changes over time chapter 7 section 1. darwin’s theory in 1831 charles darwin left england on a...
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Changes over Time
Chapter 7
Section 1
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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.
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• 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.
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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.
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• 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.
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Natural Selection
• States that individuals that are better adapted to their environment are more likely to survive and reproduce.
• While unfavorable traits may disappear.
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3 things that affect natural selection
• Overpopulation- Most species produce more offspring than can live. Only the strongest, fastest, smartest lives.
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• Competition-like the above. Resources are limited so you must be quick to survive.
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• Variation- slight changes or variations in phenotype or genotype can provide slight advantages that keep you alive.
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Evidence of EvolutionSection 2
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Forms of Evidence
• Similar Body Structure- some body structures are similar in related species.
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• Similar Early Development- During development all vertebrates look the same.
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• Similar DNA- Many species share similar DNA and proteins.
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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.
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Petrified Fossils
• These are dead organisms that have hardened into stone made of minerals.
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Trace Fossils
• Bits and pieces of an organism leave behind trace fossils. It could be a footprint, or burrow.
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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”.
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Learning From Fossils
• The fossil record provides evidence about past life and past environments.
• Scientists use fossils to study how fast evolution has occurred.
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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.
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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.
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Today
• Most scientists think that evolution can occur gradually at some times and more rapidly at others.
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Evolution of Species
Section 3
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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.
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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.
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• 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.
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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
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Inferring Species Relationships
• Scientists combined evidence from DNA, protein structure, fossils, early development, and structure to determine how different species are related.
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Similarities
• The closer DNA and protein structures are the more closely related the species is.
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Extinction of Species
• Most species that left fossils are now extinct.
• A species is extinct if no members of that species are still alive.
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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.
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• A new predator may kill so many prey animals that the prey becomes extinct.
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Adapt and Survive
• Environmental change doesn’t always lead to extinction.
• Horseshoe crabs have traits that have helped them survive since before the dinosaurs.
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Classifying Organisms
Section 4
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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.
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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.
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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.
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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”
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Levels of Classification• Scientists use eight levels to classify
organisms.
• Organisms with the same classification at lower levels have more in common.
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Branching Trees
Section 5
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A Branching Tree Diagram• Shows possible
evolutionary relationships among organisms.
• It also shows the order in which specific characteristics may have evolved.