
organisms from a common
ancestor
Divergent Evolution
The same species adapting to different
environment
The result of:

20. Divergent Evolution
The same species adapting to
different environment
Homology
traits inherited by two different
organisms from a common
ancestor

21. Homology
traits inherited by two different
organisms from a common
ancestor
Analogy
traits serve similar functions but
are not evolutionary related
Convergent Evolution
The same biological
traits in unrelated
lineages
Divergent Evolution
The same species
adapting to different
environment

22. Sharks Dolphins
You have probably noticed that dolphins and sharks both have a streamlined body
shape with a triangular fin on the back and two side fins. However, the two animals
also have many differences.
skeleton made of cartilage
use gills to get oxygen from the water in
which they swim
don't nurse their young
don't have hair
skeleton made of bone
go to the surface and breathe atmospheric
air in through their blowholes
do nurse their young
do have hair —around their "noses"

23. The following tree shows the relationship between various groups, including
cartilaginous fishes (sharks) and mammals (dolphins).
They are not very closely related to one another.
So how did they end up looking so much alike?

24. •If two species face a similar problem, challenge or opportunity, evolution may
end up shaping them both in similar ways.
•Both dolphins and sharks swim after prey in the ocean. Streamlined bodies and
fins provide a big advantage for them, allowing them to swim faster.
•We know that dolphins and sharks are not closely related, and they didn't inherit
their similar body shapes from a common ancestor.
•Their streamlined bodies, dorsal fins and flippers are the result of convergent
evolution.
•Since dolphins and sharks occupy similar niches and face similar challenges,
similar adaptations have been advantageous to them, resulting in their analogous
structures.

25. Test your understanding
You learned that homologies are traits that
different lineages inherited from their common
ancestor.
Homologies are evidence that different species
shared a common ancestor.
Analogies, on the other hand, are similar traits
that were not inherited from a common
ancestor but that evolved separately.
Analogies often exist because two different
lineages became adapted for similar lifestyles.
Sugar gliders and flying squirrels look amazingly
similar.
They are both furry animals of about the same
size, with big eyes and a white belly. And they
both glide from treetops using a thin piece of
skin that is stretched between their legs.
This piece of skin helps keep them stable while
gliding.
Flying squirrel
Sugar glider

26. Test your understanding
Flying squirrel
Sugar glider
However, these animals also have some key
differences:
•Sugar gliders live in Australia, and flying
squirrels live in North America.
Sugar gliders have a pouch (like a kangaroo
does), which provides shelter and safety for
their tiny babies — at birth, a baby sugar
glider is smaller than a peanut!
•Flying squirrels, on the other hand, have
much larger babies and no pouch.
By studying their genes and other traits,
biologists have figured out that sugar gliders
and flying squirrels are probably not very
closely related.
Sugar gliders are marsupial mammals and
flying squirrels are placental mammals.

27. Considering all of the evidence, are the "wings"
(actually flaps of skin stretched between the legs)
of sugar gliders and flying squirrels homologous or
analogous structures?
Homologous Analogous

28. The "wings" of sugar gliders
and flying squirrels are
analogous, not homologous.
Homologies are traits inherited
from a common ancestor, and
analogies are similar traits that
evolved independently of one
another.

29. Since sugar gliders and flying squirrels are very distantly related, it seems very unlikely that their
common ancestor had flaps of skin stretched between its legs and that both modern animals
inherited the trait from this animal.
Since sugar gliders and flying squirrels are very distantly related, it seems very unlikely that their
common ancestor had flaps of skin stretched between its legs and that both modern animals
inherited the trait from this animal.
Instead, each lineage probably evolved the trait independently as adaptations for gliding and
tree-living.

30. AnalogyHomology

40. In biology, the independent evolution of
similar structures in species (or other
taxonomic groups) that are not closely related,
as a result of living in a similar way. Thus, birds
and bees have wings, not because they are
descended from a common winged ancestor,
but because their respective ancestors
independently evolved flight.
In such cases, the structures often differ in
their anatomical origins and are only
superficially similar. Such structures are said to
be ‘analogous’, in contrast to the homologous
organs of related groups.

46. a
When Charles Darwin stepped ashore on the Galapagos Islands in September 1835, it was the start of five weeks that
would change the world of science, although he did not know it at the time. Among other finds, he observed and
collected the variety of small birds that inhabited the islands, but he did not realize their significance, and failed to
keep good records of his specimens and where they were collected. It was not until he was back in London, puzzling
over the birds, that the realization that they were all different, but closely related, species of finch led him toward
formulating the principle of natural selection.
In his memoir, The Voyage of the Beagle, Darwin noted, almost as if in awe, "One might really fancy that, from an
original paucity of birds in this archipelago, one species had been taken and modified for different ends."
Indeed, the Galapagos have been called a living laboratory where speciation can be seen at work. A few million years
ago, one species of finch migrated to the rocky Galapagos from the mainland of Central or South America. From this
one migrant species would come many -- at least 13 species of finch evolving from the single ancestor.
This process in which one species gives rise to multiple species that exploit different niches is called adaptive
radiation. The ecological niches exert the selection pressures that push the populations in various directions. On
various islands, finch species have become adapted for different diets: seeds, insects, flowers, the blood of seabirds,
and leaves.
The ancestral finch was a ground-dwelling, seed-eating finch. After the burst of speciation in the Galapagos, a total of
14 species would exist: three species of ground-dwelling seed-eaters; three others living on cactuses and eating
seeds; one living in trees and eating seeds; and 7 species of tree-dwelling insect-eaters.
Scientists long after Darwin spent years trying to understand the process that had created so many types of finches
that differed mainly in the size and shape of their beaks.
Most recently, Peter and Rosemary Grant have spent many years in the Galapagos, seeing changing climatic
conditions from year to year dramatically altering the food supply. As a result, certain of the finches have lived or
died depending on which species' beak structure was best adapted for the most abundant food -- just as Darwin
would have predicted.