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How Populations Evolve Before Darwin – 2 main ideas 1. Species are fixed – not changing 2. Earth relatively young - <10,000 yrs These ideas began to change as people studied organisms, fossils, geology, and human population growth Organisms – Greater diversity than previously known Fossils – Suggest old Earth, Fossils similar to existing organisms Geology – Gradual and observable geologic events (weathering/erosion, earthquakes) could explain current physical features. Darwin Dec. 1831 HMS Beagle – 5 year voyage Darwin’s Job: Study geology, plants and animals during voyage Send samples home to England Data/observation convinced him species changed as they adapt to their environments o Not the individual, but the population Darwin documented regional differences o Fossils of South America more similar to South American species Islands were of particular interest o Island organisms similar to nearest mainland Made geologic observations o Experienced earthquake and resulting uplift of ocean floor o Collected shells on mountain tops Back in England Combined observations from voyage with problems from human population growth o Organisms produce more offspring than environment can support This leads to a struggle for survival 2 Main Points 1. Descent with Modification – organisms alive today are descendants of ancestral species. o Different habitats result in an accumulation of different traits (modification) 2. Natural Selection - Those organisms with inherited characteristics best suited for that environment survive better and pass on those traits/genes to their offspring. o Adaptation – Inherited characteristics that improve an organism’s ability to survive and reproduce in a specific environment. Characteristics must already be present in the population (variation). Giraffe Evolution How is artificial selection different from natural selection? Humans act as the selective pressure – select for traits they want in the next generation. Wild mustard: o broccoli, cauliflower, cabbage, Brussels sprouts and kale Dog breeds ? Using genetic tests, scientists now know that dogs and wolves share a common ancestor, not a direct lineage. This common ancestor was a prehistoric wolf that lived in Europe or Asia between 9,000 and 34,000 years ago. Evidence for Evolution 1. Fossil Record What types of parts generally fossilize? o Hard parts: teeth, bones, shells o Rarely soft tissue and markings How do fossils form? A. Petrification - Organism dies and minerals from groundwater invade the organic tissue and turn the organism to stone. B. An organism dies and is covered by sediments. Organic tissue decays and leaves an empty mold Minerals from water fill mold and solidify C. Other fossils can be formed in resin amber, ice or acid bogs. a. At times organic tissue can be preserved Rock Strata and the Fossil Record Sedimentary rocks form from the compaction of sand, mud and other rocks over time. New sedimentary rock layers are formed on top of old layers o The rock layers are called strata Young strata found above older strata* Fossils found in lower layers are older than fossils found in higher layers – Relative age Radiometric dating uses radioactive isotopes can be used to determine the actual age of rock or fossil. Oldest fossils are prokaryotic cells from 3.5 billion years ago. Fossil Record Evolution of the Horse Whale Evolution 2. Molecular Biology Heritable information is stored in DNA Siblings are more closely relate (genetically) to each other than two unrelated members of the same species The more similar the DNA sequences of two species the more closely related. o Greater differences means less closely related If you can’t use DNA, what else could be used? Proteins – Why? DNA RNA Protein 3. Biogeography – organisms are more similar to those living in close proximity than to organisms living further away. Galapagos animals and South America Australian marsupials, Plant distribution Galapagos Finches Mockingbirds of the Galapagos Islands. 4. Homologous Structures / Comparative Anatomy Homologous structures – structures shared by organisms because of a more recent common ancestor. Function can be different Mammal forelimb - all contain the same bones, but limbs used for different functions Vestigial structures – structures with no clear or current function but served a purpose in an ancestor. o Whale hind pelvis o Snakes with pelvis o Flightless birds/insects with wings o Blind cave fish with eyes o Human tailbone o Human goose bumps Analogous Structures Don’t show close evolutionary relationships 5. Embryology Embryology is the study of how multicellular organisms develop from an embryo towards an adult. Study the rate of bone/structure development Observe the pattern of development All vertebrates have gill pouches In fish – become gills In terrestrial animals – skull bones Organisms more closely related share more similar stages of development Artist rendering of concept Natural Selection http://peppermoths.weebly.com/ What could account for the change in beak depth over time? Precipitation food availability beak depth Natural selection “edits” traits already in the population Natural selection is specific to time and location Natural selection can change populations quickly Natural Selection - Those organisms with inherited characteristics best suited for that environment survive better and pass on those traits/genes to their offspring. Adaptation – Inherited characteristics that improve an organism’s ability to survive and reproduce in a specific environment. Characteristics must already be present in the population (variation). Populations and Evolution What makes a population? Organisms of the same species o Species – organisms that can reproduce together and produce fertile offspring Living in the same place at the same time Why is this important? Must be able to sexually reproduce – pass on “favorable” genes to future generations Population genetics – study how populations change genetically over time. Gene pool – the total collection of genes in a population at any one time. The gene pool consists of all the alleles in all the individuals making up a population Microevolution – when the relative frequencies of alleles in a population change over generations