What do the following What do the following images have in common?images have in common?

What do the following What do the following images have in common?images have in common?

And how do they support And how do they support Darwin’s Theory of Evolution?Darwin’s Theory of Evolution?

The answer lies withinThe answer lies within

They all have five limbsThey all have five limbs

They all have five limbsThey all have five limbs

Or, more correctly, the bones Or, more correctly, the bones for 5 limbsfor 5 limbs

This is called a This is called a pentadactyl limbpentadactyl limb

(Pent = 5)(Pent = 5)

Scientists look for related Scientists look for related features in unrelated (or features in unrelated (or

any) organismsany) organisms

Scientists look for related Scientists look for related features in unrelated (or features in unrelated (or

any) organismsany) organisms

In order to deduce In order to deduce common ancestorscommon ancestors

And so work outAnd so work outevolutionary evolutionary relationshipsrelationships

There is one HUGE There is one HUGE problem thoughproblem though

Is the common feature Is the common feature from a common ancestorfrom a common ancestor

Is the common feature Is the common feature from a common ancestorfrom a common ancestor

Or due toOr due to Natural Natural SelectionSelection

Common features from a Common features from a common ancestorcommon ancestor

Common features from a Common features from a common ancestorcommon ancestor

Are called Are called homologoushomologous featuresfeatures

Common features due to Common features due to Natural selectionNatural selection

Common features due to Common features due to Natural selectionNatural selection

Are called Are called analogous analogous featuresfeatures

How do we tell which How do we tell which features are which???features are which???

How do we tell which How do we tell which features are which???features are which???

We We cannot !cannot !

So scientists try to choose So scientists try to choose features that do not confer features that do not confer an evolutionary advantagean evolutionary advantage

So scientists try to choose So scientists try to choose features that do not confer features that do not confer an evolutionary advantagean evolutionary advantage

Colour or camouflage Colour or camouflage would be a would be a badbad

exampleexample

So scientists try to choose So scientists try to choose features that do not confer features that do not confer an evolutionary advantagean evolutionary advantage

Bone structure is a Bone structure is a betterbetter example example

The following are all The following are all thought to have evolved thought to have evolved from a common ancestorfrom a common ancestor

The following are all The following are all thought to have evolved thought to have evolved from a common ancestorfrom a common ancestor

As they all have exactly As they all have exactly the same bone the same bone

structures and number structures and number of each boneof each bone

Even though the sizes of Even though the sizes of the bones have changedthe bones have changed

Even though the sizes of Even though the sizes of the bones have changedthe bones have changed

This is thought to have This is thought to have been due to been due to Natural Natural

selectionselection

Some scientists still argue Some scientists still argue over the value of this workover the value of this work

As we cannot prove the As we cannot prove the differences are due to a differences are due to a

common ancestorcommon ancestor

As we cannot prove the As we cannot prove the differences are due to a differences are due to a

common ancestorcommon ancestor

And are not just due to And are not just due to Natural selectionNatural selection

Comparative anatomy is Comparative anatomy is simply another jigsaw piece simply another jigsaw piece

in the puzzlein the puzzle

Comparative anatomy is Comparative anatomy is simply another jigsaw piece simply another jigsaw piece

in the puzzlein the puzzle

That isThat is

EvolutionEvolution

Scientists also noticed that Scientists also noticed that embryosembryos all share a all share a common pattern of common pattern of

developmentdevelopment

The similarities of The similarities of embryo’sembryo’sat different stages of at different stages of

development is also used to development is also used to deduce evolutionary deduce evolutionary

patternspatterns

The longer theThe longer theembryosembryos

stay similarstay similar

The more The more recentlyrecently scientists think they scientists think they

were relatedwere related

The longer theThe longer theembryosembryos

stay similarstay similar

Looking at a more Looking at a more detailed exampledetailed example

This image suggests fish This image suggests fish and salamanders are and salamanders are related to each otherrelated to each other

And tortoise and And tortoise and chickens are relatedchickens are related

And pig, cow, rabbit and And pig, cow, rabbit and human are closely relatedhuman are closely related

These evolutionary These evolutionary relationshipsrelationships

These evolutionary These evolutionary relationshipsrelationshipsShould be more Should be more

correctly stated ascorrectly stated as““More”More”

closely relatedclosely related

And they support other And they support other pieces of evidence we have pieces of evidence we have

collectedcollected

And they support other And they support other pieces of evidence we have pieces of evidence we have

collectedcollected

On the sequence of On the sequence of evolution on our planetevolution on our planet

Bibliography (5 Feb 2007)Bibliography (5 Feb 2007)

Most images from images from Most images from images from www.schoolhousevideo.orgwww.schoolhousevideo.org

Hoof image from Hoof image from http://www.horsemanpro.com/images3/Hoof%20Parallels/club2.jpghttp://www.horsemanpro.com/images3/Hoof%20Parallels/club2.jpg

Hand from Hand from http://www.simreal.com/twiki2/bin/view.pl/Simreal/handofsomeonehttp://www.simreal.com/twiki2/bin/view.pl/Simreal/handofsomeone