Sinh hoc CDDH

Darwin & Natural
Selection
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Charles Darwin
(1809-1882)

Lecturer: PhD.La Viet Hong
Presented by:
1.Nguyen Phuong Thao
2.Le Minh Tuan
3.Tran Thi Huong
4.Nguyen Tu Huong


Charles Darwin
-Charles Robert Darwin (1802-1882).
-He is father of Evolution.
-Proposed a mechanism for evolution, natural
selection
-Darwin went on a 5-year trip around the
world on the ship, the HMS Beagle
-As the ship’s naturalist, he made
observations of organisms in South America
and the Galapagos Islands.
-Darwin published his book «On the Origin of
Species by Means of Natural Selection» in
1859.


What is the natural selection ?

A process through which species that are best suited to
their environment survive and reproduce at a higher rate
than other members of the species.


What is the object of natural selection ?
It is individual and population


The essence of Darwin’s theory of natural selection
(1) Variation exists in natural populations
(2) Many more offspring are born each
season than can possibly survive to maturity
(3) As a result, there is a struggle for
existence
(4) Characteristics beneficial in the struggle
for existence will tend to become more
common in the population, changing the
characteristics of a species
(5) Over time, and given a steady input of new variation into
a population, these processes lead to the emergence of
new species


What are the four parts of natural selection?

Darwin’s Theory of Natural Selection occurs in
four steps:

1.

2.
3.
4.

Overproduction
Variation
Variation
Selection


Overproduction
Each species produces more offspring that can
survive


Variation
Each individual has a unique combination of
inherited traits.

Adaptation: an inherited trait that
increases an organism’s chances of survival


Competition
-Individuals COMPETE for limited resources:
food, water, space, mates.
-Natural selection occurs through “Survival of
the fittest”
Fitness: the ability to survive and reproduce
-Not all individuals survive to adulthood

Selection
-The individuals with the best traits / adaptations
will survive and have the opportunity to pass on it’s
traits to offspring.
+Natural selection acts on the phenotype (physical
appearance), not the genotype (genetic makeup)
+Example: When a predator finds its prey, it is
due to the prey’s physical characteristics, like color
or slow speed, not the alleles (BB, Bb).


-Individuals with traits that are not well suited to their
environment either die or leave few offspring.
-Evolution occurs when good traits build up in a
population over many generations and bad traits are
eliminated by the death of the individuals.


The result of natural selection

From 1 species to 14 species…

-The survival of the most adaptive individuals or the formation of
Warbler finch
Cactus finch
adaptive features of the organisms
Woodpecker finch

Small
ground
finch

Cactus
eater

s
he
nc

Tre
e fi
nc
he
s

Warb
finch

fi
nd
ou
Gr

Small
insectivorous
tree finch
Large
insectivorous

tree finch

Sharp-beaked
Formation
of finch
new species

N
se atur
lec al
tio
n
ler

Insect eaters
Seed eaters

Vegetarian
tree finch

variation

Bud eater

natural selection for best
survival & reproduction

Medium
ground
finch

Large
ground
finch


The role of natural selection


How many are type of natural selection?
The natural slection has 4 type:
1. Stabilizing selection
It occurs when the intermediate or average form of
a trait is selected. Stabilizing selection operates to
eliminate extreme traits.


2. Directional selection
Directional selection is when one extreme form of a trait
is favored or selected.


3.Disruptive Selection




Disruptive Selection is
a form of selection that
selects for the two
different extreme forms

of a trait and selects
against the average form
of a trait.
In this example, both
extremes use mimicry as
a camouflage strategy


4. Sexual selection
-Some forces of selection do not enhance an organism's
fitness or ability to survive, but rather advertise an
organism's health or dominance.
-This type of selection is called sexual selection


Frequency of
individuals

Original population

Original
population

Evolved
population

Stabilizing selection

Phenotypes (fur color)

Directional selection

Disruptive selection


The Hardy-Weinberg Principle






In 1908, English mathematician Godfrey
Hardy and German physician Wilhelm
Weinberg developed an equation that
demonstrates how allele frequencies will
most often remain stable unless acted
upon by certain outside forces or
circumstances.
In other words, they mathematically
demonstrated how and when natural
selection takes place.
The Hardy-Weinberg principle can be
written algebraically by the following


Hardy Weinberg Equation