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Evolution Topics 5.1-5.4 Evolution • Definition : Evolution is the cumulative change in the heritable characteristics of a population. • Charles Darwin developed his theory in The Origin of Species, published in 1859. • The theory of natural selection can be explained in a series of observations and deductions. Evolution Topics 5.1-5.2 Darwin’s Observations and Deductions Observation • Populations of living organisms tend to increase exponentially. • However, the number of individuals in populations remain nearly constant. Deduction • More offspring are produced than the environment can support. There is a struggle for existence in which some individuals survive and some die. Darwin’s Observations and Deductions Observation • Living Organisms vary. The members of a species are different from each other in many ways. • Some individuals have characteristics that make them well adapted to their environment and other individuals have characteristics that make them less well adapted to their environment. Deduction • The better adapted individuals tend to survive and reproduce more than the less well-adapted individuals. • (a.k.a. Natural Selection) Darwin’s Observations and Deductions Observation • Much variation is heritable – it can be passed on to offspring Deduction • The better-adapted individuals pass on their characteristics to more offspring than the less well adapted individuals. The results of natural selection therefore accumulate. • As one generation follows another the characteristics of the species gradually change – the species evolves. Sexual Reproduction Driving Evolution • Variation is necessary for natural selection – Mutation : original source for new genes – Meiosis : greater opportunity for variation because of independent assortment. • Species that produce asexually still produce some variation primarily through mutation. – Potential for evolution is much less. Evidence: Homologous Structures • Homologous Structures are structures that are similar in different species but come from common ancestry. Fossil Records • Comparison of the skulls of a human (left column) and the capuchin monkey (right column). Selective Breeding Method of improving a species by allowing only those individual organisms with desired characteristics to produce the next generation. How does selective breeding give evidence to evolution? Evolutionary Response to the Environment • Many organisms will evolve in response to the environment. – This is typically an environmental threat to the species. – Struggle for survival leads to evolution(change in traits seen) • Examples: – – – – Galapagos Finches Pesticide Resistance Heavy Metal Tolerance in Plants Antibiotic Resistance Antibiotic resistance • Direct exposure to antibiotic does NOT produce resistance • Bacteria that have a natural resistance to the antibiotic survive exposure and reproduce offspring • Those that are not naturally resistant die when exposed to antibiotics. No new off spring produced • What remains is a population of resistant bacteria. ( they “evolved”) Terminology • Gene Pool: – All of the genes in an interbreeding population. • Allele Frequency – The number of times a particular allele appears in a give population • Species – A group whose members possess similar anatomical characteristics and have the ability to interbreed. Speciation • The formation of a new species as a result of a preexisting species spliting. • Two types of speciation: – Sympatric : same geographical location – Allopatric : different geographical location • This usually results from populations becoming isolated from the rest of their species. • This is most commonly seen when populations migrate to areas that are geographically isolated from their original territory or different ecologically. Geographic Isolation Speciation • Endemic species are species that exist in only one place. – Ex. Galapagos Islands • Galapagos Finches – 4 Endemic Species • Lava Lizards – 7 Endemic Species that live on twelve different islands Classification Topic 5.3 Classifying Organisms • Advantages to classifying organisms – Species Identification • Easy to find out which species an organisms belongs to – Predictive Value • Species in the same grouping will have similar characteristics – Evolutionary links • Groups with similar characteristics most likely evolved from a common ancestor. Possible to predict evolution by classifying organisms. Classification • 1959 - 5 kingdoms established. • Based on physical characteristics seen by scientists Reclassification • 1989 Carl Woese studied the molecular relationships (RNA) between organisms • Established 3 Domains: * Eubacteria * Archaea * Eukarya Characteristics of the 3 domains Charactersitic Eubacteria Archaea Eukarya histones absent histone-like proteins present introns absent present in some DNA present size of ribosome 70S 70S 80S structure of cell membrane lipids unbranched hydrocarbons some branched hydrocarbons unbranched hydrocarbons peptidoglycan in cell wall present absent absent membrane-bound organelles absent absent Present Taxa • Group of organisms (ex. Species) is called a taxon. • Organisms are classified into a series of taxa. There is a hierarchy of taxa. • The first taxa is the most specific (Homo sapiens) and the last taxa is the most general (Kindom Animalia) • There are seven levels of taxa Binomial Nomenclature • Naming system adopted by Carolus Linnaeus in the 1700’s. • Nomenclature : name given to a species • Binomial : Two names are used for naming • Binomial Nomenclature = Naming system where two name are used to name each species Binomial Nomenclature continued • • • • • • Homo sapiens First name is the genus name First name is given an upper-case first letter Second name is the species name Species name is given a lower case first letter Italics are used when the name is printed Name is underlined if it is handwritten Levels of Hierarchy for Eukaryotes (general to specific) • • • • • • • Kingdom Phylum Class Order Family Genus Species Examples Humans Garden Pea • • • • • • • • • • • • • • Kingdom Animalia Phylum Chordata Class Mammalia Order Primate Family Hominidae Genus Homo Species Sapiens Kingdom Plantae Phylum Angiospermae Class Dicotyledonae Order Rosales Family Papilionaceae Genus Pisum Species sativum Dichotomous key Dichotomous key Dichotomous key Dichotomous key Cladistics Topic 5.4 Cladistics • A clade is a group of organisms that have evolved from a common ancestor • Evidence can be seen from gene base sequences or amino acids sequences • Sequence changes accumulate so there is a positive correlation between the number of differences and the amount of time since 2 species diverges (molecular clock) Molecular clock Homologous vs. Analogous Traits • Homologous traits are similar due to ancestry • Example; chicken wing, human arm • Analogous traits are similar due to convergent evolution • Octopus eye and human eye Cladograms • Tree diagrams based on similarities and differences between species in a clade • Based on amino acid/DNA sequences as opposed to structural features • Branching points are called nodes (hypothetical split of species) Cladograms Cladograms Cladograms