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Darwin & Natural Selection
Theory of Evolution
 Evolution is the process of change in
all forms of life over generations.
 It suggests that all life has common
ancestors.
 Evolution can be seen in small
changes over a (relatively) short
period of time or massive changes
over an extremely long period of
time.
Charles Darwin
 Charles Darwin was an English naturalist
who, in the mid 1800s, developed a theory
of how evolution works.
 A naturalist is a person who studies plants
and animals by observing them.
 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
So what does this mean?
 Individuals in a population have variations.
 A variation is a slight difference in an inherited
trait of individual members of a species.
 Variations arise naturally in populations, occurring
in offspring as a result of sexual reproduction.
 Genetic changes can be passes on to future
generations.
 This can lead to totally new species!
Natural Selection
 Natural Selection is the process by which
populations of organisms with variations
that help them survive in their environments
live longer, compete better, and reproduce
more than those that do not have the
variations.
 Natural selection explains how populations
change as their environments change.
Darwin’s Theory of Natural Selection
 Darwin proposed the theory that
evolution happens through a process
that he called natural selection
 This process has four parts:
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Overproduction
Variation
Competition
Selection
1. Overproduction
 Each species produces more
offspring that can survive
2. Variation
 Each individual has a
unique 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?
 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 in the types of
species in an habitat, the more likely
at least some will survive
 Ex: Dinosaurs replaced by mammals
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
 Due to limited resources, not all offspring
will survive.
4. Selection
 The individuals with the best traits / adaptations will
survive and have the opportunity to pass on it’s
traits to their offspring.
 Ex: When a predator finds its prey, it is due to
the prey’s physical characteristics, like color,
size, or slow speed,
 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
Evidence for Evolution:
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Fossil Record
Homologous Body Structures
Vestigial Organs
Embryology
Biochemical Evidence
The Fossil Record
 Fossils: a record of the history of life
on Earth
Homologous Body Structures
 Homologous
Body Structures:
similar anatomy in
different types of
animals because
of common
ancestor
Vestigial Structures
 Vestigial Structures are body parts that
have lost their original function through
evolution and no longer serve a purpose.
Embryology
 the science of the development of
embryos from fertilization to birth is
called Embryology
All vertebrate embryos exhibit pharyngeal
pouches at certain stages of their development.
These features, which develop into neck and
face parts, suggest relatedness.
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