Evolution:

Supporting

Evidence

The following items demonstrate descent with modification, as well as common ancestry. (Darwin’s principle of common descent)

I -Fossil EvidenceI -Fossil Evidence (descent with modifications) (descent with modifications)

Horse fossils indicate changes in size,

as well as the transition from toes to hooves.

I - Fossil Evidence:I - Fossil Evidence: ContinuedContinued

These mollusk

fossils show

the development

of torsion, the

twisting of

their shells.

II -Homologous StructuresII -Homologous Structuresare fundamentally similar in their makeup, position and are fundamentally similar in their makeup, position and development, but are adapted to different functions. development, but are adapted to different functions.

Animal Forelimbs:

The Galapagos finch beaks are said to

be homologous. They originated in a

common ancestor and have adapted to

various environments.

Homologous v. Analogous What’s the Difference?

Homologous structures are features that originated in a shared ancestor. They have different mature forms, but develop from the same embryonic tissue.

They are inherited from a common ancestor.

Analogous Structures have features that have identical functions, and look somewhat alike, but they may be different in internal anatomy.

The evolved independently after their point of common ancestry, so they were not inherited from a common ancestor.

A bird’s wing and a moth’s wing are analogous. They allow the animals to fly, butThey have greatly different development and internal

structure.

Moth Wing Structure

Catoblepia berecynthia

Bird Wing Anatomy

Bones & Feathers

Also Analogous: Insect & horse legs

III -Vestigial StructuresIII -Vestigial Structureswhich may have been functional in an ancestor, are which may have been functional in an ancestor, are

functionless and underdeveloped in later generationsfunctionless and underdeveloped in later generations Human tailbone (coccyx)

Human Appendix

III - Vestigial Structures: III - Vestigial Structures: Structures that are vestigial in one organism, may be Structures that are vestigial in one organism, may be

functional in others.functional in others.

Nictitating membrane

Ear muscles

III - Vestigial Structures III - Vestigial Structures (continued):(continued):

Limb bones in snakes

Pelvic bones in whales

III – Vestigial Structures:III – Vestigial Structures:ContinuedContinued

• Erector pili muscleswhich cause “goose bumps”in humans

• Human baby born with fleshy tail

Does the tail really exist?

• Baby girl

born in a hospital

in Chile

IV -Embryological Similarities

Various embryos in early stages showevidence of gills slits and tails.

V - Biochemical EvidenceV - Biochemical EvidenceAll organisms have DNA (& RNA)

All organisms have ATP

Similarities in cell respiration enzymes

V- Biochemical EvidenceV- Biochemical Evidence(Continued)(Continued)

All organisms have cytochrome c

in the electron transport chain

(The difference in A.A.s is proportional to the length of time that has passed since the two shared a common ancestor.)

VI – Homeotic GenesHomeotic genes (Hox genes): regulatory genes that

determine where certain anatomical structures, such as appendages will develop in an embryo. “They seem to be master genes of development that determine the overall body organization.”

Common ancestry is demonstrated because animals share many of these Hox genes, which may control the development of similar regions.

In Summary Scientists have continued to observe examples of

common ancestry and descent with modifications

since Darwin observed finches on the Galapagos Islands so many years ago.