Transcript Evolution

Charles Darwin and
The Origin of Species
What do you think of when you hear the word
Evolution is a very complex and controversial issue. This lesson is an
introduction to the theory of evolution and natural selection as Humans?
by Charles Darwin
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
► Why did some species survive while
others became extinct?
► Natural selection
► Published The Origin of Species in
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.
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.
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.
The mechanism of evolutionary change is natural selection.
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.
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
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
Darwin’s Finches
These are some of the finches
that Darwin studied on his
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
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
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
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
Camo Moth
Stick Bug
Large Fly
Preying Mantis
Patterns of Evolution
Darwin believed that natural selection can
ultimately lead to the formation of new
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
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.
Divergent Evolution
Red Fox
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
Kit Fox
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.
Convergent Evolution
Convergent evolution is the opposite of divergent
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
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
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.
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:
Galapagos Tortoise
Bali Tiger
Steller’s Sea Cow
Laughing Owl
Dodo Bird
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
Reasons for Extinction
Catastrophe- Volcanic eruption, dramatic change in climate, tsunami,
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.
► 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
 It has helped scientists and doctors in treating viruses
and diseases.
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.
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.