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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