Evidence for Evolution

Fossil Record Evidence:

Horse evolution

four toes on ground (#2-5), short teeth good for eating soft leaves on shrubs & trees

one toe on ground (#3), long teeth good for eating tough blades of grass

Whale Evolution

Fossil Record of Whale Evolution

Pelvis andhind limb

Rhodocetus (predominantly aquatic)

Pakicetus (terrestrial)

Dorudon (fully aquatic)

Balaena (recent whale ancestor)

Pelvis andhind limb

A lesson in Biogeography

The Wallace Line

http://evolution.berkeley.edu/evolibrary/article/history_16

http://theglyptodon.wordpress.com/2011/05/25/the-wallace-line/

Read this interesting article by Jared Diamond (author of Guns, Germs, and Steel) about “Mr. Wallace’s Line”:http://discovermagazine.com/1997/aug/mrwallacesline1198

Wegener’s contributions to Biogeography

Alfred Wegener found that the distributions of fossils of several organisms supported his theory that the continents were once joined together.

http://evolution.berkeley.edu/evolibrary/article/history_16

Galapagos Finches

Hawaiian Fruit Flies

Humerus

Radius

Ulna

Carpals

MetacarpalsPhalanges

Human Cat Whale Bat

Comparative Anatomy Evidence:Homologous Structures

Comparative Anatomy Evidence:Vestigial Structures

Boa pelvic region

Human Coccyx (tailbone)

Comparative Embryology Evidence

Pharyngealpouches

Post-analtail

Chick embryo Human embryo

Comparative Embryology Evidence

Fig. 13-6

Tetrapod limbs

Amnion

Lungfishes

Feathers

Amphibians

Mammals

Lizardsand snakes

2

Hawks andother birds

Ostriches

Crocodiles

1

3

4

5

6

Am

nio

tes

Tetrapo

ds

Bird

s

Biochemical Evidence: amino acid

sequence of hemoglobin

Biochemical Evidence: amino acid sequence of cytochrome c

Biochemical Evidence: DNA sequence

Microevolution: a change in a population’s

alleles over timeHow do we detect this change? Need to look at a population’s collection of alleles, or its gene pool.

Darwin’s Finches video:

Hardy-Weinberg Theorem

• H-W allows you to predict allele frequencies for a non-evolving population.

• For a population to be in H-W equilibrium, the following must be true:– Population must be very large in size– Population must be isolated from other pops (no

gene flow: no immigration or emigration)– No mutations– Mating must be random– No natural selection (equal chance of survival &

reproductive success)

Any changes to expected allele frequencies over time may indicate that micro-evolution is occurring in the population.

Allele frequencies

Genotype frequencies

Dominanthomozygotes

Heterozygotes Recessivehomozygotes

p + q = 1

p2 + 2pq + q2 = 1

Hardy-Weinberg Theorem

Causes of Microevolution

1. Genetic Drift– Produces random changes to the gene pool of small

breeding populations• An allele may be eliminated from pop by chance

A. Bottleneck Effect: dramatic decr in pop size due to environmental fluctuation (depletion of food supply, disease outbreak)

Examples: Cheetahs, Florida Panthers

B. Founder Effect: when one or a few individuals from a large pop establish a colony (new pop), and bring with them only a small fraction of genetic variation from orig pop

Example: Marine Iguanas in Galapagos

Fig. 13-11a-3

Originalpopulation

Bottleneckingevent

Survivingpopulation

“By 1990s, the endangered Florida panther – a flagship species and one of the last remaining symbols of wilderness in Florida - was in serious trouble. There were fewer than 30 panthers remaining in the wild. The population suffered from several biomedical and morphological abnormalities, including low genetic diversity, heart defects, reproductive dysfunctions and kinked tails. Many of these problems were thought to be indicative of inbreeding, and conservation biologists recommended genetic restoration. This recommendation was controversial but was ultimately implemented after careful planning…”

http://research.ifas.ufl.edu/featured-discoveries/genetic-restoration-saves-endangered-florida-panther#

Causes of Microevolution2. Gene Flow

– movement of alleles by migration of individuals to a new population• Generally increases variation within a population

3. Mutation– Unpredictable change in DNA, a source of new alleles

• Introduces variation in pop• Only inheritable if occurs in gametes• Can be harmful, beneficial, or neutral

4. Natural Selection– Leads to adaptive evol change, as “fittest” indiv survive

to reproduce

Fig. 13-3b

Chromosome with alleleconferring resistanceto pesticide

Additionalapplications willbe less effective, andthe frequency ofresistant insects inthe populationwill grow

Survivors

Pesticide application

Causes of Microevolution

5. Non-random MatingA. Inbreeding: Individuals mate more freq with closely

related individuals• Common in plants in the form of self-fertilization• Not always harmful but sometimes leads to inbreeding

depression (lower fitness: sterility, higher juvenile mortality)

Examples: Cheetahs, Florida Panthers

B. Sexual selection (mate selection): individuals select mates by their phenotype

• Can change genotype frequencies

Examples: Peacocks, Mallards, Humans, etc.

Fig. 13-14a

Fig. 13-UN4

Microevolution

(a)

may result fromchange in allelefrequencies in a

population

is the

(g)

(c)(b)

(d)

(e) (f)

individualsor gametes

best adaptedto environment

adaptiveevolution

random fluctuationsmore likely in a

due tomovement of

may be result of

leads todue to

of individuals

Fig. 13-8

Parents

Offspring,with newcombinationsof alleles

Gametes

Meiosis

´

and

A1

Randomfertilization

A1 A2 A3

A1 A2 A3

A3A1A2A1

Fig. 13-9a

Webbing No webbing

Fig. 13-9b

Phenotypes

320–––500

Genotypes

Number of animals(total = 500)

Genotype frequencies

Number of allelesin gene pool(total = 1,000)

Allele frequencies

WW Ww ww

320 160 20

= 0.64 160–––500 = 0.32 20–––

500 = 0.04

40 w160 W + 160 w640 W

8001,000 = 0.8 W 200

1,000 = 0.2 w

Fig. 13-9c

Gametes reflectallele frequenciesof parental gene pool

W eggp = 0.8

Sperm

w eggq = 0.2

W spermp = 0.8

Eggs

Allele frequencies

Genotype frequencies

Next generation:

w spermq = 0.8

WWp2 = 0.64

wwq2 = 0.04

wWqp = 0.16

Wwpq = 0.16

0.64 WW 0.32 Ww 0.04 ww

0.8 W 0.2 w

Fig. 13-11a-1

Originalpopulation

Fig. 13-11a-2

Originalpopulation

Bottleneckingevent

Fig. 13-11b

Fig. 13-14b

Fig. 13-14c

Fig. 13-16

“Right-mouthed”

“Left-mouthed”

1.0

0.5

01981’82 ’83 ’84 ’85 ’86 ’87 ’88 ’89 ’90

Sample year

Fre

qu

ency

of

“lef

t-m

ou

thed

” in

div

idu

als

Fig. 13-UN1

Observations

Heritable variationsin individuals

Overproductionof offspring

Over time, favorable traitsaccumulate in the population

Individuals well-suited to theenvironment tend to leavemore offspring

Inferences

Fig. 13-13

Originalpopulation

Fre

qu

ency

of

ind

ivid

ual

sOriginalpopulation

Evolvedpopulation

Phenotypes (fur color)

Stabilizing selection Directional selection Disruptive selection

Fig. 13-UN3

Originalpopulation

Pressure ofnatural selection

Evolvedpopulation

Stabilizing selection Directional selection Disruptive selection

Fig. 13-UN5