CLASSE 5^B

Prof. A. Le Piane

Prof. F. Minissale

Darwin’s theory of evolution

by natural selection

Percorso interdisciplinare di avviamento al CLIL

Theory of Evolution

Evolution: the process of changeover time

Specifically, a change in the frequency of a gene or allele in a population over time

Charles Darwin (1809-1882)

Father of Evolutionism

He proposed the theory ofevolution by natural selection

Darwin went on a five-year-long voyage to the SouthSeas aboard The Beagle

He was a naturalist and studiedorganisms in South Americaand the Galapagos Islands

He published his theory in a book: “On the Origin

of Species by Means of Natural Selection” (1858)

Darwin’s voyage to the South Seas

(1831-1836)

Natural Selection

Natural selection is a process which

allows organisms that are best

adapted to an environment to survive

and reproduce more than others.

Darwin’s theory of evolution by natural

selection is based on six points:

Overproduction

Competition

Variation

Selection

Adaptation

Speciation

1. Overproduction

Each species produces more

offspring that can survive

EXAMPLES:

Fish that lay millions of eggs, sea

turtles.

Sea turtles lay from 70 to 190 eggs

(depending on the species). Only

about 1 out of 100 survive.

2. Competition

Because of overpopulation, organisms of the

same species, as well as those of different

species, must compete for limited resources

such as food, water and a place to live.

Interspecific competition – between different species

Intraspecific competition – between the same species

3. Variation

Differences occurring among

members of the same species.

Each individual has a unique

combination of inherited traits.

No two individuals are exactly

alike.

These variations are passed

onto the next generation.

Why is Variation important?

Because the environment changes.

The more variation within a species,the more likely it will survive

EX: If everyone is the same, they are allvulnerable to the same environmentalchanges or diseases

The more variation of types ofspecies in an habitat, the more likelyat least some will survive

EX: Dinosaurs replaced by mammals

Which community has a better chance

of surviving a natural disaster?

Community A Community B

4. Selection

The individuals with the best traits /

adaptations will survive and have the

opportunity to pass on its traits to offspring.

Natural selection acts on the phenotype

(physical appearance), not the genotype

(genetic makeup)

Ex: 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 in a species with good traits that

give them an advantage are better able to

compete, survive and reproduce.

Individuals with bad traits that are not well

suited to their environment either die without

leaving offspring or leave few offspring.

Natural selection occurs through “Survival

of the fittest”

Fitness: the ability to survive and reproduce

Survival of the Fittest

5. Adaptation

The accumulation of characteristics that

improve a species’ ability to survive

over long periods of time.

Allows organisms to become better

suited to their environment.

There are three broad categories of

adaptations:

1. Physiological

2. Behavioural

3. Structural

1. Physiological

Physiological adaptations involve what is going

on inside the body.

Examples: - hibernation of bears.

- cow’s ruminant digestive system.

- pesticide-resistant insects.

- antibiotic resistant bacteria.

2. Behavioural

An organism’s behaviour may provide it with a better chance of surviving and reproducing.

Examples: - Storage of nuts by squirrels.- Plants bending towards light.- Animals “playing dead”.- Migration of Canada geese.

3. Structural

Structural adaptations involve an organisms anatomy.

Examples:- Webbed feet of ducks for swimming.- Talons on eagles for grasping.- Camouflage: this can be used to benefit

both predator and prey.- Mimicry.

Example of camouflage

Phasmatodea (walking stick insect)

Example of mimicry

Moth resembles owl to “scare off” predators.

6. Speciation

Origin of new species.

Over numerous generations, new species

arise by the accumulation of inherited

variations.

When a type is produced that is

significantly different from the original,

it becomes a species.

A species can reproduce successfully

with its own kind.

Evidence for Evolution:

Fossil Record

Homologous Body Structures

Vestigial Organs

Similarities in Embryology

Biochemical Evidence

The Fossil Record

Fossils: a record of

the history of life on

earth

Fossils provide evidence of the history of life on earth and they show how different groups of organisms have evolved over time

Homologous Body Structures

Homologous

Body Structures:

similar anatomy in

different types of

animals because

of a common

ancestry

e.g. wing of bat, human arm,

leg of turtle

Homologous Body Structures

Homologous Body Structures

Vestigial Organs

Vestigial Organs: traces of homologous

organs in other species

Organ that serves no useful functione.g. Appendix

Similarities in Embryology

Embryology: embryos of all vertebrates

are very similar, providing evidence that

they share a common ancestry

Embryological development

Biochemical Evidence

Biochemistry: DNA with more similar

sequences suggests that species are

more closely related

EX: Humans and chimpanzees share

more than 98% of identical

DNA sequences

Learning Goals

1. Define "Evolution" & "Natural Selection".

2. Describe the 6 steps of Natural Selection,

giving an example of each.

3. Explain the importance of "Variation".

4. Does Natural Selection act on an organism

phenotype or genotoype? Explain!

5. List the 5 evidences that support the Theory

of Evolution.