Change over Time

©2008 Susan Anderson

Darwin British Naturalist Journey to Galapagos / South America Saw:

New/different SPECIES Fossils similar to living organisms

(where had these organisms gone?)

He asked why were those organisms on the islands different from those on the mainland?

Adaptations Example for Darwin:

Finches Different beaks Different foods Less competition

Evolution Gradual change over time to become

better adapted to their environment. Gradualism Punctuated Equilibria

Natural Selection “Survival of the Fittest” Extinction Overproduction – not all offspring survive Competition- usually indirect (food, space) Variations – genetic Selection- helpful variations accumulate,

unfavorable ones disappear

Formation of New Species Sometimes a group is separated from the

rest of its species. (river, mountain range, weather carries them)

If a group is separated long enough, they may evolve different traits.

“Geographic Isolation”

Continental Drift Large scale geographic isolation. Members were separated when the

continents split. Example:

Animals isolated on Australia are unlike other mammals.

Review What is evolution? Name something Darwin observed that he

thought was the result of evolution Some insects look just like sticks. How

could this be an advantage to the insects? How could the “stick trait” have evolved

through natural selection?

Fossil Record Sedimentary Rock

Most fossils are found in this type of rock Why?

Petrified Minerals dissolved in the water around remains soaks in

and replaces the remains, changing them to rocks Molds/Casts

Remains get dissolved and leave behind a hollow space (mold), then it’s filled with minerals (cast)

Preserved Can be found in tar or amber

Dating Fossils Relative Dating

Only be used when the rock layers have been preserved in their original sequence

Doesn’t tell actual age, only which fossils are older or younger

Absolute Dating Uses radioactive elements to determine exact

age of fossils HALF LIFE – the time it takes for half the atoms

of a sample to decay

Review Describe how fossils form in sedimentary

rock. Explain the process of absolute dating. How are gradualism and punctuated

equilibrium similar? How are gradualism and punctuated

equilibrium different?

Other Evidence Homologous Structures Embryology DNA similarities

Branching Tree Diagrams A diagram the shows how scientists think

different groups of organisms are related.

Review Name three types of evidence from

modern day organisms that scientists use to determine evolutionary relationships.

What are homologous structures? Most scientists today consider similarities

in DNA to be the best indicator of how closely two species are related. Why do you think this is the case?

Homework