B Evolution Classification Part 2

Evolution Evolution: • A change in heritable traits over many generations • Process by which modern organisms descended from the first life form • An explanation regarding the beginnings of life Theory: • Guess/explanation of what is observed from facts and inferences • Fact  direct evidence • Inference  indirect evidence Proportions of Theories 1. Must explain the observations using cause & effect 2. Theories are made to predict future cycles 3. Based upon other/previous theories 4. Theories must change if they are no longer able to explain future cycles Evolutionary Theory A collection of carefully reasoned & tested hypothesises about how evolutionary change occurs Theories Jean Baptiste de Lamarck (1744-1829)

• All organisms have an innate desire to change • Use & Disuse – change occurs because organisms can alter their shape in new ways; if animals didn’t use a body part, it would disappear or shrink • Inheritance of acquired traits

Charles Lyell

• large periods of time is required to explain the changes in species from a common ancestor • implies that the earth is very old

Artificial Selection

• farmers ensured that only individuals with desirable traits would reproduce

Thomas Malthus (1766-1834)

• population control • rate of birth > rate of death • explanations: disease, war, famine

 James Hutton

• changed in the Earth were caused by erosion, weathering, and temperature

Darwin (1809-1882)

• travelled to Galapagos Islands to study the animals • 1858 published book: “Origin of Species by means of Natural Selection” 1. Descent with modifications • Common descent • All species descended from only 1 original life form 2. Natural Selection • Mature killed off species that did not have the traits to survive, allowing those with the right traits to reproduce • 4 supporting points 1. overproduction • Malthus influence Darwin • Id every seed was to bear fruit, there would be more trees than land • Environmental factors influences evolution 2. genetic variation • A population must be composed of individuals with different traits 3. survival and adaptation • Variations allowed some to survive where others died • Adaptation: inheritance of these traits 4. differential reproduction • Nature decides which traits will survive “survival of the fittest”

Natural Selection • Artificial Selection: humans decided which traits would be useful for a population • Natural Selection: environmental factors influenced survival of important traits 1. Stabilizing Selection • Average form of a trait has the highest fitness • Fitness: the ability to pass on your genes (more children = more fitness) 2. Disruptive Selection • Extreme variations of a trait have the greatest fitness 3. Directional Selection • Individuals with a more extreme form would have greater fitness Other Influences 1. Non-random mating • Individuals should mate with others whose traits are similar to their own

• Influences which genes would be helpful in nature 2. Sexual Selection • Females would choose males based on specific desirable traits Fossils Fossil: the remains or traces of a once-living organism; preserved by being encased by a protective environment Sedimentary Rock: formed when small rocks such as sand, silt, or clay layers on top of one another Fossils form when animals: • fall into crevices & died & was buried • trapped in ice • trapped by tree sap • bogs & swamps Fossils aren’t always the body parts of an organism: • Imprint: a type of fossil in which a thin film of carbon remains after the organism has decayed. • Mold: a type of fossil formed from an impression of the shape or tracks of an organism • Cast: a type of fossil formed when sediments fill in the cavity left by a decomposed organism Dating Fossils 1. Relative Age The relative age of fossils is determined from their position in the sedimentary rock. In undisturbed sedimentary rock the bottom layers are the oldest and the top layers are the youngest. Therefore fossils found in the lower layers are older and the ones found in the upper layers are younger. Thus a fossil’s position in sedimentary rock beds gives its age relative to other fossils. 2. Absolute Age The absolute age of a fossil is determined by dating the fossil with radioactive isotopes Radioactive Isotopes: • have unstable nuclei that decay and form other elements • decay at a constant, known rate • Half Life: the period of time it takes for one-half of the radioactive material to decay • Carbon 14, Potassium 40, Uranium 238 The Fossil Record Law of Superposition • Oldest layer is at bottom

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Youngest layer is at top

Geological Time Scale • Dating fossils by dating the rock they’re found in Speciation Speciation: formation of species and relating them to shared ancestors Morphology • Using internal and external structures as criteria to classify species • Problems: different species may interbreed to produce a hybrid offspring Biological Species Concept • A species is defined as a population of organisms that can successfully interbreed but cannot breed with other groups Patterns of Evolution 1. Divergent Evolution • Descendants of a single species diversified into different species to fit into the various niches in the environment • Adaptive radiation: produce species that are physically different but internally similar 2. Convergent Evolution • Different species evolved similar traits • Species with different origins evolved similar traits with different functions 3. Co-Evolution • 2 or more species evolve together and influence each others’ traits 4. Artificial Selection • Humans decide which traits of a species will dominate Isolation Geographic Isolation • physical separation of the species (mountains, rivers, canyons) • allopathic speciation: new species develop due to geographic speciation Reproductive Isolation • population becomes genetically different without geographic barriers • sympatric speciation: species arise within the same geographic area • 2 types: 1. Postzygotic Isolation: 2 interbreeding species are so genetically different that the offspring may die or may be infertile

2. Prezygotic Isolation: factors present species from breeding before mating Rates of Speciation 1. Gradualism: speciation occurs at a graduated rate 2. Punctuated Equilibrium: rapid & sudden change in a very short period of time DNA Evidence Hardy-Weinberg Genetic Equilibrium Theory • Willheim Weinberg and Godfrey Hardy • Theory explains that DNA frequencies in a population remains the same throughout time unless it is influenced by external factors • Required Factors (theoretical model that cannot exist) 1. no mutations 2. individuals do not enter or leave the population 3. population is large 4. random mating 5. no selection Gene Pool • total genetic information where members can interbreed and share genes • allele: a gene that gives rise to a physical trait (phenotype) • allele frequency: the number of times the allele for the same gene occurs • evolution occurs when the allele frequency changes Causes of Variation 1. Mutations: change in DNA • 3 types: 1. positive mutation: helps in survival 2. neutral mutation: no benefit or deficit 3. negative mutation: most are negative; malfunctioning genes 2. Recombination of DNA: in meiosis genes can randomly swap, leading to different traits 3. Random Pairing of Gametes: random chance  males produce a large number of sperm competing to fertilize one egg 4. Mutagens: radiation or chemicals that alter DNA 5. Gene Flow: individuals move in (immigration) or move out (emigration), changing the genetic composition of the population Genetic Drift: allele frequencies change due to random events Small Populations • Do not have stable allele frequencies • More prone to change due to limited variation • Results in a larger genetic drift • May result in extinction due to lack of variation

Large Populations • Maintaining allele frequency due to large number of different alleles • Genetic drift is minimal

Problems with DNA Evidence • Similar organisms thought to be sharing common ancestors have very different DNA • Certain genes may be similar but the majority of genes are too different • Completely different organisms are genetically compatible DNA Evidence Homologous Structures • Structures or limbs that develop from the same body part but are specialized for an organism’s environment • Structures are similar in structure but not always similar in function • They are anatomical structures that occur in different species and that originated by heredity from a structure in the most recent common ancestor of the species Analogous Structures • Species from different origins sharing similar structures Vestigial Structures • Serve no function but resemble structures with functional structures in related organisms Embryology: Similarities in Early Development • Similar genes cause similar developmental stages • Since they derive from a common ancestor the genes come from the same ancestor • Over time the differences get greater and greater due to mutations