Changes over Time Chapter 7 Section 1. Darwin’s Theory In 1831 Charles Darwin left England on a research vessel that traveled to South America. His job.

Changes over Time

Chapter 7

Section 1

Darwin’s Theory

• In 1831 Charles Darwin left England on a research vessel that traveled to South America.

• His job was to learn about the living things he saw.

• Darwin was amazed at all the diversity he saw in Brazil.

• He also found fossil bones of animals that had died long ago.

• He started noticing that the fossil he found looked different than the living animals he was studying.

The Galapagos Islands• Darwin noticed that the plants and animals

found on the Galapagos Islands were not like the ones he found in South America.

• Darwin figured that these species came from the mainland during a storm and adapted to their new environment over time.

• For example he noticed that the Finch on Galapagos looked just like the one in South America but it had a different beak shape.

• He concluded that the beak must have changed in order to help it survive and reproduce in this new environment. This is called evolution.

Natural Selection

• States that individuals that are better adapted to their environment are more likely to survive and reproduce.

• While unfavorable traits may disappear.

3 things that affect natural selection

• Overpopulation- Most species produce more offspring than can live. Only the strongest, fastest, smartest lives.

• Competition-like the above. Resources are limited so you must be quick to survive.

• Variation- slight changes or variations in phenotype or genotype can provide slight advantages that keep you alive.

Evidence of EvolutionSection 2

Forms of Evidence

• Similar Body Structure- some body structures are similar in related species.

• Similar Early Development- During development all vertebrates look the same.

• Similar DNA- Many species share similar DNA and proteins.

How Do Fossils Form?

• Fossils form when living things die and are buried by sediments.

• Some fossils are molds that form when sediment hardens.

• Some fossils form a cast which is a solid copy of the shape.

Petrified Fossils

• These are dead organisms that have hardened into stone made of minerals.

Trace Fossils

• Bits and pieces of an organism leave behind trace fossils. It could be a footprint, or burrow.

Preserved Remains

• Sometimes organisms are preserved in full form with little or no change.

• For example insects may become trapped in tree sap and preserved for millions of years. Remember “Jurassic Park”.

Learning From Fossils

• The fossil record provides evidence about past life and past environments.

• Scientists use fossils to study how fast evolution has occurred.

Gradualism

• This is the theory that evolution occurs slowly but at a constant pace.

• If this is correct the fossil record should show intermediate forms of an organism but it doesn’t, why not?

• Answer: We haven’t found all the fossils yet and fossils are rare.

Punctuated Equilibria

• This is the theory that species evolve quickly during a short time then go through long periods of time where they don’t change much at all.

Today

• Most scientists think that evolution can occur gradually at some times and more rapidly at others.

Evolution of Species

Section 3

A Variety of Species

• Over millions of years different species have adapted to live in different habitats.

• A habitat is a specific environment that gives organisms everything they need to survive.

Genetic Diversity

• Organisms in the same species do not all have the same traits (look at us).

• Many species have much variety in their “gene pool”.

• The “gene pool” is all the genetic variations in a group of species.

• Species with a lot of variations can often adapt to changes in the environment.

• Species that do not have a lot of variations have a hard time when the environment changes.

How Do New Species Form?• A new species can form when a group of

individuals remain isolated from the rest of its species for a long time.

• Rivers, canyons, and mountains can separate a small group from the rest of their species.

• Over time the small group will evolve traits that are different from the rest. Kaibab and Abert squirrels

Inferring Species Relationships

• Scientists combined evidence from DNA, protein structure, fossils, early development, and structure to determine how different species are related.

Similarities

• The closer DNA and protein structures are the more closely related the species is.

Extinction of Species

• Most species that left fossils are now extinct.

• A species is extinct if no members of that species are still alive.

Extinction Happens• Environmental changes or a new disease

can cause a species to go extinct. If a species can’t change to survive in that environment they will fade away.

• A new predator may kill so many prey animals that the prey becomes extinct.

Adapt and Survive

• Environmental change doesn’t always lead to extinction.

• Horseshoe crabs have traits that have helped them survive since before the dinosaurs.

Classifying Organisms

Section 4

Why Do Scientists Classify?• They use classification to organize living

things into groups so that they are easier to study.

• They believe living things in the same group have common ancestors.

The Naming System of Linnaeus

• Carolus Linnaeus was one of the first to put animals into groups.

• He gave each living thing a two-part name (genus/species) he called this system binomial nomenclature.

• This makes it easier for

scientists to communicate with each other.

Genus and Species

• The first word in an organisms name is called its genus. This is the name of the group of organisms that they are closely related to.

Species

• This is the 2nd part of their name and it describes a feature of that organism. It could be what it looks like or where it lives.

• Ex. Felis concolor (puma)

Felis – group of cats

concolor- “the same color”

Felis domesticus (house cat)

Felis – group of cats

domesticus – “of the house”

Levels of Classification• Scientists use eight levels to classify

organisms.

• Organisms with the same classification at lower levels have more in common.

Branching Trees

Section 5

A Branching Tree Diagram• Shows possible

evolutionary relationships among organisms.

• It also shows the order in which specific characteristics may have evolved.