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Evolution Cont’d
7th Grade BiologyMr. Joanides
http://www.buildamovement.com/blog/wp-content/uploads/2009/09/evolution.jpg
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The Fossil Record
• Fossil – Preserved remains or markings left by organisms that live in the past.– Most fossils are found in sedimentary rock– Others can be buried under volcanic ash and dust
• Sedimentary rock – eroded particles of sand, silt, etc that flow down river to seas and swamps and settle at the bottom. Over time, they are cemented together under pressure and heat to form rock.
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Sedimentary Rock Being Formed
http://geoscape.nrcan.gc.ca/
nsask/images/rocks1_e.jpg
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The Fossil Record
• Provides evidence of Earth’s changing life. • Ex. Timelines from class
• Earth is 4.6 billion years old (byo)• Oldest known fossil is 3.8 byo. • Fossils of prokaryotes [bacteria and archaea]
3.5 byo (oldest form of life)• Fossils in younger rock show evidence of
evolution
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Evolution of the Whale
• Modern whales evolved 50 million years ago…• But from where?
– Fossils of extinct species can help put the puzzle together.
– Basilosaurus
http://upload.wikimedia.org/wikipedia/commons/archive/4/4e/20080706155500!Basilosaurus.jpg
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Geographic Distribution• Differences and similarities between
organisms around the world– Evolved from ancestral forms
TOPIC FOR DISCUSSION• Why do S. American tropical species have
more in common with S. American desert species than they do with African desert species?
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Australia…Unique Plants and Animals
• Numerous pouched mammals (marsupials)• Few placental mammals
• Why did this happen?
• Also…a good case study for introduced animals…economic and ecologic nuisances
http://www.camelotbears.com/images/koala_baby_pic.jpg
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Homologous Structures• Forelimbs of animals & goose bumps
http://www.thisviewoflife.org/evolution/forelimb%20homologies.jpg
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Vestigial Structures• Modern whales have no hind limbs, but still
have remnant hipbones
http://www.answersingenesis.org/home/area/magazines/tj/images/v14n2_vestigial_structures.gif
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Definitions
• Homologous structures – structural similarities species share from a common ancestor
• Vestigial structures – are remnants of structures that may have had important functions in an ancestral species, but have no clear function in modern descendant.
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Similarities in Development• Embryos of closely related organisms have similar
states in development.
http://home.honolulu.hawaii.edu/~pine/book1qts/embryo-compare.jpg
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Genetics
• DNA & Protein analysis are new tools for testing evolution
• DNA passed from parents to offspring, so should show evolution (i.e. ancestry)
• Darwin hypothesized that all life forms are related. He was right and it is proven in the fact that DNA is the common language in which traits are passed.
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Hemoglobin Comparisons
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Answer these in your notes (5 min)
• Why are older fossils generally in deeper rock layers than younger fossils?
• How can evolutionary theory explain why Australia is home to relatively few native placental mammals?
• What are homologous and vestigial structures?• What can you infer about species that differ
significantly in their DNA sequences?
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Natural Selection
• Population – a group of individuals of the same species living in the same area.
• “Survival of the Fittest”
http://www.truthinscience.org.uk/site/images/stories/peppered%20moth.jpg
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Artificial Selection
• Definition – Selective breeding of domesticated plants and animals to produce offspring with genetic traits that humans value. – Chickens that weigh too much– Dogs with aggression– Dogs with keen sense of smell and longing to
retrieve– Plants that are not susceptible to pesticides
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Pesticides – Natural Selection in Action
• Pesticides are poisons used to kill pests– Insecticides– Rodenticides– Etc
• A little poison will kill 99% of “pests” the first time
• Second time it’s not as successful. Why?
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Inherited Resistance
http://upload.wikimedia.org/wikipedia/commons/thumb/8/85/Pesticide_resistance.svg/573px-Pesticide_resistance.svg.png
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Affects of Pesticides
• Birth Defects
• Cancer• Stronger
Resistance• Affects
Native Species
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Gene Pools• Consist of all the alleles (genes) in all the
individuals that make up a population.
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Changes in Gene Pools
• Mutations• Sexual recombination
– Promotes survival and reproductive success– Some alleles become more common
• Ex. Peppered Moth
• Microevolution – A generation-to-generation change (over a short time)
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Genetic Drift
• A change in the gene pool of a population due to chance.– Occurs more drastically in smaller populations
• Ex. Coin toss• 10 x’s vs 1,000 x’s
• The Bottleneck Effect – Disasters such as earthquakes, floods, droughts and fires may drastically reduce the size of a population, which reduces the size of its gene pool.
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Bottleneck Effect
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Mutations
• Change in the DNA of an individual, which in turn can change a population over great time.
• Influenced by natural selection or genetic drift.
• Darwinian fitness = the contribution that an individual makes to the gene pool of the next generation.
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Interesting Mutations• Sickle cell disease• Antibiotics and Bacterial Resistance
– Tuberculosis
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Interesting Mutations cont’d
http://news.softpedia.com/images/news2/Researchers-discover-how-to-detect-mutations-2.jpg
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