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Transcript
Evolution Overview Charles Darwin • Proposed the Theory of Evolution • Evolution-gradual change in a species through adaptations over time • Theory of Evolution= Natural Selection Natural Selection • Natural selection is based on the following ideas: – natural variation – production of more offspring than can survive – competition for resources, and to escape predators – differential survival based on traits • Organisms with traits well suited to an environment are more likely to survive and produce more offspring than organisms without these favorable traits. Evidence for Evolution • Evolution occurs over millions of years and cannot be seen in one lifetime • Scientists rely on evidence to support the Theory of Evolution 1.) Adaptations • Adaptation- structure or behavior that helps an organism better survive in its environment. • Mimicry- a structural adaptation that enables one species to resemble another species. • Camouflage- a structural adaptation that allows a species to blend in with its surroundings • Physiological Adaptationchanges in an organism’s metabolism that occurs quickly. Many bacteria have become resistant to penicillin over the last 50 years 2.) Fossil Record • Fossil-trace of a dead organism. Examples bones, dinosaur track, insects trapped in tree sap, impressions of leaves, animals buried in tar or ice • Give clues are to what ancient organisms looked like • Compare fossils to organisms we know today • Today’s species had to evolved from ancient species 3.) Comparative Anatomy • Homolgous Structuresbody structures on different organisms that are similar in structure or function and evolved from the same ancestor • Analogous StructuresBody structures on different organisms that are similar in function but did not evolve from the same ancestor. • Vestigial StructuresBody structure in an organism that no longer serves its original purpose but was useful to the ancestor • Embryo- earliest stage of growth and development of both plant and animals • Human embryos and embryos of all other vertebrates are very similar which suggests that all vertebrates are related • Nearly all organisms have DNA, ATP, and many of the same enzymes • The DNA of closely related organisms looks very similar Natural Selection • Occurs in populations over time not individuals • Population- all the members of a species that live in an area • Gene Pool- all of the alleles of the population’s genes • Genetic Equilibrium- the frequency of alleles remains the same over generations • Populations in genetic equilibrium are not changing so they are not evolving • Anything that changes the genes in the populations gene pool will cause evolution to occur What Causes Changes in the Gene Pool? • 1. Mutations that occur by chance or by radiation and chemicals • 2. Genetic drift: frequency of alleles are changed by random events in an isolated population • 3. Gene flow: the transport of genes by traveling individuals • 4. Non-random mating: Individuals selecting mates with specific heritable traits (sexual selection) • 5. Natural selection 3 Conditions of Natural Selection • Struggle for existence: more offspring are produced than can survive so organisms compete for survival • Natural variation among individuals • Survival of the fittest 3 Types of Natural Selection • Stabilizing selection: favors average individuals in a population • Directional selection: favors one of the extreme variations of a trait • Disruptive/diversifying selection: favors individuals with either extreme of a trait Speciation • Evolution of a new species that occurs when members of similar populations no longer breed with each other to produce fertile offspring • There are several reasons why similar populations no longer breed – Geographic isolation: when a physical barrier (lava from volcanic eruptions, sea level changes, etc.) divides a population • Reproductive isolation: occurs when organisms no longer breed with each other to produce fertile offspring because of – Differences in genes – Mating times change – Different numbers of chromosomes How fast does speciation occur? • Gradualism: idea that species originate through a gradual change of adaptations (longer than 10,000 years) • Punctuated equilibrium: idea that species originate in rapid bursts (10,000 years or less) with long periods of genetic equilibrium in between Two types of evolution • Divergent evolution (adaptive radiation): species that once were similar become increasingly different • Convergent evolution: distantly related organisms evolve similar traits