Darwin & Natural Selection
Unit 10
Evolution
Learning Goals
▪ 1. Define "Evolution" & "Natural
Selection".
▪ 2. Describe the 5 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.
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
▪ 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
•Wrote a book, “Origin of the Species”
Darwin’s Finches
Natural Selection
▪ Natural Selection: Organisms that are
best adapted to an environment survive
and reproduce more than others
▪ Darwin’s Theory of Natural Selection
occurs in five steps:
• Variation exists within a population
• Some variations favor survival of an
organism
• Overpopulation leads to competition
• Survivors may pass down favorable
traits
• Long periods of time allow for small
changes to accumulate & contribute to
survival adaptations
1. Variation
▪ Each individual has a unique
combination of inherited traits.
▪ Adaptation: an inherited trait that increases an
organism’s chances of survival
▪ 2. Some variations favor the
survival of an organism
What adaptations do
you see?
What adaptations do
you see?
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
3. Overpopulation leads to
Competition
▪ Each species produces more
offspring that can survive
3. 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
4. Survivors may pass down
favorable traits
▪ 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)
• 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)
5. Long periods of time lead to small
changes in a population
▪ 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.
Peppered Moth
A
▪ Which moth will the bird catch?
B
Descent with Modification
▪ Descent with Modification – each
living species has descended, with
changes, from other species over
time.
▪ Common Descent – all living
organisms are related to one another
Evidence for Evolution:
▪
▪
▪
▪
▪
Fossil Record
Homologous Body Structures
Vestigial Organs
Embryology
Biochemical Evidence
The Fossil Record
▪ Fossils: a record of the history of life
on Earth
Archaeopteryx
▪ Missing link between
reptiles and birds
Homologous Body
Structures
▪ Homologous Body
Structures: similar
anatomy in
different types of
animals because
of common
ancestor
Vestigial Organs
• Vestigial Organs: “leftover” traces of
evolution that serve no purpose
Embryology
▪ Embryology: embryos of all
vertebrates are very similar early on
Biochemical Evidence
▪ Biochemistry: DNA with more similar
sequences suggest 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 5 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.
Coral Snake
(Poisonous)
Milk Snake
(Not
poisonous)
Stick Mantid
Flower Mantid