Chapter 21.

Evidence of Evolutionby Natural Selection

Dodo bird

Evolution is "so overwhelmingly established that it has become irrational to call it a theory."

-- Ernst Mayr What Evolution Is

2001Professor Emeritus, Evolutionary Biology

Harvard University

(1904-2005)

Support for Darwin’s ideas _______________

change over time ___________________

Homologous structures Analogous structures embryology

_________________ measure of common

ancestry ________________

induced evolution

Fossil Record

Comparative Anatomy

Molecular Analysis

Artificial Selection

Fossil record Layers of sedimentary rock contain fossils

new layers cover older ones, creating a record over time

fossils within layers show that a succession of organisms have populated Earth throughout a long period of time

Formation of sedimentary strata containing fossils

1 Rivers carry sediment to the ocean. Sedimentary rock layers containing fossils form on the

ocean floor.

2 Over time, new strata are deposited, containing fossils

from each time period.

3 As sea levels change and the seafloor is pushed upward, sedimentary rocks are

exposed. Erosion reveals strata and fossils.

Younger stratum with more recent

fossils

Older stratum with older fossils

 A gallery of fossil types

(a) Dinosaur bones being excavated from sandstone

(g) Tusks of a 23,000-year-old mammoth, frozen whole in Siberian ice

(e) Boy standing in a 150-million-year-old dinosaur track in Colorado

(d) Casts of ammonites, about 375 million

years old

(f) Insects preserved whole in amber

(b) Petrified tree in Arizona, about 190 million years old

(c) Leaf fossil, about 40 million years old

Fossil record Today’s organisms descended from

ancestral species Support for a very old earth

A dragonfly fossil from Brazil, more than 100 million years old

Evolution of birds

Smithsonian Museum, Washington, DC

Archaeopteryx lived about 150 mya links reptiles & birds

Evolutionary Change in Horses

??

??Where are the

Intermediates?

Land Mammal

A transitional fossil linking past and present

Oh. Here they

Are!

2006 Fossil Discovery of Early Tetrapod

Tiktaalik “missing link” from sea to land animals

Burgess Shale

Burgess Shale British Columbia 505 million years ago (Cambrian

Explosion) Period when animals rapidly diversified

in body plan/anatomical feature _________________Taphonomic window

Anatomical record

Homologous structures similarities in characteristics resulting

from _______________common ancestry

Homologous structures

Similar _________ Similar ____________ Different _________ Evidence of close

evolutionary relationship _______ common

ancestor

structure

development

functions

recent

spines

tendrilssucculent leaves

colored leaves

Homologous structures

leaves

needles

Analogous structures

Separate evolution of structures similar ____________ similar ________________ _____________ internal structure &

development different_________ no ______________________

Solving a similar problem with a similar solutionSolving a similar problem with a similar solution

Don’t be fooledby their looks!

structureexternal form

different

origin

evolutionary relationship

Analogous structures 3 groups with wings

does this mean they have a recent common ancestor?

flight evolved 3 separate times = evolving similar solutions to similar “problems”

flight evolved 3 separate times = evolving similar solutions to similar “problems”

Convergent evolution Fish: aquatic vertebrates Dolphins: aquatic mammals

similar adaptations to life in ______ environments

not closely related

Those fins & tails & sleek bodies are

analogous structures!

similar

Parallel Evolution Convergent evolution in common niches

Similar ecological roles in ________environments, Similar adaptations were selected

but are not closely related

marsupial mammalsmarsupial mammals

placental mammalsplacental mammals

different

Convergent evolution of analogous burrowing characteristics

marsupial mole

placental mole

Parallel types across continentsNiche Placental Mammals Australian Marsupials

BurrowerMole

Anteater

Mouse

Lemur

Flyingsquirrel

Ocelot

Wolf Tasmanian “wolf”

Tasmanian cat

Sugar glider

Spotted cuscus

Numbat

Marsupial mole

Marsupial mouse

Anteater

Nocturnalinsectivore

Climber

Glider

Stalkingpredator

Chasingpredator

Vestigial organs Structures that serve _________________

remnants of structures that were functional in ancestral species

deleterious mutations accumulate in genes for non-critical structures without reducing fitness snakes & whales — remains of pelvis & leg

bones of walking ancestors eyes on blind cave fish human tail bone

little or no functions

Vestigial organs Hind leg bones on whale fossils

Why would whaleshave pelvis & leg bones

if they were alwayssea creatures?

Comparative embryology Similar embryological development in

closely related species all vertebrate embryos have similar

structures at different stages of development gill pouch in fish, frog, snake, birds, human, etc.

Anatomical similarities in vertebrate embryos

Pharyngealpouches

Post-analtail

Chick embryo Human embryo

Molecular record

0 25 50 75 100 1250

25

50

75

100

Millions of years ago

Horse/donkey

Sheep/goat

Goat/cow

Llama/cow

Pig/cow

Rabbit/rodent

Horse/cow

Human/rodent

Dog/cow

Human/cow

Human/kangaroo

Nu

cleo

tid

e su

bst

itu

tio

ns

Comparing DNA & protein structure universal genetic code!

DNA & RNA compare common genes

cytochrome C (respiration) hemoglobin (gas exchange)

Closely related species have sequences that are more similar than distantly related species A molecular record of evolutionary

relationships

Closely related species have sequences that are more similar than distantly related species A molecular record of evolutionary

relationships

Why comparethese genes?

Comparison of a protein found in diverse vertebrates

Species

Human

Rhesus monkey

Mouse

Chicken

Frog

Lamprey14%

54%

69%

87%

95%

100%

Percent of Amino Acids That AreIdentical to the Amino Acids in aHuman Hemoglobin Polypeptide

Comparative hemoglobin structure

Number of amino acid differences betweenhemoglobin (146 aa) of vertebrate species and that of humans

Number of amino acid differences betweenhemoglobin (146 aa) of vertebrate species and that of humans

100 20 30 40 50 60 70 80 90 100 110 120

LampreyFrogBirdDogMacaqueHuman

328 45 67 125

Why does comparingamino acid sequencemeasure evolutionary

relationships?

Building “family” treesClosely related species (branches) share same line of descent until their divergence from a common ancestor

Artificial selection Artificial breeding can use variations in

populations to create vastly different “________” & “__________”

“descendants” of the wolf

“descendants” of wild mustard

breeds varieties

It’s Important To Remember How Powerful And Fast Selection Can Be!!!

Natural selection in action

Insecticide & drug resistance insecticide doesn’t

kill all individuals resistant survivors

reproduce resistance is inherited insecticide becomes

less & less effective

Evolution of drug resistance in HIV

PatientNo. 1

Patient No. 2

Patient No. 3

Per

cen

t of

HIV

res

ista

nt

to 3

TC

Weeks

Evolution Misconceptions

Evolution is not goal-orientedAn evolutionary trend does not mean that evolution is goal-oriented.

Surviving species do not represent the peak of perfection. There is compromise & random chance involved as well

Remember that for humans as well!

Evolution is not the survival of the fittest.

Rather it is the survival of the just

good enough.

"Nothing in biology makes sense except in the light of evolution."

-- Theodosius DobzhanskyMarch 1973

Geneticist, Columbia University

(1900-1975)

I might be dead, but Perhaps you children

would appreciate a bit of what you call the “rap”

music?!?

Just Because Things Seem Obvious

Doesn’t Mean They Don’t Need To Be Supported

Peppered Moths Dark vs. light variants

Year % dark % light1848 5 951895 98 21995 19 81

Peppered moth What was the selection factor?

early 1800s = pre-industrial England low pollution lichen growing on trees = light colored bark

late 1800s = industrial England factories = soot coated trees killed lichen = dark colored bark

mid 1900s = pollution controls clean air laws return of lichen = light colored bark

industrial melanism

Genome sequencing What can whole genome

sequence data tell us about evolution of humans?

Primate Common Ancestry?Chromosome Number in

the Great Apes (Hominidae)

orangutan (Pogo) 48gorilla (Gorilla) 48chimpanzee (Pan) 48human (Homo) 4646

Chromosome Number in the Great Apes

(Hominidae)

orangutan (Pogo) 48gorilla (Gorilla) 48chimpanzee (Pan) 48human (Homo) 4646

Hypothesis:Hypothesis:Change in chromosome number?Change in chromosome number? If these organisms share a common ancestor, then is there evidence in the genome for this change in chromosome number

Hypothesis:Hypothesis:Change in chromosome number?Change in chromosome number? If these organisms share a common ancestor, then is there evidence in the genome for this change in chromosome number

Could we have just lost a pair ofchromosomes?

Chromosomal fusionTestable prediction:Testable prediction: If common ancestor had 48 chromosomes (24 pairs),then humans carry a fused chromosome (23 pairs).

Testable prediction:Testable prediction: If common ancestor had 48 chromosomes (24 pairs),then humans carry a fused chromosome (23 pairs).

Centromere

Telomere

Ancestral Chromosomes Fusion Homo sapiens

Inactivated centromere

Telomere sequences

Chromosome Number in the Great Apes

(Hominidae)

orangutan (Pogo) 48gorilla (Gorilla) 48chimpanzee (Pan) 48human (Homo) 4646

Chromosome Number in the Great Apes

(Hominidae)

orangutan (Pogo) 48gorilla (Gorilla) 48chimpanzee (Pan) 48human (Homo) 4646Testable!

This is what makes evolution science

& not belief!

Test of the Human Genome“Chromosome 2 is unique to the human lineage of evolution, having emerged as a result of head-to-head fusion of two chromosomes that remained separate in other primates. The precise fusion site has been located in 2q13–2q14.1, where our analysis confirmed the presence of multiple subtelomeric duplications to chromosomes 1, 5, 8, 9, 10, 12, 19, 21 and 22. During the formation of human chromosome 2, one of the two centromeres became inactivated (2q21, which corresponds to the centromere from chimp chromosome 13) and the centromeric structure quickly deterioriated.”

“Chromosome 2 is unique to the human lineage of evolution, having emerged as a result of head-to-head fusion of two chromosomes that remained separate in other primates. The precise fusion site has been located in 2q13–2q14.1, where our analysis confirmed the presence of multiple subtelomeric duplications to chromosomes 1, 5, 8, 9, 10, 12, 19, 21 and 22. During the formation of human chromosome 2, one of the two centromeres became inactivated (2q21, which corresponds to the centromere from chimp chromosome 13) and the centromeric structure quickly deterioriated.”

Hillier et al (2005) “Generation and Annotation of the DNA sequences of human chromosomes 2 and 4,” Nature 434: 724 – 731.

Chr 2

Ancestral Chromosomes Fusion Homo sapiens

Inactivated centromere

Telomere sequences

Human Chromosome #2 shows the exact point at which this fusion took place

Human Chromosome #2 shows the exact point at which this fusion took place

Well I’llbe a monkey’s…or an ape’s…

uncle!

Geographic variation in chromosomal mutations

1 2.4 3.14 5.18 6 7.15

XX1913.1710.169.128.11

1 2.19 3.8 4.16 5.14 6.7

XX15.1813.1711.129.10

Unity & Diversity Only evolution explains both the unity

& diversity of life By attributing the diversity of life to

natural causes rather than to supernatural creation, Darwin gave biology a strong, scientific, testablefoundation

2007-2008

Any Questions??

1. A complete fossil record

A. Exists because of the great preservation in ocean sediment

B. Exists because of the solidification of minerals around organisms

C. Is available because of the small location in which all organisms used to live

D. Exists because organisms that die become embedded in the soil to form rocks

E. Does not exist

2. The similarity of insect wings and bird wings is an example of

A. Behavioral adaptations

B. Geographic isolation

C. Adaptive radiation

D. Convergent evolution

E. Divergent evolution

3. The human appendix is an example of

A. A balanced polymorphism

B. Divergent evolution

C. Convergent evolution

D. A vestigial structure

E. A homologous structure

One piece of evidence that supports evolution from molecular biology is:

A. carbohydrate structure

B. amino acid sequence

C. lipid composition

D. nucleotide structure

E. cellulose chains

Any Questions??