Charles Darwin developed the theory of evolution by natural selection after observing species diversity during his voyage on the HMS Beagle. He noticed that species on the Galapagos Islands had adapted to their environments in ways that increased their chances of survival, such as through variations in beak shape among finches. Darwin's theory explained how species evolve over generations through natural selection of inheritable traits best suited for an organism's environment.

1. Evolution
Charles Darwin and
The Origin of Species

2. Charles Darwin (1809-1882)
► He was an English Naturalist
► He traveled around the world on his
ship, the Beagle
► Studied species and fossils in the
Galapagos Islands and around the
world
► Why did some species survive while
others became extinct?
► Natural selection
► Published The Origin of Species in
1859

3. Darwin’s Theory
► Darwin's theory of evolution has four main parts:
Organisms have changed over time, and the ones living
today are different from those that lived in the past.
Furthermore, many organisms that once lived are now
extinct. The world is not constant, but changing.
All organisms come from common ancestors by a process of
branching. Over time, populations split into different species,
which are related because they are descended from a common
ancestor. Thus, if one goes far enough back in time, any pair of
organisms has a common ancestor. This explained the
similarities of organisms that were classified together -- they
were similar because of shared traits inherited from their
common ancestor. It also explained why similar species tended
to occur in the same geographic region.
Change is gradual and slow, taking place over a long time.
This was supported by the fossil record, and was consistent
with the fact that no naturalist had observed the sudden
appearance of a new species.
The mechanism of evolutionary change is natural selection.

4. Natural Selection
► “I have called this principle, by which each slight
variation, if useful, is preserved, by the term of
natural selection.”
– Charles Darwin - The Origin of Species
► Darwin's theory of natural selection holds that
variation within species occurs randomly and that
the survival or extinction of each organism is
determined by that organism's ability to adapt to
its environment.

5. On The Galapagos Islands
► Darwin found mockingbirds that were similar to ones that were native
to Chile, but differed slightly from island to island
► He studied different species of finches and the slight variations in
their beaks
► He noticed that the shapes of tortoise shells also varied slightly from
island to island
► He found fossils of animals that had recently become extinct
► He kept a journal and collected fossils and specimens for further
study

6. Darwin’s Finches
► These are some of the finches that Darwin
studied on his voyage
► Though they are all finches, their beaks
distinguish them from one another
► Some finches developed short, strong beaks
that made it possible for them to crack nuts
► Some developed long, fine beaks to reach
insect larvae in tiny holes
► This is an example of how these finches
adapted to their environment to survive
(natural selection)

7. Darwin’s Finches
Darwin believed that all of the different finches came from a common ancestor
and that their differences were a result of natural selection

8. Example of Natural Selection
Peppered Moth
 Moths can camouflage with trees to avoid
being eaten by birds.
► There were light moths and dark moths living
near English industrial cities in the 19th century
 The dark moths stood out on the light
colored trees and were more likely to be
seen and eaten by birds
► Thus, there were many more light
colored moths than dark colored moths.
► As English factories produced more and more
soot, the trees turned a darker color. This was
able to camouflage the dark moths, but not the
light moths
 THEN, the light moths stood out on the dark
trees and were more likely to be seen and
eaten by birds!
► Thus, there were more dark colored
moths than light colored moths.
Because the dark moth was able to
camouflage it was able to avoid
being eaten.
If the light colored moth is not
able to adapt to its environment
then it will eventually become
extinct.

9. Camouflage
► Many animals have evolved to resemble the environment around them.
► This makes it very difficult for predators to find them and eat them, thus increasing their
chance of survival. It also makes it easier for predators to sneak up on prey.
► Can you spot them?
Brimstone Butterfly Stick Bug Large Fly Preying Mantis
Camo Moth
Seal
Lion

10. Patterns of Evolution
► Darwin believed that natural selection
can ultimately lead to the formation of
new species.
► Sometimes many species evolve from a
single ancestral species.
► Similarities in skeletal and muscular
structure of Hawaiian honeycreepers led
scientists to conclude that the 23 species
of honeycreepers evolved from one
ancestral species.
► Such an evolutionary pattern, in which
many related species evolved from a
single ancestral species, is called
adaptive radiation.

11. Adaptive Radiation
► Adaptive radiation most commonly occurs
when a species of organisms successfully
invades an isolated region where few
competing species exist. If new habitats
are available, new species will evolve.

12. Divergent Evolution
► Divergent evolution is the process of two or
more related species becoming more and
more dissimilar.
► Example: The red fox and the kit fox
 The red fox lives in mixed farmlands and
forests, where its red color helps it blend in
with surrounding trees.
 The kit fox lives on the plains and in the
deserts, where its sandy color helps conceal it
from prey and predators. The ears of the kit
fox are larger than those of the red fox. The
kit fox's large ears are an adaptation to its
desert environment
► Similarities in structure indicate that the red
fox and the kit fox had a common ancestor.
As they adapted to different environments,
the appearance of the two species diverged,
or became more and more different.
Red Fox
Kit Fox

13. Convergent Evolution
► Convergent evolution is the opposite of divergent
evolution
► In convergent evolution, unrelated species become
more and more similar in appearance as they adapt to
the same kind of environment.
► Frogs and Chameleons are examples of convergent
evolution because although they are different
amphibians, they have both developed harpoon-like
tongues to catch insects

14. Co-evolution
► Co-evolution is the joint change of two or more
species in close interaction. Predators and their prey
sometimes co-evolve; parasites and their hosts often
co-evolve; plant-eating animals and the plants upon
which they feed also co-evolve.
► One example of co-evolution is pollination of orchids
by African moths.
 These species co-evolve because the moths depend on
the flowers for nectar, and the flowers depend on the
moths to spread their pollen so that they can
reproduce.
► The relationship between the moth and the orchids is
mutually beneficial because they help each other
survive.

15. Why is This Important?
Divergent, convergent and co-evolution are
different ways organisms adapt to the
environment. These are examples of how the
diversity of life on earth is due to the ever-
changing interaction between a species and
its environment.

16. Extinction
► Extinction is the disappearance of an entire species
► If a species does not have the genetic traits to survive in its
environment, then the species will eventually become extinct
forever
► Some examples of extinct animals are:
Thylacine Quagga Dodo Bird
Galapagos Tortoise
Bali Tiger
Dinosaurs Steller’s Sea Cow Laughing Owl

17. Reasons for Extinction
 Rarity- when there are very few animals of a species left
(Galapagos Tortoise)
 Inbreeding- when animals mate too much within their own
group the offspring become less able to survive and adapt in a
healthy way
 Hybridization-When two animals from different sub-species
mate, they might pass on genes that are less healthy (Quagga-
half horse half zebra)
 Gradual loss of habitat- When an animal's habitat is slowly
destroyed and they have nowhere to live. (Bali Tiger)
 Long-term environmental trends- Scientists think that dinosaurs
became extinct because of a slow cooling of the earth

18.  Catastrophe- Volcanic eruption, dramatic change in climate, tsunami,
etc.
 Extinction or reduction of mutualistic population- If two species are
dependent on each other, then the endangering of one also endangers
the other
 Competition- When a new species is introduced to a habitat, then the
stronger of the two species will be more likely to survive.
 Predators-When the population of a species of predator in a habitat
suddenly increases, the population of their prey decreases
 Disease- If a particular sickness spreads quickly throughout a
particular species, then many may die before they can reproduce
 Hunting and collecting- Hunters have been largely responsible for the
endangerment of many animal species.
Reasons for Extinction

19. Applications
 Knowledge about evolution and natural selection
has benefited our society in many ways, and has
helped make numerous technological advances,
especially in the field of biology and medicine
 Using Darwin’s theory of natural selection, scientists
have been able to identify the desirable traits which
would improve the probability of survival in certain
species
 It has helped scientists and doctors in treating viruses
and diseases.

20.  Did you know that when a doctor gives you antibiotics, you need to
continue taking them until all of the pills are gone, even if you start
to feel better? When a doctor gives you antibiotics, they start to fight
of the bacteria in your body, little by little. It starts with the weak
bacteria, and eventually kills the strongest bacteria.
 BUT, if you stop taking your medicine, then it is only the STRONG
bacteria that are left in your body. That means that they will
continue to reproduce and become stronger and stronger, and it will
be much harder for the medicine to kill them. This is an example of
natural selection because the strong bacteria survives and grows.
FOR EXAMPLE

21. Conclusion
► Darwin’s observations have
made a great impact in the
scientific community.
Because of his observations,
we are better able to
understand why some species
survive and some die.
► We are also better able to
take precautions to protect
species that are endangered.
► Lastly, we can understand the
diversity in the world around
us and learn to appreciate it.