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EVOLUTION (Ch 16 & 17) Since formation of Earth (4.5 bya) there has been: Geologic evolution Organic Evolution The fossil record shows the order of which organisms were present on Earth (p 2 in packet) Practice Question: Organism X appeared on Earth much earlier than organism Y. Many scientists believe organism X appeared between 3 and 4 billion years ago, and organism Y appeared approximately 1 billion years ago. Which row in the chart below most likely describes organisms X and Y? Row 1 2 3 4 Organism X Simple multicellular Complex multicellular Unicellular Complex multicellular Organism Y Unicellular Simple multicellular Simple multicellular unicellular The Theory of Evolution: the process by which species have changed over time; resulting in the diversity on Earth today Evidence of the theory: 1) studying the fossil record Fossil: remains or traces of an organism that has been preserved (ice/mud) Most commonly found in sedimentary rock because they have been formed by layers over time (bottom layers=older) Paleontologists study fossils Comparing fossils to present day organisms we can see changes that have occurred…evolution 2) Comparative Studies: observations of similarities between various organisms; (structural = physical features; molecular = chemical makeup) a. anatomy: similarities in skeletal structure homologous structures: parts of different organisms that are similar in structure , but different in function vestigial structures: remnants of structures that were functional in ancestral form, showing there has been change over time ex: appendix b. biochemistry: studying molecules among species (ex: amino acid sequences in proteins) c. cytology: studying cell structures among species d. embryology: studying stages of development among species *Comparisons look for common ancestry between species* History of the Theory Lamarck (1809) – his 2 principles 1. law of use and disuse: the more an animal utilizes a structure, the better adapted it will become 2. inheritance of acquired characteristics: traits developed will also be passed on to offspring Charles Darwin: Evolution by Natural Selection His book: The Origin of species (1859) His theory: Natural Selection: process by which organisms having the best adaptive traits for a given environment are more likely to survive, reproduce, and pass their traits on to next generation; those not successful will die 5 main ideas of his theory: 1. overproduction – more born than will survive 2. competition for resources 3. survival of the fittest (those best adapted will survive) 4. reproduction – pass genes on to next generation 5. speciation: eventually evolution of a new species “descent with modification” Weakness of his theory: he couldn’t explain HOW the favorable variations arose Modern theory of Evolution = Darwin’s theory + genetics **the 2 sources of variations in a population: 1. mutations 2. Sexual reproduction Population genetics The frequency of alleles can change within gene pool of a population… o The alleles of favorable variations will increase over time o The alleles of unfavorable variations will decrease Can an individual evolve???? Practice Question: When is extinction of a species most likely to occur? (1) when environmental conditions remain the same and the proportion of individuals within the species that lack adaptive traits increases (2) when environmental conditions remain the same and the proportions of individuals within the species that possess adaptive traits increases (3) when environmental conditions change and the adaptive traits of the species favor the survival and reproduction of some of its members (4) when environmental conditions change and the members of the species lack adaptive traits to survive and reproduce