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

Evolutionary change in horses

Millions of years ago

50

100

150

200

250

300

350

400

450

500

550

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

Equus

HyracotheriumMesohippus

Merychippus

Nannippus

Bo

dy

size

(kg

)

Evolution of birds

Smithsonian Museum, Washington, DC

• Archaeopteryx– lived about 150 mya

– links reptiles & birds

?

?

?

?

Land Mammal

Whales, you ask...

A transitional fossil linking past and present

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

tendrils

succulent 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 areanalogous 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 notLaMarck’s loss from “disuse”!

Vestigial organs

• Hind leg bones on whale fossils

Why would whaleshave pelvis & leg bonesif 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

cle

oti

de

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

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 evolutionaryrelationships?

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

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 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.