AP Biology2006-2007

Chapter 19:MacroEvolution and the Evidence

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Macro-evolution Looking at the big picture. Looking at what drives the diversity

and unity of life

cells

DNA

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Anatomical evidence

One form of evidence in the unity of life…..

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Science sees structural similarities as evidence that organisms evolved from a common ancestor.

Structural features with a common evolutionary origin are called homologous structures.

Homologous parts are similar in structure, but

may be very different in

specific function.

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The body parts of organisms that do not have a close evolutionary origin but are similar in function are called

analogous structures.

Analogous parts are very different in

structure, but perform similar

functions.

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Vestigial organs

Why would whaleshave pelvis & leg bones

if they were alwayssea creatures?

These areremnants of

structures that werefunctional in

ancestral species

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These are structures that used to have a function, but no longer do….therefore

suggesting evolution based on new behaviors or environments Video clip

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Embryology is the study of organisms in embryonic stages.

The embryo is one of the earliest stages of growth and development of both plants and animals.

The shared features in the

embryos suggests evolution

from a distant common ancestor.

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Fish Reptile Bird Mammal

Pharyngealpouches

Pharyngealpouches

Tail Tail

Shared Common Features:• a tail posterior to the anus• spinal cord• muscles arranged in bundles• cartilage dorsal notochord (becomes the vertebral column)• Pharyngeal gill slits

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All living things have A,T,C,G in their DNA and use the same codon chart to code for the same amino

acids.

BIOCHEMISTRY

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The biochemistry (DNA) of a bat is much closer to that of a whale, than that of a

bird.Why?

The same technology used to determine paternity can be done to determine

shared ancestry.

Because bats and whales are mammals! Therefore, more closely related….. Bat Whale Bird

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Another form of evidence that evolution occurs….

Fossil record

Millions of years ago

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

Equus

HyracotheriumMesohippus

Merychippus

Nannippus

Bo

dy

size

(kg

)

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Fossils are usually formed when an organism is covered by sediments that then harden into sandstone, slate, mudstone or flint.

Most organisms do not fossilize and those that do are usually destroyed by

geological processes or they never surface for examination.

We have only discovered about 250,000 fossilized species. This tells us that there

are many gaps in the fossil record.

Most of the time, organisms die in locations that are not conducive to fossilization.

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Fossils are evidence of organisms that lived long ago that are preserved in Earth’s rocks.

TYPES OF FOSSILSFossils Types Formation

Trace fossils

Casts

Molds

Petrified fossils

Amber-Preserved

orfrozen fossils

A trace fossil is any indirect evidence

left by an animal and may include a

footprint, a trail, or a burrow.

When minerals in rocks fill a space

left by a decayed organism, they make

a replica, or cast, of the organism.

A mold forms when an organism is

buried in sediment and then decays,

leaving an empty space.

Petrified-minerals sometimes penetrate

and replace the hard parts of an organism

At times, an entire organism was

quickly trapped in ice or tree sap that

hardened into amber.

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Paleontologists, scientists who study ancient life, are like detectives who use fossils to understand events that happened long ago.

They use fossils to determine the kinds of organisms that lived during the past and sometimes to learn about their behavior.

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• Relative Dating Techniques

Law of superposition (Nicolaus Steno)

You cannot use this technique to get the actual age of a specimen

Most Primitive

Most Complex

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The first fossilized fish appear buried below the first fossilized amphibians which appear

below the first fossilized reptiles which appear below the first fossilized birds and mammals.

This is consistent with the Darwinian model of origins which says that birds and mammals evolved from earlier reptile ancestors, which

evolved from amphibian ancestors which

evolved from fish ancestors.

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Fossil evidence for evolution concerns transitional fossils.

Transitional fossils are fossils which are thought to document the evolutionary change, or transition, of one species

into another.

The Mesohippus, Merychippus, and Pliohippus are all thought to be

transitional fossils, documenting the evolution of the Eohippus into the

modern horse.

Perhaps one of the most famous “transitional fossils” of all time was the archaeopteryx

[ahr-kee-op-tuh-riks], which shows evidence of transitioning between a reptile and a bird.

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Evolution of birds

Smithsonian Museum, Washington, DC

Archaeopteryx lived about 150 mya links reptiles & birds

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Evolution of land animals 2006 Fossil Discovery

“Tiktaalik” “missing link” from sea to land animals

from swimming (0 legs) to walking (4 legs)

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????Where are the

transitional

fossils?

Land Mammal

Aquatic Mammal

At first,I was justa joke!

Evolution of marine mammals

But then,they actually

found my fossil!

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• Radiometric Dating TechniquesTo find the specific age of rocks, scientists use

radiometric dating.By using the radioactive isotopes present in rocks, and understanding the rates at which these isotopes decay, scientists can determine approximate age of the

rocks.

Atoms of the same element with differing atomic weights can be naturally found in the environment, and are called isotopes.

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Radioactive isotopes are atoms with unstable nuclei that break down, or decay, over time, giving off radiation. The isotope is eventually changed into, or replaced by another

element over time.

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As specific atoms decay they emit radiation and lose electrons, which causes them to turn into a different

element.

So- these atoms change from one thing into something else over time- and they do this at a constant rate.

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If you know what the unstable atom is (Carbon 14) and you know what it turns into as it decays (Nitrogen 14).

And you know the rate at which the unstable atom decays/turns into something else

You can measure the amount of the unstable parent atom in the rock….and compare that to the amount of the new atom

This will tell you the age of the sample rock.It takes 5,730 years for ½ of Carbon 14 to

turn into Nitrogen 14

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The half-life of a radioactive atom is the time it takes for half of that atom in a sample to decay and turn into another element.

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• The element potassium-40 decays to argon-40 and has a half-life of approximately 1.25

billion years

• The element carbon-14 decays more rapidly into Nitrogen-14, and has a half-life of only 5,730 years.

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Because Carbon 14 has such a short half-life, it can only be used to date things that died recently in geologic

history (under 70,000 years ago).

If you need to date rocky material from farther back in our geologic past, you must use another method, such as Potassium/Argon, which has

a much longer half-life.

• You can only date organic remains using carbon 14

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Some isotopes, however, decay slowly, and several of these are used as geologic clocks. The parent isotopes and corresponding daughter products most commonly used to determine the ages of ancient rocks are listed

below:

Most radioactive isotopes have rapid rates of decay (that is, short half-lives) and lose their

radioactivity within a few days or years.

Parent IsotopeStable Daughter Product

Currently Accepted Half-Life Values

Uranium-238 Lead-206 4.5 billion years

Uranium-235 Lead-207 704 million years

Thorium-232 Lead-208 14.0 billion years

Rubidium-87 Strontium-87 48.8 billion years

Potassium-40 Argon-40 1.25 billion years

Samarium-147 Neodymium-143 106 billion years

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256 14C atoms How many carbon-14 atoms and how many

nitrogen-14 atoms will this rock have in

5,730 yrs.

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After 5730 years

or 1 half-life

128 14C and

128 14N atoms

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After 11,460 yrs

or 2 half-lives

64 14C and

192 14N atoms

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After 17,190 yrs

or 3 half-lives

32 14C and

224 14N atoms

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After 22,920 yrs

or 4 half-lives

16 14C and

240 14N atoms

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After 28,650 yrs

or 5 half-lives

8 14C and

248 14N atoms

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After 34,380 yrs

or 6 half-lives

4 14C and

252 14N atoms

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After 40,110 yrs

or 7 half-lives

2 14C and

254 14N atoms