EVOLUTION AND NATURAL SELECTION

1. Evolution and
Natural Selection

2. Learning Goals
 1. Define "Evolution" & "Natural Selection".
 2. Describe the 4 steps of Natural Selection, giving an example of each.
 3. Explain the importance of "Variation".
 4. How populations and species respond to environmental changes.
 5. List the 5 evidences that support the Theory of Evolution.

3. 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

4. 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”

5. Darwin’s Finches
 The shape of the beak is adapted to the diet
and environment of the finch.
 Each finch ate a different diet so they
occupied a different niche and created less
competition.

6. Natural Selection
 Natural Selection: Organisms that are best adapted to
an environment survive and reproduce more than others
 Adaptation: an inherited trait that increases an
organism’s chances of survival
 Behavior, Physical, or Physiological traits
 Darwin’s Theory of Natural Selection occurs in four
steps:
 Overproduction
 Variation
 Competition
 Selection

7. What adaptations do
you see?

8. 1. Overproduction
 Each species produces more offspring that can
survive

9. 2. Variation
 Each individual has a unique
combination of inherited traits from
their parents.

10. 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

11. Which community has a better chance of
surviving a natural disaster?
Community A Community B

12. 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

13. 4. Selection
 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)

14.  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.

15. Adaptations

16. Natural Selection:
The process by which organisms that can adapt to
changes in their environment are able to survive and
reproduce.

17. Natural Selection and Adaptations
Natural selection is not random. It occurs in
response to environmental changes and results in
adaptation by advantageous traits being passed on.
Mutations are random.

18. Adaptations:
Changes in structure or behavior of populations to
become more suited to an environment through
natural selection.

19. Structural Adaptations:
A trait in an organism’s body that helps it to survive
in its environment. (Physical)
Ex: camouflage, specialized structures, body parts,
etc.

20. Examples:
Giraffes eat from tall trees instead of the
shorter ones where all other animals eat.
Zebras eat from the top part of the grass
Wildebeest eats the leaves,
Gazelles eat the rest of what's left.
Structural Adaptations:
Some reduce
competition for resources.

21. Examples:
Great Potoos are birds that
hide from predators
Bush Crickets hide from
predators
Lions hide from their prey
to sneak up
Structural Adaptations:
Some provide
camouflage from
predators or prey

22. Examples:
Armadillos have armor and
can roll up
Puffer Fish have spikes and
poison
Bees have a stinger to
protect the hive
Structural Adaptations:
Some provide body
Protection to make them
harder to eat

23. Behavioral Adaptations:
An action an organism takes to help it survive in an
environment.
Ex: Group behavior, migration, hibernation, etc.

24. Types of Behavior
Innate Behavior: A behavior that an organism is born with (Inherited)
*
Learned Behavior: A behavior that an organism acquires through
experience, teaching, or practice

25. Group Behavior Benefits:
1. Protection from predators
2. Hunting packs- more efficient at capturing prey
3. Reproductive Efficiency – mates found within pack or herd, care
for young together

26. Examples of Group Behavior:

27. Flocking

28. Migration

29. Herding

30. Schooling

31. Cooperative Hunting

32. Environmental Changes
and Natural Selection
 The environment is always changing. Organisms that
are adapted to the environmental change will survive
and reproduce.
 Populations can change/shift due to the environmental
change.

33.  3 Population Responses to
Environmental Change:
 Gradual Change-
 1) Population Shift - increase in the amount of
individuals with favorable traits
 2) Speciation - emergence of a new species
through new, specialized adaptations
 Sudden Change-
 3) Death in that area or extinction

34.  Gradual Response #1
 Population evolution or increase in those with a favorable
trait
 Population overall has a greater chance of survival
 Population shift
 Examples: Peppered Moth, Rock Pocket Mouse, Bacteria
resistance

35. Peppered Moth
 Which moth will the bird catch?
 What would happened to the population
of moths?
A
B

36.  Gradual Response #2
 Speciation or a group within a species separates from other
members of its species and develops its own unique
 This can occur do to reproductive isolation (geographic barriers)
 Species: A group of closely related organisms that are able to
reproduce fertile offspring.
 Speciation results when individuals no longer recognize each
as the same species and no longer reproduce with each other.

37. Examples: Grand canyon squirrel, Island birds, fruit flies

38.  Response #3 - Sudden Response
 No time to adapt leads to death of the species
in that area or extinction of the species if a
area.
 Example: Whooly mammoths after Ice Age

39. Types of Natural Selection

40. Type 1

41. Type 2

42. Type 3

43. Evidence for Evolution:

44. Common Descent
 Common Descent – describes how a group of
organisms share a most recent common ancestor.

45. Cladogram: Shows evolutionary relationships, common ancestry,
and derived characters.
Derived Character: Traits that species share and have in common.
Closely related organisms share more characteristics.
Example: All mammals have certain characteristics in common, like
hair, live birth, and produce milk for young.

46. Evidence for Evolution:
 Fossil Record
 Comparative Anatomy
 Embryology
 Genetic Evidence

47. The Fossil Record
 Fossils:
 A record of the history of life on Earth
 Can see organisms that lived in the past and how they
are related to today’s organisms

48. Archaeopteryx
 Missing link between reptiles
and birds

49. Pangea

50. Comparative Anatomy
 Homologous Body Structures: similar in structure, but
different functions, in different types of animals because of
common ancestor
 Example: Human, Horse, Dolphin, Bat have same bone
structure and are all mammals.

51. Comparative Anatomy
 Analogous Body
Structures: similar in
function, but
different structure, in
different types of
animals with no
common ancestor.
 Example: Birds, Bats,
and Insects have
wings for flight, but
do not share a
common ancestor.

52. Comparative Anatomy
 Vestigial Structures: “leftover” traces of evolution
that serve no purpose or function.
 Example: Whales have hipbones, but serves no
function.

54. Embryology
 Embryology: embryos of all vertebrates are very
similar early on – gill slits and tails.
 Example: Fish, Reptile, Bird, and Human look the
same as early embryos.

56. DNA Comparison
 DNA with more similar sequences suggest species
are more closely related.
 EX: Humans and chimpanzees share more than 98%
of identical DNA sequences
 Comparing DNA sequences is more accurate for
determining who is more closely related than body
structures.