Transcript EVOLUTION EVOLUTION Evolution means a gradual change over time. Since its formation about 4,5 billion years ago, the earth itself has changed continuously.

EVOLUTION
EVOLUTION
Evolution means a gradual change over time.
Since its formation about 4,5 billion years
ago, the earth itself has changed
continuously. This slow change is known as
geological evolution.
Many species also have changed since they
first appeared. This process is known as
organic evolution.
The theory of evolution
assumes that the
organisms living today are
formed from some
preexisting organisms that
have changed over time. It
also assumes that the
change is a continuous
process and the
organisms that can adapt
to the changing
environmetal conditions
will survive, where the
ones that can not won’t.
The basic idea of Theory
of Evolution is that all
species have a common
ancestor.
EVIDENCE of EVOLUTION
1.
2.
3.
4.
5.
6.
Paleontological (fossil) Evidence
Evidence from classification
Morphological Evidence
Evidence from Vestigial structures
Embryological Evidence
Comparative Biochemical and Physiological
Evidence
7. Evidence from domestication
8. Evidence from Cytology
9. Evidence from Geographical Distribution
1. Paleontological (fossil) Evidence
• The study of fossils provides the strongest
evidence of organic evolution.
• A fossil is any trace or remains of an organism
that has been preserved by natural processes.
• Special circumstances are required for a fossil to
form.
• In the majority of fossils, the soft tissues of the
organism decayed, and only the hard parts, such
as bones or shells, have been preserved.
• In some fossils, however, an entire organisms
has been with almost no decay
Progressive series of fossils
leading from an ancient,
primitive organism to a
modern form.
Even though the fossil
record is not complete (and
is likely to never be
complete) we can form a
picture from the fossils we
do have. Some animals are
better respresented than
others - like the horse
2. Evidence from classification
• All organisms are arranged in taxonomic
categories in modern biology and the
similarities between different species are
used to estimate the hereditary
relationship between them.
• Species sharing many of the same
characteristics are believed to share a
common ancestor.
3. Morphological Evidence
• The presence of certain types of
similarities offers evidence for the
evolutionary relationships between
species.
• If living organisms are descended from a
common ancestor, then closely related
species should have more similar
structures than distantly related species.
3. Morphological Evidence
• Parts of different organisms that have similar
structures and similar embryonic
development, but have different forms and
functions are called homologous structures.
• Ex: human hand
adapted for grasping
whale’s flipper
adapted for swimming
wings of bats
adapted for flying
forearm of the horse
adapted for walking
They all have different functions
but they are internally very similar
Homologous
structures
The forearms of a cat, bat, whale and human are used for entirely different
things (walking, flying, swimming, grasping) and yet they are composed
of the exact same bones, just arranged differently and with slight
alterations
4. Evidence from Vestigial structures
• Vestigial structures are remnants of
structures that were in an ancestral form of
an organism.
• In modern organisms, vestigial structures are
reduced in size and serve little or no function.
• In the human body there are more than 100
vestigial structures, including the coccyx
(tailbone), the appendix, the wisdom teeth
and the muscles that move the nose and
ears.
4. Evidence from Vestigial structures
• Ex: Both whales and phytons have
vestigial hind leg bones embedded in the
body wall.
Apparently,
whales and
snakes evolved
from four legged
ancestors.
Vestigial
structures
5. Embryological Evidence
Embryos of closely related
species show similar patterns
of development.
In vertebrate embryos, there
are many similarities during
the early stages of
development.
For ex; all of the embryos
have gill slits, two chambered
hearts and tails. These
similarities support the idea
that these organisms have a
common ancestor.
5. Embryological Evidence
6. Comparative Biochemical and
Physiological Evidence
• The more closely related the species are
to one another, the greater the
biochemical similarities. Because all DNA
is descended from the DNA carried by the
earliest life forms, the DNA of all
organisms shares a common genetic
code. These similar genes direct the
synthesis of similar proteins in different
organisms.
6. Comparative Biochemical and
Physiological Evidence
• For ex; cytochrome c, a protein molecule
that every organism needs for cellular
respiration differs between species.
Differences in amino acids from humans in vertebrate hemoglobin polypeptides
6. Evidence from domestication
• For thousands of years
humans have selected
several species of animals
and plants to domesticate.
As a result, variations within
the species occurred.
• Today great variety of
animals and plants are
present which are produced
by the hybridization methods.
These organisms can mate
with each other and produce
fertile offspring and this
indicates that these
organisms are descended
from a common ancestor.
6. Evidence from domestication
7. Evidence from Cytology
• Plants and animals are composed of cells
that are similar in structure. This might
prove that these organisms come from a
common ancestor.
Endosymbiotic Theory
• Chloroplasts and mitochondria
are about the same size as
bacteria (prokaryotes).
• Both have a double membrane,
a remnant of endosymbiotic
event.
• Both have circular DNA, genetic
similarities to bacteria.
• Both have their own ribosomes,
protein synthesis machinery.
• Similar biochemical
organization.
8. Evidence from Geographical
Distribution
• The study of the past and present
geographical distribution of organisms is
called biogeography. It is concerned on
how geological and climate changes can
influence the distribution of species.
• One of the basic idea of biogeography is
that each species originated only once.
EARLY THEORIES OF
EVOLUTION
Lamarck’s Theory of Evolution
According to Lamarck’s theory, evolution involved in
two principles;
1.
The Law of Use and Disuse:
The more an animal uses a
particular part of its body, the
stronger and better
developed that part becomes.
At the same time, the less a
part is used, the weaker and
less developed it becomes.
Ex: An athlete develops the
strength of certain muscles by
constant use.
Lamarck’s Theory of Evolution
2. The Inheritance of Acquired Characteristics
Lamarck assumed that the characteristics of an
organism developed through use and disuse could
be passed on to its offspring.
Ex: Ancestors of modern giraffes had short necks and
fed on grasses. As the supply of food near the
ground decreased, the giraffes had to stretch their
necks to reach leaves of the trees.
Their necks become longer from
strecthing and this trait was passed
on to their offsprings.
Weissman’s Experiment
• Lamark’s second theory is incorrect as modern
genetics has shown that the traits pass from one
generation to the next but these genes are not
affected by an individuals life experiences or
activities.
• The most well known experiment that tries to
support Lamarck’s theory but failed, was
performed by Weismann.
• Weismann cut the tails off mice for 22
generations. In each generation, the mice were
born with tails of normal length.
Modification
All organisms have some changes due to
the environmental conditions. These
changes which are not hereditary are
called modification. Lamarck’s second
theory is actually about modification.
Ex: Our skin gets darker in the sun
Darwin’s Theory of Evolution
Darwin’s Observations
Darwin made several types of observations during his trips to the
South America coastlines and some islands.
Darwin’s Theory of Evolution
The most significant of Darwin’s observations were those he made on the
Galapagos Islands. He found many different species of finches living on
these islands. The birds were alike, yet each species was slightly different
from those on the next island or in another part of the same island.
Darwin’s Theory of Evolution
Darwin made similar observations
about many plants, insects and other
organisms. While species on the
Galapagos Islands resembled species
on the mainland, they were always
different in certain charactersitics.
Darwin came to believe that these
organisms originally had reached the
islands from the mainland. Because of
their isolation on the islands, the
species had opportunities to develop
special adaptations to each different
region.
Darwin’s Theory of Evolution
The six main points of Darwin’s theory are;
1. Overproduction: Most species produce far more
offspring than are needed to maintain the population.
Species populations remain more or less constant
because only small fraction of offspring live long
enough to reproduce.
2. Competition: Since living space and food are limited,
offspring in each generation must compete among
themselves and with other species.
Only a small fraction can possibly survive long enough
to reproduce.
Darwin’s Theory of Evolution
3.
Variation: The
characteristics of the
individuals in any species
are not exactly alike. They
may differ in exact size or
shape of a body, and so
on. These differences are
called variations.
Some variations may not
be important. Others may
affect the individual’s
ability to get food, to
escape enemies or to find
mate. These are vital
importance.
Darwin’s Theory of Evolution
4. Adaptations: Because of
variations, some individuals will
be better adapted to survive and
reproduce than others. In the
competition for existence, the
individuals that have favorable
adaptations to their environment
will have a greater chance of
living long enough to reproduce.
An adaptation is any kind of
inherited trait that improves an
organism’s chances of survival
and reproduction in a given
environment.
Adaptations
Structural Adaptations involve the body
of an organism.
Ex: The wings of birds or insects are
structural adaptations for flight.
The fins of fish and the webbed feet of
ducks are structural adaptations for
swimming.
Physiological adaptations involve the
metabolism of organisms.
Ex: Protein web made by spiders and the
poison venom made by snakes
Adaptations
Camouflage: The
organism blends into the
environment.
Warning coloration: The
colors of the animal make
it unpleasant it to eat and
protects it from predators.
Mimicry: The organism is
protected from its enemies
by its resemblance to
another species.
Adaptations
In Mullerian mimicry, the model is not defined and several unpalatable
species share warning colors or patterns to evade predation. Both
models and mimics are toxic. Several species from several different
orders may comprise a mimicry complex. The advantage is that the
predators need only encounter one form to shun the entire complex.
Adaptations
Batesian mimicry involves a palatable, unprotected species (the mimic)
that closely resembles an unpalatable or protected species (the model).
One example is this fly which looks like a bee. Birds know not to attack
a bee as they will be stung.
Darwin’s Theory of Evolution
5. Natural Selection:
In effect, the environment
selects plants and animals
with optimal traits to be the
parents of next
generations. Individuals
with variations that make
them better adapted to
their environment survive
and reproduce in greater
numbers than those
without such adaptations.
Darwin’s Theory of Evolution
5. Natural Selection:
Industrial melanism is the term used for the development
of dark-colored organisms in a population exposed to
industrial air pollution and it is an example of observed
natural selection.
Darwin’s Theory of Evolution
Before England became
industrialized, the light –
colored moths blended in well
with the lichens that covered
the bark of the tree. As a
result of this camouflage,
birds that feed on the
peppered moth could not
easily find them. Dark –
colored moths were easily
eaten by the birds.
When the air pollution killed
the lichens and blackened the
trees, light-colored moths
became easy prey for birds.
Darwin’s Theory of Evolution
Bacterial resistance to antibiotics
Antibiotics usually kill bacteria. However, once the use of antibiotics became
common, resistant strains of bacteria began to appear.
In a large population of bacteria, there are always a few individuals with
resistance to the antibiotics. In an environment containing the antibiotic, only
the resistant individulas will grow and reproduce. By natural selection, the
strain with resistance to the antibiotic becomes the common type.
A pure culture of bacteria can be tested for
antibiotic resistance by evenly swabbing it over
an agar plate and pressing discs of antibiotic
into the agar. After a period of incubation,
sensitivity or resistance to the antibiotic can be
determined by measuring the zone that forms
around the disc. Large zones mean the bacteria
are sensitive to the drug, small or nonexistent
zones are signs of resistance. (Image Courtesy:
Centers for Disease Control and Prevention.)
Darwin’s Theory of Evolution
DDT resistance in Insects
When DDT was first introduced, it was an effective killer of
insects, including mosquitos. However, a small proportion of
insects in various insect populations possesed a natural
resistance to DDT.
When the DDT – sensitive members of a
population were killed by spraying, the DDTresistant insects survived and passed on their
natural DDT-resistance to their offspring.
Evetually, many insect populations were
completely resistant to DDT.
DDT did not create the resistance of the
insects. Rather, the DDT acted as the
environmetal agent for the selection of the
resistant strains.
Darwin’s Theory of Evolution
6. Speciation: Over many generations,
favorable adaptations gardually accumulate
in the species and unfavorable ones
disappear.
Eventually, the accumulated changes
become so great that the net result is a new
species.
The formation of new species is called
speciation.
Geographical and Reproductive
Isolation
Isolation refers to anything that prevents two
groups within a species from interbreeding.
Isolating agroup of organisms seperates its
gene pool from the gene pool of the rest of
the species. Through mutation, genetic
recombination and natural selection, a
different gene pool will evolve in each group.
New species
population
Geographical
isolation
Mutations,genetic
recombinations,
natural selection
Geographical and Reproductive Isolation
Geographic isolation occurs
when a population is divided by
a natural barrier, such as
mountain, desert, river or other
body of water, or a landslide
caused by an earthquake.
As a result, the gene pool of
each group becomes isolated.
Over a period of time, each
group will become adapted to
its particular environment.
Geographical and Reproductive Isolation
When the differences between the
isolated groups become great
enough, they will no longer be able
to interbreed, even if they could get
together.
Fruit fly experiment suggests that
isolating populations in different
environments (e.g., with different
food sources) can lead to the
beginning of reproductive isolation.
These results are consistent with
the idea that geographic isolation is
an important step of some
speciation events.
Geographical and Reproductive Isolation
The Kaibab and Abert squirrel are formed by geographic and reproductive isolation.
The Kaibab squirrel inhabits the north side of Grand canyon and the Abert squirrel
south side. These two squrriel are thoght to be evolved from a common ancestor
whose population was divided by Grand Canyon.
After a long period of geographical isolation, these squirrels evolved. Although they
are similar in appearance but they cannot interbreed.
Geographical and Reproductive Isolation
Differences may arise in
courtship behavior, times of
mating, or the structure of the sex
organs.
Geographical and Reproductive Isolation
Events after
mating like,
inability of
sperm to
fertilize eggs,
the death of
the embryo, or
the
development
of offspring
that are sterile.