Evidence of Evolutionby Natural Selection

(Ch. 22)

Dodo bird

Evidence supporting evolution• Fossil record• Anatomical record• Molecular record• Artificial selection

Fossil record• Layers of sedimentary rock contain fossils

– new layers cover older ones, creating a record over time

– 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

Support (proof?) for a VERY old Earth.

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

The Geologic Record

Evolutionary change in horses

Millions of years ago

50

100

150

200250

300

350

400

450

500

550

60 55 50 45 40 35 30 25 20 15 10 5 0

Equus

HyracotheriumMesohippus

Merychippus

Nannippus

Bod

y si

ze (k

g)

Evolution of birds

Smithsonian Museum, Washington, DC

• Archaeopteryx– lived about 150 mya– links reptiles & birds

??

??Where are the

transitional

fossils?

Land Mammal

Whales, you ask...

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

Anatomical record• Homologous structures

– similarities in characteristics resulting from common ancestry

Homologous structures• Similar structure• Similar development• Different functions • Evidence of close

evolutionary relationship– recent common ancestor

spines

tendrilssucculent leaves

colored leaves

Homologous structures

leaves

needles

Analogous structures Separate evolution of structures

similar functions similar external form different internal structure & development different origin no evolutionary relationship

Solving a similar problem with a similar solution

Don’t be fooledby their looks!

Convergent evolution• Flight evolved in 3 separate animal groups

– analogous structures

Does this mean they have a

recent common ancestor?

Convergent evolution of analogous burrowing characteristics

Convergent evolution Fish: aquatic vertebrates Dolphins: aquatic mammals

similar adaptations to life in the sea

not closely related

Those fins & tails & sleek bodies are

analogous structures!

Parallel Evolution• Convergent evolution in common niches

– Similar ecological roles in similar environments, Similar adaptations were selected

– but are not closely related

marsupial mammals

placental mammals

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 little or no function

– 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

This is not LaMarck’s loss from “disuse”!

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

Nuc

leot

ide

subs

titut

ions

• 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

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

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 “breeds” & “varieties”

“descendants” of the wolf“descendants” of wild mustard

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

cent

of H

IV re

sist

ant t

o 3T

C

Weeks

Evolution MisconceptionsA Brief Discussion

“if we came from apes how come were not hairy and have a big mouth and did we end up looking like we do know and besides there isnt any serious proof of apes they showd a video saying an ape waswondering around in the forest that thing looked exactly like a costume that i had saw at a store know one ever cought an ape”

-From a post on the Internet

NOT THIS KIND!!!(beyond help)

The Complexity Fallacy

Don’t Get Lazy!This Isn’t How It

Happens!!!

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.

Unintelligent Design

Serial circulation in the mammalian heart

"Nothing in biology makes sense except

in the light of evolution."

-- Theodosius DobzhanskyMarch 1973

Geneticist, Columbia University(1900-1975)

-- Ernst Mayr What Evolution Is

2001Professor Emeritus, Evolutionary Biology

Harvard University(1904-2005)

Evolution is "so overwhelmingly established that it has become

irrational to call it a theory."

I might be dead, but Perhaps you children

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

music?!?

Don’t BeUnintelligent...

Ask Questions!!

Evidence of Evolutionby Natural SelectionTestable Hypotheses

(Ch. 22- 24)

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) 46

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

CentromereTelomere

Ancestral Chromosomes Fusion Homo sapiens

Inactivated centromere

Telomere sequences

Chromosome Number in the Great Apes

(Hominidae)

orangutan (Pogo) 48gorilla (Gorilla) 48chimpanzee (Pan) 48human (Homo) 46Testable!

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.”

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

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

2007-2008

Any Questions??

Review Questions

1. A complete fossil record1. Exists because of the great preservation in

ocean sediment2. Exists because of the solidification of minerals

around organisms3. Is available because of the small location in

which all organisms used to live4. Exists because organisms that die become

embedded in the soil to form rocks5. Does not exist.

2. The similarity of insect wings and bird wings is an example ofA. Behavioral adaptationsB. Geographic isolationC. Adaptive radiationD. Convergent evolutionE. Divergent evolution

3. The human appendix is an example of1. A balanced polymorphism2. Divergent evolution3. Convergent evolution4. A vestigial structure5. A homologous structure

4. One piece of evidence that supports evolution from molecular biology is:1. Carbohydrate structure2. Amino acid sequences3. Lipid composition4. Nucleotide structure5. Cellulose chains