THE CHANGING EARTHUnit C – Section Two – Evolution & Natural

Selection

WHAT IS EVOLUTION?http://www.youtube.com/watch?v=CKDSiNf_r

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http://www.youtube.com/watch?v=faRlFsYmkeY

THE IMPORTANCE OF FOSSILS

...What’s My Job??

PaleontologyThe study of “fossils”

Scientists have discovered approximately 250,000 fossil species.

Represents only a small number of species that can be found on earth.

PaleontologyMany organisms leave no evidence of their

existence in the fossil record, thus they go unnoticed.

Fossils: What Can They Tell Us?1. Different species lived on Earth at various

times in the past. Few species living today were alive 1 million years ago.

2. The complexity of living organisms increases from the past to the present.Why??

3. Living species and their most closely matching fossils are usually found in the same geographic location.

Dating a FossilScientists use “Radiometric Dating” to

determine the age of a fossil.

Radioactive decay of isotopes help determine a fossil’s age.

Fossil FlawsThe geological record is not perfect!

Some layers of rock do not contain any fossils.

A “missing link” occurs when we have no transitional organisms from one geological era to the next.

“Missing Links” in HumansUntil the 20th century, there was no link

between animals and modern day humans.

Discoveries of fossils were key “transition” fossils that helped connect modern humans to other animals.

BiogeographyThe study of the geographic distribution of

life on Earth.

Attempts to answer these questions:Where do certain species live?Why do they live there?How did they end up there?

Example: Why does the Arctic have polar bears and the Antarctic have penguins?

IMPORTANCE OF ISLANDSBecause they are separated from larger

landmasses, island are of particular importance to evolutionary biology.

Islands contain a small number of species because immigration from the mainland is difficult.

Terrestrial mammals aren’t found on oceanic islands more than 300 miles from the mainland.

IMPORTANCE OF ISLANDSBut, bats are plentiful as they have a long

distance flying ability.

ENDEMIC SPECIESSpecies that are found in one location only,

typically on a remote island.Example: Hawaii, Galapogas Islands

Suggests that they evolved in isolation with little competition.

As these species are found in so few places, their numbers tend to be smaller so are considered endangered.

BLUE-FOOTED BOOBY (Endemic)Found on the Galapogas Islands

Booby is adapted from bobo, Spanish for “stupid fellow”.

Long pointed wings and a narrow pointed bill.

Show off their feet when they are courting females with an exaggerated step-walk.

http://www.youtube.com/watch?v=1NAKg46s1DA&feature=fvw

GALAPAGOS TORTOISE (Endemic)Largest tortoises on Earth, slow moving

reptiles.

Cold blooded creatures that sunbathe for several hours in the morning to absorb energy through their shells.

EVIDENCE OF EVOLUTION COMPARATIVE ANATOMY

Comparing organisms in development can give us an idea about the relationship between species.

Species that looked quite different as adults often had close similarities as developing embryos.

PAGE 144, FIGURE 2

http://www.pbs.org/teachers/connect/resources/710/preview/

Homologous StructuresFeatures with similar structures but different

functions.

Suggests that organisms share common ancestors but went through modification that led to different functions.

Can you think of any?

Homologous Structure ExampleORGANISM FORELIMBS PURPOSEBird Wings & Legs Flight MovementWhale Fins Swimming BalanceHorse Legs MovementHuman Arms & Legs Movement

ANALOGOUS STUCTURESFeatures that are similar in appearance and

in function, but appear to have different evolutionary origins.

EXAMPLES: Wings of Birds, Wings of Insects, Wings of Bats All organisms use wings for same function (to fly),

but developed differently

Analogous Structure ExampleINSECT WINGS BIRD WINGSNot Feathered FeatheredUsually 2 Pairs of Wings Usually 1 Pair of WingsNo Bones in Wings Bones are PresentSmall in Size Large in Size

VESTIGIAL FEATURESStructures that no longer serve a useful

function, they likely served a function in an ancestor organism.

They are present in all species and serve as evidence for evolution, as they provide us with information about how organisms have changed.

VESTIGIAL FEATURESStructures that no longer serve a useful

function, they likely served a function in an ancestor organism.

They are present in all species and serve as evidence for evolution, as they provide us with information about how organisms have changed.

The appendix, tail bone, and wisdom teeth all are examples of vestigial features in human beings.