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Chapter 15.2 Evolution

NWRC

BIO 30

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Support for Evolution

Biological evolution, simply put, is descentwith modification. This definitionencompasses small-scale evolution

(changes in gene frequency in apopulation from one generation to thenext) and large-scale evolution (thedescent of different species from a

common ancestor over manygenerations). Evolution helps us tounderstand the history of life

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Descent with Modification

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Support for Evolution

Through the process

of descent with

modification, the

common ancestor oflife on Earth gave rise

to the fantastic

diversity that we see

documented in thefossil record and

around us today.

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Support forEvolution Fossil Record Fossils are traces of organisms

that lived in the past. Whenfossils are found, they areanalyzed to determine the ageof the fossil. The absolute age ofthe fossil can be determined

though radiometric dating anddetermining the layer of rock inwhich the fossil was found.Older layers are found deeperwithin the earth than newerlayers.

Before going on watch thevideo: Evolution Primer #3: HowDo We Know EvolutionHappens?

http://uk.youtube.com/watch?v=ewtw_nZUIDQ&feature=relatedhttp://uk.youtube.com/watch?v=ewtw_nZUIDQ&feature=related

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Fossil Record

Ancestral characteristic

An ancestral characteristicis a modified

character shared between two groups and

present in their common ancestor(s) in an

unmodified form.

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Fossil Record

An example in which the ancestral

characteristicis considered is with bird

feathers and mammalian hair, both of

which are modifications on the reptilianscale. In this case the reptilian scale is

considered to be the ancestral

characteristic.

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Fossil Record

Derived characteristics

A derived characteristicis a novel modification of

the ancestral form. So, in the Last example,

both hair and feathers represent derivedcharacteristics.

The sharing of presumptive derived

characteristics is considered to be important

evidence of evolutionary relatedness.

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Comparative Anatomy

Comparative anatomy

is the study of

similarities and

differences in theanatomy of

organisms.

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Comparative Anatomy

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Comparative Anatomy

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Homologous Structures

Comparing the structures of the forelimbs

of the animals on the previous slides

(including humans) all evolved from a

common ancestor and they all sharecommon anatomical traits. Though the

limbs look strikingly different on the

outside and though they vary in function,they are very similar in skeletal structure.

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Homologous Structures

More significantly, they are derived from

the same structures in the embryo.

Structures that are embryologically similar,

but have different functions, are calledhomologous structures. Though these

animals look different, a comparison of

homologous structures indicates that theyare quite similar. This suggests that these

animals evolved from a common ancestor.

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Vestigial Organs

Some organisms have structures or organs that

seem to serve no useful function. For example,

humans have a tailbone at the end of the spinethat is of no apparent use. Some snakes have

tiny pelvic bones and limb bones, and some

cave-dwelling salamanders have eyes even

though members of the species are completelyblind.

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Vestigial Organs

Pythons and boa

constrictors have

tiny hind leg bonesburied in muscles

toward their tail ends.

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Vestigial Organs

Cave-dwelling tetra

fish (Astyanax

mexicanus) are blind;they have small

vestigial eyes that do

not work.

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Vestigial Organs

Pelvic bones in

the baleenwhale provideevidence forevolution as wecan see thatstructureschange overtime

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Vestigial Organs

Human Vestigeserector pili (muscles

that cause goose

bumps), body hair,

coccyx (tail bone),wisdom teeth,

appendix

Humans also havevestigial features,evidence of our own

evolutionary history.The appendix, forinstance, is believedto be a remnant of a

larger, plant-digestingstructure found in ourancestors.

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Analogous Structures

Two structures in biologyare said to be analogousif they perform the sameor similar function by a

similar mechanism butevolved separately.

The wings of pterosaurs(1), bats (2) and birds (3)are analogous: they serve

the same function andare similar in structure,but each evolvedindependently.

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Analogous Structures

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Comparative Biochemistry

This is the comparison of organisms at a

chemical level. For example if you

compared 2 animals very closely related

you would find more similarities in thesequences of amino acids. For example

as primates we are closely related to

chimpanzees 98.2% similar, we are 97.7%similar to gorillas and 96.3% similar to

orangutans. **glencoe

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Adaptation

Organisms that are adapted to theirenvironment are able to:

Obtain air, water, food and nutrients.

Cope with physical conditions such astemperature, light and heat.

Defend themselves from their naturalenemies.

Reproduce.

Respond to changes around them.

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Adaptation

Adaptations enable living organisms to

cope with environmental stresses and

pressures. Adaptation can be structural or

behavioral.

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Adaptation

Structural adaptations

are special body parts

of an organism that

help it to survive in itsnatural habitat (e.g.,

skin color, shape,

body covering).

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Adaptation

Behavioral

adaptations are

special ways aparticular

organism

behaves tosurvive in its

natural habitat.

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Camouflage

The outward coloration

that allows animals to

appear similar to the

plants and places in

which they live is known

as camouflage.

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Camouflage permits

predators hide in

order to ambush prey

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Or it can allow prey to

hide from predators

Either way its an

adaptive measure tosuccess in survival

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Mimicry

Mimicry is a phenomenon in which amimic bears a resemblance to another

species.. This occurs in both predatory and

prey species.

The use of mimicry is prevalent throughout nature

and is a prime example of evolution by natural

selection. Butterflies use it as a protection

mechanism in their larva stage and in the finaladult stage. Either to trick predators into thinking

they are an inedible species or perhaps an

entirely different organism all together.

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Examples of Mimicry

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Mimicry

When this moth is

threatened it pulls

back its upper wing

revealing these"Eyes" which startle

the attacker long

enough for the moth

to escape.

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Note the Eyes on the toad

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Mimicry

The venomous Coral

snake looks much like

the non-venomous

Scarlet King.

s a ca erp ar e onarcB tt fl t Milk d ith

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pButterfly eats Milkweeds with

produce a toxin. But the Monarch

has developed a way to counter

these toxins and stores them up

in its body. As an adult Monarchstaste bad and birds learn not to

eat butterflies that have black and

orange wings

The Viceroy Butterfly tastes great(to birds) but the birds who have

learned that butterflies with black

and orange wings (Monarchs)

taste bad won't eat Viceroys. The

Viceroy is the mimic

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End of Sec 15-2

Assessment Questions

1. Fossils reveal

similarities between

extinct and living

organisms and someforms have features

which link the 2

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End of Sec 15-2

Assessment Questions

2. Those features

indicate shared

ancestry and greater

fitness to theenvironment

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End of Sec 15-2

Assessment Questions

3. Complex

biochemicals found in

diverse creatures

would not haveevolved

independently and

therefore indicate

shared ancestry

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End of Sec 15-2

Assessment Questions

4. Morphological

evidence is evidence

concerning anatomy

and biochemical isevidence concerning

the DNA