Download Darwin`s theory of evolution by natural selection

Percorso interdisciplinare di avviamento al CLIL
Darwin’s theory of evolution
by natural selection
CLASSE 5^B
Prof. A. Le Piane
Prof. F. Minissale
Theory of Evolution
 Evolution: the process of change
over 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 of
evolution by natural selection
 Darwin went on a five-yearlong voyage to the South
Seas aboard The Beagle
 He was a naturalist and studied
organisms in South America
and 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 all
vulnerable to the same environmental
changes or diseases
 The more variation of types of
species in an habitat, the more likely
at 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)
Survival of the Fittest
 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
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 function
e.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.