1

Chapter 15 Evolution

15-1 Darwin’s Theory of Natural Selection

2

Charles Darwin1809-1882 As a boy liked nature

study Flunked out of med

school Theology degree from

Christ College, Cambridge

Became minister Church of England

1831 job as naturalist on HMS Beagle

5 year world voyage to chart coasts

3

Unique Galapagos Islands 1000 km off west coast

of South America Unique species

animals, similar to S.A. but not exact

Unique species animals on each island, similar to S.A. and each other but not exact

4

Darwin’s Finches Especially interesting

is the number and variety of these birds

Each island had own variety dependent on the food source

5

6

Darwin’s Influenced by:1. Thomas Malthus: human species grows faster

than food supply; competition for food, space, mates, shelter; struggle to survive

2. Pigeon breeding: found individual variation, could breed desirable traits into a population (artificial selection)

3. His 13 children: found individual variation

4. 22 years of study after HMS Beagle to formulate his ideas

7

Natural Selection Is a mechanism for change in a population Groups NOT INDIVIDUALS evolve Occurs when organisms with certain

variations survive, reproduce, and pass their variations onto the next generation

8

Theory of Natural Selection (old)B. Individuals in a

population have variations

D. Overtime, individuals with helpful variations make up more and more of the population

A. Organisms produce more offspring than can survive

C. Individuals with certain helpful variations survive in their environment, reproduce, and pass helpful variation on to offspring

9

Natural Selection (NEW)

Individuals in a population show variations.

Variations can be inherited.

Organisms have more offspring than can survive on available resources.

Variations that increase reproductive success will have a greater chance of being passed on.

15.1 Darwin’s Theory of Natural Selection

10

Origin of Species by Means of Natural

SelectionBy Charles Darwin

Published in 1859

11

Other’s Ideas on Evolution Alfred Wallace: had same ideas about

natural selection as Darwin, but Darwin published first (both presented their ideas in 1858 at a scientific meeting)

Genetics has changed ideas about evolution; now we measure frequency of allele in gene pool

Gene pool: all the genes of a population

12

Chapter 15 Evolution

15-2 Evidence of Evolution

13

Evolution and Natural Selection Darwin’s theory of natural selection is not

synonymous with evolution. It is a means of explaining how evolution

works. The theory of evolution states that all

organisms on Earth are related; share a common ancestor.

14

Evidence for Evolution

1. Fossils2. Anatomy3. Embryology4. Biochemistry5. Geographic Distribution6. Adaptations

15

1. Fossils Record of early life Ancestors of whales

were dog sized land animals

Record is incomplete

16

2. AnatomyA. Homologous structures: similar arrangement or

function or both

Evidence that organisms evolved from a common ancestor

(Analogous structures: body parts do not have common evolutionary origin but have similar function)

17

Homologous Structures

18

2. AnatomyB. Vestigial structures: body part that has no

function today but probably did in ancestor

eyes of blind mole rat

eyes of blind cave fish

wings of flightless birds

human appendix, little toe, muscles to move ears…

19

3. Embryology Embryo: earliest stage

of growth and development

Similarities for all vertebrates Tail Gill slits

Suggest a common ancestor

Gill slits

tail

20

21

4. Biochemistry Comparison of DNA, RNA, and/or proteins Newest RNA evidence is that there are

three types (Domains) of organismsArchae

Prokaryote

Archaebacteria

Eubacteria

Prokaryote

Eubacteria

Eukarya

Eukaryote

Protista

Fungi

Plants

AnimalsAncestral Prokaryote

22

5. Geographic Distribution The distribution of plants and animals that

Darwin saw first suggested evolution to Darwin.

Rabbit Mara

23

5. Geographic Distribution Patterns of migration were critical to Darwin

when he was developing his theory. Evolution is intimately linked with climate

and geological forces. Biogeography is the branch of science that

studies the world distribution of organisms.

24

6. AdaptationsAny variation that helps an organisms’ chance for survival

A. Structural Adaptations: can take millions of years

mimicry: enables one species to resemble another species;

harmless look like harmful

all harmful look alike

25

6. AdaptationsA. Structural Adaptations

camouflage: enables species to blend in with surroundings so that they are not easily found by predators

26

6. AdaptationsB. Physiological adaptations: takes shorter

time

Changes in organisms metabolic processes (function)

antibiotic resistant bacteria

pesticide resistant insects (head lice)

herbicide resistant weeds

27

6. Adaptations Not all features of an organisms are

necessarily adaptive. Example: helplessness of human babies. Human babies are born at a much earlier

stage of development than other mammals. This is probably not an adaptation but a consequence of the larger brains and upright posture of humans.

28

Chapter 15 Evolution

15-3 Shaping Evolutionary Theory

29

Population Genetics and Evolution Darwin knew NOTHING about genes,

never read the work of Mendel even though they lived about the same time

Darwin: 1809-1882 Mendel: 1822-1884

30

Populations NOT individuals evolve

Individuals can’t change their genes, can’t change their genotypes and can’t change their phenotypes or trait

Individuals can only respond to their environments as their genes allow

31

Natural Selection acts on Phenotypes

If an individual has a phenotype that is poorly suited to their environment, the individual organism may not survive

and/or may not reproduce to pass their genes on to the next generation

32

Natural Selection acts on Phenotypes

Each member of a population has the genes that characterize the traits of the species

All the genes (and alleles) of individuals make up the gene pool of the population

Evolution occurs as a population’s genes and their frequencies change over time

33

Allelic Frequency Allelic frequency: % of any specific allele

= Number of specific allele

Total number of alleles

Can change over time or stay the same

34

Hardy-Weinberg Principle Hardy-Weinberg principle states that when

allelic frequencies remain constant, a population is in genetic equilibrium.

35

Hardy-Weinberg Principle Equation: p2 + 2pq + q2 = 1

and p + q = 1

This equation allows us to determine the equilibrium frequency of each genotype in the population.

Homozygous dominant (p2) Heterozygous (2pq) Homozygous recessive (q2)

36

37

Genetic Equilibrium Frequency of alleles stays the same over

many generations

Not evolving

Phenotypes remain the same too

38

Changes in Genetic Equilibrium

1. Mutations2. Genetic Drift3. Gene Flow4. Nonrandom mating5. Natural Selection

39

1. Mutations Caused by environmental factors like

radiation and chemicals Caused by random chance Some mutations are lethal and quickly

eliminated Some mutations are helpful (useful) and

new allele or gene becomes part of the population’s gene pool

40

2. Genetic Drift Alteration of allelic frequency by chance events Small populations that become isolated by natural

events can evolve differently Bottleneck effect: disasters such as earthquakes,

floods kill victims unselectively Founder effect: few individuals colonize an

isolated area (Darwin’s finches)

41

3. Gene Flow Movement of individuals into or out of a

population When individuals immigrate or emigrate

their genes go with them Example: westward expansion in the US

42

4. Nonrandom mating Usually organism

mate with those in close proximity. (May result in inbreeding).

Usually organisms mate with those of the same or similar phenotype.

43

5. Natural Selection Acts on variation Some variations increase or decrease an

organism’s chance for survival Variation can be inherited and are

controlled by alleles

44

5. Natural Selection Four Types of Natural Selection that act

on variationA. Stabilizing Selection

B. Directional Selection

C. Disruptive Selection

D. Sexual Selection

45

Stabilizing Selection Favors average Reduces variation Example: Large

spiders easy to see and be eaten while small spiders have a hard time getting food

46

Directional Selection Favors one extreme Can lead to rapid

evolution Example: Over time

there were more and more darker colored Peppered Moths in the industrial area of England in the 1800’s

47

Disruptive Selection Both extremes are

favored Average (mean)

disfavored Leads to the evolution

of two species Example: Light yellow

butterfly overtime becomes either nearly white or orange

48

Sexual Selection Sexual selection operates in populations

where males and females differ significantly in appearance.

Qualities of sexual attractiveness appear to be the opposite of qualities that might enhance survival.

Example: tail of mail peacocks, while beautiful, makes the organism a greater target for predators.

49

The Evolution of Species Species: group of organisms that look alike

and can breed to produce fertile offspring Speciation: process of evolution of new

species occurs when members of similar populations no

longer interbreed to produce fertile offspring in their natural environment

50

Reproductive Isolation Prezygotic isolation mechanisms make

fertilization unlikely. Can’t mate to produce fertile offspring Genetic differences: genetic material too

different so no fertilization results Behavioral differences: mate at different

times of day or at different season; different “courting” rituals

51

Reproductive Isolation Postzygotic isolation

occurs when fertilization has occurred but a hybrid offspring cannot develop or reproduce.

Prevents offspring survival or reproduction.

Fertilization is possible between a tiger and a lion but the offspring is sterile.

52

Speciation In allopatric speciation a physical barrier

divides one population into two or more populations; geographic isolation.

53

Geographic Isolation Islands, lava flows, rock slides, rivers

changing course Populations become physically separated Over time each small population adapt

differently to environments and have different gene pool

When gene pool becomes too different then two species exist

54

Speciation In sympatric

speciation a species evolves into a new species without a physical barrier.

55

Patterns of Evolution Divergent Evolution (adaptive radiation):

become different Convergent Evolution: become the same Coevolution: the evolution of one species

effects the evolution of another species

56

Divergent Evolution Adaptative radiation::

one ancestral species evolves into many species to fit diverse habitats

57

Convergent Evolution Distantly related

organisms evolve similar traits

Occurs when unrelated species occupy similar environments in different parts of the world

African and American cactus

58

59

Coevolution The relationship

between two species might be so close that the evolution of one species affects the evolution of the other species.

Example: specialized mouth parts

60

Two Theories of Speciation Gradualism: species

originate through gradual, slow change Evolution of the horse

61

Two Theories of Speciation Punctuated

Equilibrium: speciation relatively quickly (10, 000 years) with long periods of no evolution (genetic equilibrium)

High environmental change Evolution of elephants