Evidence of Evolution (and Natural Selection)

Evidence supporting evolution• Fossil record– shows change over time– Geographic Distribution (past and

present)• Anatomical record– comparing body structures

• homology & vestigial structures

• Molecular record– comparing protein & DNA sequences

• Artificial selection– human caused evolution

1. Fossil record• Layers of rock contain fossils – new layers cover older ones• creates a record over time

– Fossils show a series of organisms have lived on Earth • over a long period of time

– Through time, these organisms evolve into new forms

Fossils shape ideas about evolution Fossils: direct or indirect remains of organisms

preserved in media such as sedimentary rock, amber, ice, or tar

Ammonite casts–Fossilized organic matter in a leaf

–Fossilized organic matter in a leaf Ice Man”

Fossils tell a story…

What has the fossil record shown us?• The creatures alive today haven’t

always been around.– But they do resemble creatures that were present in the

past (See elephant evolution below)

Land Mammal

?

???

Where are the

intermediate

fossils?

Where are the

intermediate

fossils?

Ocean Mammal

Complete seriesof transitionalfossils

We found the fossil — no joke!

Whale Evolution- Whales originated as predatory land mammals, that evolved into Ocean Mammals

8

Ambulocetus- whale ancestor

Carl Buell

Evolution from sea to land• 2006 fossil discovery of early tetrapod– 4 limbs

• Missing link from sea to land animals

Evolution of BirdsArchaeopteryx, pictured along with other fossils that illustrate a link between birds and dinosaurs

Trilobytes… lots of diversity, resulting from heavy selective pressures and empty

niches

Geographic Distribution• Different species descended

with modification from a common ancestor- Populations in different places adapted to different environments…

• Convergent evolution-Different species living in similar environments in different parts of the world sometimes have similar structures and functions because they experienced similar pressures of natural selection-

Convergent evolution• 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”

2. Anatomical record

Animals with different structures on the surfaceAnimals with different structures on the surface

But when you look under the skin…But when you look under the skin…

It tells an evolutionary story of common ancestorsIt tells an evolutionary story of common ancestors

Compare the bones

• The same bones under the skin– limbs that perform different functions are built

from the same bones

Homologous structures• Homologous Structures- Structures that come

from the same origin (same tissues during development)

• homo- = same• -logous = information

• Forelimbs of human, cats, whales, & bats – same structure

• on the inside– same development in embryo – different functions

• on the outside– evidence of common ancestor

Evolution of Land Vertebrates

Note: homologous limb bones

Vestigial organs structure—a body structure in a present-day organism that no longer serves its original purpose, but was probably useful

to an ancestor.• Hind leg bones on whale fossils

Why would whales have pelvis & leg bones if they were always sea creatures?

Why would whales have pelvis & leg bones if they were always sea creatures?

Some Examples

Other Vestigial Organs?

• Can you Provide examples of any other vestigial organs?– Appendix– Coccyx

But don’t be fooled by these… Analogous structures-

Structures that look similar and have the same function

But: different internal structure & development

different origin no evolutionary relationship

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

Analogous structures Dolphins: aquatic mammal Fish: aquatic vertebrate

both adapted to life in the sea

not closely related

3. Molecular record

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

LampreyFrogBirdDogMacaqueHuman

328 45 67 125

• Comparing DNA & protein structure– everyone uses the same genetic code! • DNA

compare common genes compare common proteins

compare common genes compare common proteins

number of amino acids different from human hemoglobinnumber of amino acids different from human hemoglobin

Building “family” treesClosely related species are branches on the tree — coming from a common ancestorClosely related species are branches on the tree — coming from a common ancestor

• How do we know natural selection can change a population?– we can recreate a similar process– “evolution by human selection”

4. Artificial selection

“descendants” of wild mustard“descendants” of wild mustard

Selective BreedingHumans create the change over timeHumans create the change over time

“descendants” of the wolf“descendants” of the wolf

Artificial Selection gone bad!• Unexpected

consequences of artificial selection

Pesticide resistancePesticide resistance

Antibiotic resistanceAntibiotic resistance

Insecticide resistance

• Spray the field, but…– insecticide didn’t

kill all individuals• Variation in response

to the chemical

– resistant survivors reproduce

– resistance is heritable– insecticide becomes

less & less effective

Adaptations: Evidence for Evolution

• an adaptation is any variation that aids an organism’s chances of survival in its environment.

• According to Darwin’s theory, adaptations in species develop over many generations

– Because organisms have adaptation to their specific environment, each organism has become specialized.

Structural adaptations arise over time

• camouflage, an adaptation that enables species to blend with their surroundings.

• Because well-camouflaged organisms are not easily found by predators, they survive to reproduce.

Structural adaptations arise over time

• Mimicry is a structural adaptation that enables one species to resemble another species.

• Predators may learn quickly to avoid any organism with their general appearance

Convergent evolution led to mimicry• Why do these pairs look so similar?

Monarch malepoisonous

Viceroy maleedible

fly bee moth bee

Which is the fly vs. the bee?Which is the moth vs. the bee?

Physiological adaptations can develop rapidly

• In general, most structural adaptations develop over millions of years.

• However, there are some adaptations that evolve much more rapidly.

• The evolution of insecticide resistance is an example of natural selection in action

Adaptation vs Acclimation

• Adaptations are inherited trait (genetic) that increases an organism’s chance of survival. – May be anatomical, physiological, or behavioral

(instinctual) and will happen over many successive generations. • Ex. Deer growing thicker coats in the winter

• An Acclimation is a short term learned response to an environmental change.– Ex. Deer avoiding daytime browsing during hunting

season

Evolution and Adaptations• Galapagos tortoises have shell

shapes that are adapted to the vegetation of their island.

• Tortoises that live on islands that have low vegetation have domed shells so that they don’t get stuck.

• Tortoises that live on islands with high vegetation have saddle shells so that they can stretch higher for out of reach foods.

Cladograms

• shows the evolutionary development of the species.

• shows the relationships between species.• resembles a tree and its branches.

Example Cladogram

How to Interpret a Cladogram• To determine how closely related organisms are

to one another :• look for vertices or nodes– they occur at (G), (F), and (E).

• species that share the same node are more closely related to each other– (B) and (C) are the most closely related because they

share the most recent – ancestor (E).– (A), (B), (E), and (C) are also closely related through

(F).

How to Read a CladogramTo determine approximate age • examine where in the cladogram the species is found.• the bottom of the cladogram is where the most ancient

(oldest) species are Found.• as you go up the species get younger and younger.

– oldest species = (G)– youngest = (A), (B), (C), and (D).

To determine the amount of evolution in a species• look for a species that has produced a number of

new species from it.– species (F) has evolved to form 4 new species ; (A), (B),

(C), and (E).– species (D) has remained in its own lineage for many

millions of years.

Example Cladogram