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Lecturer: PhD.La Viet Hong
Presented by:
1.Nguyen Phuong Thao
2.Le Minh Tuan
3.Tran Thi Huong
4.Nguyen Tu Huong
Darwin & Natural Selection
Charles Darwin
(1809-1882)

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:
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
-The survival of the most adaptive individuals or the formation of adaptive features of the organisms
Formation of new species
Natural selection
variation
natural selection for best survival & reproduction
From 1 species to 14 species…
The role of natural selection
How many are type of natural selection?
The natural slection has 4 type:
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
Original population
Original
population
Frequency of
individuals
Evolved
population
Phenotypes (fur color)
Stabilizing selection
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 equation
p2 + 2pq + q2 = 1
Hardy Weinberg Equation
So what does the Hardy-Weinberg Principle Mean?
Natural selection will not occur unless the following situations occur.
A large population becomes small.
Immigration or emigration occurs.
Mating becomes nonrandom.
A specific trait is selected.
A mutation occurs.