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EVOLUTION AND
NATURAL SELECTION
Question 6
Evolution
• Evolution is change over time.
• The Theory of Evolution explains how living things descended (come
from) from earlier organisms
• A scientific theory is NOT just a belief, it is a well-supported tested
explanation.
• Lots of Evidence Supports Evolution
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Fossils
Similarities in DNA and protein
Similarities in Body Structure
Similarities in Early Development
Pg. 357- 361
Who?
•Charles Darwin AND Alfred Wallace
are credited with developing the
Theory of Evolution.
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
Alfred Wallace - Discoveries
•Founder of
biogeography
•“Wallace Line”:
imaginary line
separating Asia
and Australia
Evidence for Evolution:
Fossils
• Fossils provide a look into the past
• Scientists can trace how a species
have changed.
• Fossils show that an Eohippus has 4
toes on its hooves. A modern day
horse has one toe on its hooves.
Evidence for Evolution:
Early Development
•Similarities among embryos
in development allow
scientist to infer
evolutionary relationships.
•Animals that are more
closely related are more
similar in development.
Evidence for Evolution: Similarities in body Structure
• Homologous Structures
• traits that are similar in different species because the species share a
common ancestor.
• Ie. Arm, fin and wing may have evolved from the forelimb of a common
vertebrate.
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 four steps:
•Overproduction
•Variation
•Competition
•Selection
1. Overproduction
• Each species produces more offspring that can survive
2. Variation
Each individual has a different
combination of inherited
traits.
 Adaptation: an inherited
trait that increases an
organism’s chances of
survival
What adaptations do
you see?
What adaptations do
you see?
Why is Variation Important?
Variation is 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
3. Competition
Individuals COMPETE for limited resources and the ones
that survive will pass on their traits.
Natural selection occurs through “Survival of the fittest”
 Fitness: the ability to survive and reproduce
Not all individuals survive to adulthood
4. Selection
The individuals with the best traits / adaptations
will survive and pass on their genes to their
offspring
Natural selection acts on the phenotype (physical
appearance), not the genotype (genetic makeup)
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.