Chapter 7

Changes Over Time

Who is Charles Darwin?

• Naturalist who traveled the world in the 1830’s

• Observed similarities and differences between species in South America and the Galapagos Islands

• Wrote a book called “The Origin of Species”

• Formed the theory of evolution through natural selection.

What is Evolution?As a WORD• A gradual change

in a species over time.

• Most people agree with this idea.

As a THEORY

• All species have evolved from a common ancestor.

• There is a lot of controversy over this idea.

What Words to Know?

• Species- A group of similar organisms that reproduce and create offspring that can reproduce.

• Adaptation- A trait that helps an organism survive in its environment.

• Natural Selection- A process where individuals from a species are better adapted to their environment, and survive longer to reproduce and pass on their good genes.

http://www.sciencenetlinks.com/interactives/evolution.html

How does Natural Selection Work?

Most species produce more offspring than can possibly survive

Food and resources are limited, so offspring compete to survive

Offspring have variations that make some better

adapted to their environment

Offspring that are better adapted, survive and reproduce, thus

passing on their genes to the next generation

What leads to Natural Selection?

• Overproduction- producing far more offspring than can possibly survive.

• Competition- Limited resources (food, space, etc.)

• Variations- Differences between members of a species.

• Selection- Variations that make individuals more adapted to environment (helpful variations).

What Causes Variations?

• Mutations- Changes in genes or chromosomes.

• Only traits that are inherited or controlled by genes can create variations and be acted on by natural selection.

How do New Species Form?

• Natural disasters, rivers, canyons, mountain formations, and human disruptions can lead to isolation within a species.

• When a group of individuals

from a species remains separate

long enough, different traits evolve.

What is Geographic Isolation?

• The theory that the continents started as one large land mass or supercontinent called Pangaea.

• Over millions of years the one continent split apart isolating individual groups of the same species.

http://pubs.usgs.gov/publications/text/historical.html

How Fast does Evolution Occur?

• Two Theories

• Some scientists believe that both occur

• Gradualism and Punctuated Equilibria

What is Gradualism?• Gradualism – A theory that evolution

occurs slowly but steadily over time (Darwin agrees with this theory)

What is Punctuated Equilibria?

• Punctuated Equilibria – A theory that species evolve during short periods of rapid change

• Short bursts with long periods of stability between

• This theory explains the absence of intermediate fossils in branches of evolution

What Evidence is there for Evolution?

• The fossil findings and the fossil record (most evidence)

• Similarities in body structure (homologous structures)

• Similarities in DNA (widely used today)

What are Fossils?• A fossil is the preserved remains or traces of an

organism that lived in the past.

• A fossil can be formed from a bone, tooth, shell, or other part of an organism.

• Other fossils can be traces of the organism, such

as footprints or worm burrows left in mud that later turned to stone.

How do fossils form?• Organism gets buried in

sediment, tar pits, ice, or sap (amber).

• Form from a bone, tooth, shell, leaves, stems, roots, seeds, prints, or other parts of an organism

• Petrified Fossils= remains turn to rock

• Molds= remains dissolve and leave a hollow space.

• Cast= mold filled with minerals.

• Fossil Fuels = forests that are buried and under extreme pressure for millions of years form coal (carbon).

How Do You Determine a Fossils Age?

• Relative Dating =Date a fossil relative to other

things around itUsed to determine which of

the 2 fossils is older.

Example: Fossils found in rock layers

Not used to find actual age of fossils

• Absolute Dating =Used to determine the actual

age of a fossil.

Example: Comparing the amount of radioactive elements in rock where fossil is found to the amount of element it breaks down into.

CARBON DATING

What do Fossils Reveal?

• History of Earth, Fossil Record includes millions of collected fossils, but is incomplete.

• The structure of extinct animals, fossils are used to build models of animals.

• Clues as to how and when organisms evolved.

What are Homologous Structures?

• Similar structures that related species have inherited from a common ancestor

• Similarities provide evidence that certain organisms all evolved from a common ancestor

What is Embryonic Development?

• Looking at the changes of an organisms fetus while still in the womb

• Different embryos are compared during development, the more similarities, the more closely related

What is the Geologic Time Scale?

• A “calendar”, a timeline of Earth’s history.

• Spans more than 4.6 billion years

• Longest span of time is Precambrian, the first 4 billion years (not many fossils)

• Paleozoic, Mesozoic, and Cenozoic make up the last 0.6 billion years and are divided into eras and periods

Geologic Time Scale:

How do Scientist Show Evolutionary

Relationships?

• Branching Tree or Cladogram- a diagram that shows evolutionary relationships between different species.

Fossil Websites

http://www.bbc.co.uk/beasts/fossilfun/

http://www.rom.on.ca/quiz/fossil/

http://dsc.discovery.com/convergence/dinosaurplanet/interactive/interactive.html

• http://www.fieldmuseum.org/sue/whosue.html

• http://ology.amnh.org/paleontology/fightingdinos/index.html