Fig. 22-2

American Revolution French Revolution U.S. Civil War1900185018001750

1795

1809

1798

18301831–1836

1837

1859

18371844

1858The Origin of Species is published.Wallace sends his hypothesis to Darwin.

Darwin begins his notebooks.Darwin writes essay on descent with modification.

Darwin travels around the world on HMS Beagle.

Malthus publishes “Essay on the Principle of Population.”

Lyell publishes Principles of Geology.

Lamarck publishes his hypothesis of evolution.

Hutton proposes his theory of gradualism.

Linnaeus (classification)

Cuvier (fossils, extinction)Malthus (population limits)

Lamarck (species can change)

Hutton (gradual geologic change)

Lyell (modern geology)

Darwin (evolution, natural selection)

Wallace (evolution, natural selection)

Evolution Unit Lecture Part I Ch 22,23

Theory: fact based

Darwin’s proposed mechanism, natural selection, explained the observable patterns in evolution

* artificial selection• Observation #1: Members of a

population often vary greatly in their traits (snails)

• Observation #2: Traits are inherited from parents to offspring

• Observation #3: All species are capable of producing more offspring than their environment can support (puffball fungus)

• Observation #4: Owing to the lack of food or other resources, many of these offspring do not survive.

• Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring that other individuals.

• Inference #2 This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

Fig. 22-10

Fig. 22-11

Sporecloud

Natural Selection: A Summary

• 1. NS is a process in which individuals that have certain heritable characteristics survive and reproduce at a higher rate than other individuals

• 2. Over time, NS can increase the match between organisms and their environment

Fig. 22-12

(b) A stick mantid in Africa

(a) A flower mantid in Malaysia

• 3. If an environment changes, or if individuals move to a new environment, NS may result in adaptation to these new conditions, sometimes giving rise to new species in the process

• “INDIVIDUALS DO NOT EVOLVE!”

• POPULATIONS EVOLVE OVER TIME

Fig. 22-13

Predator: Killifish; preysmainly on juvenileguppies (which do notexpress the color genes)

Guppies: Adult males havebrighter colors than thosein “pike-cichlid pools”

Experimentaltransplant ofguppies

Pools withkillifish,but noguppies priorto transplant

Predator: Pike-cichlid; preys mainly on adult guppies

Guppies: Adult males are more drab in colorthan those in “killifish pools”

Sourcepopulation

Transplantedpopulation

Sourcepopulation

Transplantedpopulation

Nu

mb

er o

fco

lore

d s

po

ts

Are

a o

f co

lore

dsp

ots

(m

m2 )

1212

1010

88

6 6

4 4

22

0 0

RESULTS

EXPERIMENT

Evidence

• Direct observations of Evolutionary Change (predation, HIV resistance)

• Fossil record (transition fossils)

• Homology (common ancestry)embryology, vestigial structures and genetic: hox genes (gene conservation)

• Biogeography

Fig. 22-15

Bristolia insolens

Bristolia bristolensis

Bristolia harringtoni

Bristolia mohavensis

Latham Shale dig site, SanBernardino County, California

Dep

th (

met

ers

)

0

2

4

6

8

10

12

14

16

18

1

2

3

3

1

2

44

Fig. 22-16

(a) Pakicetus (terrestrial)

(b) Rhodocetus (predominantly aquatic)

(c) Dorudon (fully aquatic)

Pelvis andhind limb

Pelvis andhind limb

(d) Balaena (recent whale ancestor)

Fig. 22-17

Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

Human WhaleCat Bat

Fig. 22-18

Human embryoChick embryo (LM)

Pharyngealpouches

Post-analtail

Fig. 22-19

Hawks andother birds

Ostriches

Crocodiles

Lizardsand snakes

Amphibians

Mammals

Lungfishes

Tetrapod limbs

Amnion

Feathers

Homologouscharacteristic

Branch point(common ancestor)

Te

trapo

ds

Am

nio

tes

Bird

s

6

5

4

3

2

1

Fig. 22-20

Sugarglider

Flyingsquirrel

AUSTRALIA

NORTHAMERICA

EVOLUTION OF POPULATIONS Adapt, Migrate or Die

• Genes Mutate

• Individuals are selected

• Populations Evolve

Fig. 23-3

13.17 19 XX10.169.128.11

1 2.4 3.14 5.18 6 7.15

9.10

1 2.19

11.12 13.17 15.18

3.8 4.16 5.14 6.7

XX

Geographic variation

Genetic variation

Fig. 23-4

1.0

0.8

0.6

0.4

0.2

046 44 42 40 38 36 34 32 30

GeorgiaWarm (21°C)

Latitude (°N)

MaineCold (6°C)

Ldh

-B b

alle

le f

req

uen

cyCLINE

How do we measure evolution?

• The smallest unit of measure is an allele.

• Variation in a population – measured at the nucleotide level or gene level

Hardy Weinberg equation• * can be used to test whether a population

is evolving

• * 2 independent mathematicians

Fig. 23-6

Frequencies of alleles

Alleles in the population

Gametes produced

Each egg: Each sperm:

80%chance

80%chance

20%chance

20%chance

q = frequency of

p = frequency of

CR allele = 0.8

CW allele = 0.2

Fig. 23-7-1

SpermCR

(80%)

CW

(20 %

)

80% CR ( p = 0.8)

CW (20%)

20% CW (q = 0.2)

16% ( pq) CRCW

4% (q2) CW CW

CR

(80%

)

64% ( p2) CRCR

16% (qp) CRCW

Eg

gs

Fig. 23-7-2

Gametes of this generation:

64% CRCR, 32% CRCW, and 4% CWCW

64% CR   +    16% CR    =   80% CR = 0.8 = p

4% CW     +    16% CW   =   20% CW = 0.2 = q

Fig. 23-7-3

Gametes of this generation:

64% CRCR, 32% CRCW, and 4% CWCW

64% CR   +    16% CR    =   80% CR = 0.8 = p

4% CW     +    16% CW   =   20% CW = 0.2 = q

64% CRCR, 32% CRCW, and 4% CWCW plants

Genotypes in the next generation:

Fig. 23-7-4

Gametes of this generation:

64% CR CR, 32% CR CW, and 4% CW CW

64% CR    +     16% CR    =   80% CR  = 0.8 = p

4% CW      +    16% CW    =  20% CW = 0.2 = q

64% CR CR, 32% CR CW, and 4% CW CW plants

Genotypes in the next generation:

SpermCR

(80%)

CW

( 20%

)

80% CR ( p = 0.8)

CW (20%)

20% CW (q = 0.2)

16% ( pq) CR CW

4% (q2) CW CW

CR

(80%

)

64% ( p2) CR CR

16% (qp) CR CW

Eg

gs

HW continued

• Significant change = allele frequency shift = evolving population

• Consider PKU 1 in 10000 in the US • If all assumptions hold for PKU then the

frequency of individuals in the population born with PKU will correspond to q2

• PKU demonstrates that harmful recessive alleles can be concealed in a pop due to heterozygotes

• PKU cannot breakdown phenylalanine

5 conditions for HW

• 1. No mutations:

• 2. Random mating

• 3. No natural selection

• 4. Extremely large population size

• 5. No gene flow

Fig. 23-8-3

Generation 1

CW CW

CR CR

CR CW

CR CR

CR CR

CR CR

CR CR

CR CW

CR CW

CR CW

p (frequency of CR) = 0.7q (frequency of CW

) = 0.3

Generation 2

CR CWCR CW

CR CW

CR CW

CW CW

CW CW

CW CW

CR CR

CR CR

CR CR

p = 0.5q = 0.5

Generation 3p = 1.0q = 0.0

CR CR

CR CR

CR CR

CR CR

CR CR

CR CR CR CR

CR CR

CR CR CR CR

Natural selection, genetic drift and gene flow can alter allele frequencies in a pop

Genetic drift

• Chance events can cause allele frequencies to fluctuate unpredictably from one generation to the next especially in small population

Founder’s Effect

• When a few individuals become isolated from a larger population, this smaller group may establish a new population whose gene pools differs from the source population

Fig. 23-9

Originalpopulation

Bottleneckingevent

Survivingpopulation

Fig. 23-10

Numberof allelesper locus

Rangeof greaterprairiechicken

Pre-bottleneck(Illinois, 1820)

Post-bottleneck(Illinois, 1993)

Minnesota, 1998    (no bottleneck)

Nebraska, 1998    (no bottleneck)

Kansas, 1998    (no bottleneck)

Illinois

1930–1960s

1993

Location Populationsize

Percentageof eggshatched

1,000–25,000

<50

750,000

75,000–200,000

4,000

5.2

3.7

93

<50

5.8

5.8

5.3 85

96

99

(a)

(b)

Effects of Genetic Drift

• 1. Significant in small populations

• 2. Can Cause allele frequencies to change at random

• 3. can lead to a loss of genetic variation within populations

• 4. can cause harmful alleles to become fixed

Fig. 23-11

Gene Flow

• The transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes

• Gene flow tends to reduce the genetic differences between populations

• Single population with a common gene pool