OBJECTIVES:

At the end of the lesson, the students are

expected to:
a. define evolution and describe how it takes
place;
b. determine and explain the theoretical ideas
about evolution
c. discuss the evolutionary patterns, the pace of
evolution and the evolution of man;
d. appreciate the history of one’s beginning; and
1.Whenever you hear the word
evolution, what comes first into your
mind?

2.Can you please give a word that is

related to evolution!
 What is Evolution?
Evolution
- refers to a change in a population of
organisms over time.
- is change in the heritable characteristics of
biological populations over successive
generations.
- is the change in the characteristics of a
species over several generations and relies on
the process of natural selection.
 When we say evolution, it can be
proven with pieces of evidence; can
be explained through the theory of
natural selection and is seen from
changes in species.
 When we say evidences, it can be
direct or indirect. But scientists
combined these evidences to show that
organisms change and establish
relationships with other species.
 Direct evidence of evolution can
usually be observed in places where
one can examine actual changes in a
population of organisms within a
particular period of time.
 Indirect evidence is evidence that
establishes immediately collateral
facts from which the main fact may be
inferred. are:
Examples
- fossils
- anatomical evidence
- embryological evidence
- biochemical/chemical evidence
 What are fossils?
Fossils
- are preserved remains of an organism
- are formed when the whole or a part
of the organism is buried
- are often incomplete because only the
hard parts of an organism become
fossils and the soft tissues either decay
or eaten away.
 Embryological Evidence?
Scientists noted that at some point
during the development, the embryos of
many different animals appear so similar
that it is difficult to tell them apart.
However, the similarities in the early
stages of embryonic development are
further evidence that living things evolved
and that they share a common ancestry.
 Anatomical Evidence?
Comparing the body structures of
living species also provided scientists
with clues pointing to evolution and the
common ancestry of organisms.
Similarities in terms of shapes and
arrangement of bones among them
indicate that they evolved from a
common ancestor.
Biochemical/Chemical Evidence
Fossil records allow scientists to make
a prediction and test it. Biochemical
findings also provide evidence that
supports the idea that if species changed
overtime, then the genes that determine
their characteristics were also altered.
Scientists also used DNA comparison to
show relationships among organisms.
 What is Natural
Selection?
Natural selection attempted to
explain the causes of evolutionary change.
It is the differential survival and
reproduction of individuals due to
differences in phenotype. It is a key
mechanism of evolution, the change in the
heritable traits characteristics of a
population over generations.
The theory has been divided into five
parts, each of which explains how
evolution happens.
1. Overpopulation
2. Struggle for existence
3. Presence of variation
4. Survival of the fittest
5. transmission of variations
 Overpopulation
The number of offspring is
usually greater than the available
resources necessary for organisms
to survive. Organisms can die from
many causes – disease, starvation or
being eaten by predators. The
environment cannot support every
organism. Many die before they can
reproduce.
 Struggle for
Existence
Every organism must struggle
to survive. One reason that organisms
survive is that they must to compete
for limited resources including food,
territory and other necessities of life.
They also struggle to elude predators
and to overcome diseases.
 Presence of Variation
There is variation within a
species. Traditionally, a species
refers to a group of organisms that
share similar characteristics and inter
breed to produce fertile offspring.
 Understanding how individuals of the
same species vary was the key to
Darwin developing his theory. Because
the environment changes, the more
variation within a species, the more
likely it will survive.
 Survival of the Fittest
Some variations allow members
of a species to survive and
reproduce better than others. The
individuals with the best traits /
adaptations will survive and have the
opportunity to pass on its traits to
offspring.
 Variations can be transmitted
Organisms that survive and
reproduce pass on their traits to their
offspring and helpful traits gradually
appear in more and more of the
population. These traits enable organism to
fit into their environment while those who
lack these variations slowly die off. If more of
the population has the advantageous trait,
more and more of succeeding generations
 There are four factors that made
changes in species possible and they are
as follows:
1. Occupancy of empty niches
2. Migration
3. Isolation
4. Genetic recombination
 Occupancy of empty niches
The formation of new species is
affected by competition among
organisms. Every type of organism
needs food, shelter and water to
survive. These needs, along with the
organism’s habitat and its role in that
habitat comprise the organism’s
niche.
 When two organisms occupy the
same niche, they compete for the same
needs. One species will survive and the
other will not. But when two organisms
occupy different niches, they both have
a better chance for survival.
 Migration
Migration is the movement of
populations, groups or individuals. In
genetic terms, migration enables gene flow:
the movement of genes from one population
into another. If the two populations
originally had different gene frequencies
and if selection is not operating, migration
alone will rapidly cause the gene
frequencies of the different populations to
 Isolation
The division of a single population
into two or more groups because of
some barrier for interbreeding is called
isolation. It occurs when some members
of species are suddenly separated from
the rest of the species.
 There are two mechanisms of
speciation by isolation: geographic and
reproductive isolation.
In geographic isolation, a portion
of an existing population becomes totally
isolated because of geographic barriers like
a mountain range, a river valley, an ocean
or a desert.
 It is important to note, however, that
separation of species into two or more
isolated subpopulations is not enough to
generate new species. The separation
must continue for several generations, so
that genetic differences will accumulate
and a new species will arise.
 In reproductive isolation, also
known as genetic isolation, isolated
populations have become so genetically
different that reproduction can no longer
occur even if their members are brought
back together and mate
 Genetic Recombination
Recall that species refers to a
population of organisms that share
similar characteristics, interbreed
naturally and produce equally fertile
offspring. An individual, on its own
cannot be a species; one can only be a
member. Gene flow is another way of
looking at the concept of a species.
Theoretical Ideas
About
Evolution
 A number of scientists have explained
how evolution happens and the idea that
organisms change over time was not
initially accepted by the general public.
The majority of people believed in the
biblical story of creation in which all
species had been created by a Supreme
Being.
 The theory of evolution does not
deny the role of a Supreme Being in
creation; rather, it only recognizes that
species have the ability to change over
time in response to environmental
struggles
 The theory of evolution was not widely
accepted for several decades until
theories for its underlying mechanism
became available.

Several theories by scientists and

pieces of evidence explained how and
why evolution occurs.
 Lamarck’s Theory of Evolution
Jean Baptiste Lamarck (1744-1829)
- a French Biologist
- proposed that life evolves or changes
- explained evolution as a process of
adaptation
- known for the Theory of Use and Disuse
- became famous for his Theory of
Inheritance of Acquired
Characteristics
- also known as Lamarckism
rges Cuvier’s Theory of Correlation of P
Georges Cuvier (1769-1832)
- a French Naturalist and Zoologist
- he opposed Lamarck’s theory of evolution.
- known for Essay on the Theory of the
Earth.
- he hypothesized that the emergence and
destruction of a species came about because
of catastrophic events.
- Theory of Catastrophism
 Darwin’s Theory of Natural
Selection
Charles Robert Darwin (1809-1882)
- an English Naturalist and Geologist
- proposed that evolution occurred as the result
of Natural Selection.
- is the process where in heritable traits that
make it more likely for an organism to survive
long enough to reproduce become more
common over successive generations of a
population.
 What does Darwin
believed?
Darwin believed that the needs of
animals have nothing to do with how
they evolve and that changes in an
organism during its lifetime do not affect
the evolution of the species. He said that
organisms, even of the same species, are
all different and that varying traits help
them survive and have more offspring.
Gregor Mendel
- the Father of Genetics
- genetics offer another proof that
Lamarck’s theory is incorrect.
- we know that the only way for traits to
be passed on is through the genes, which
cannot be affected by the outside world.
August Weismann (1893)
- a German Evolutionary Biologist
- changes that occur in normal body cells
are not usually inherited.
- alterations to the genes in the germ
cells produce inheritable variations.
QUIZ