Origin of Life

Theories of Evolution Lamark’s Explanation a. believed that traits were “acquired” and not determined by genes b. traits were results from organisms experiences or behavior c. “necks of giraffes”

Charles Darwin’s Theory of Evolution Galapagos Islands a. Darwin’s finches

Origin of Species by Natural Selection – by Charles Darwin Evolution – concept that species have changed over time

Natural Selection “organisms best suited to their environment reproduce more successfully than other organisms” 1. Adaptation 2. Fitness -competition *selection conditions change as the demands of the environment change *if environmental change is too extreme, populations cannot adapt quickly enough and they become extinct

Patterns of Evolution Genetic Drift – the alteration of allele frequencies by chance events Punctuated Equilibrium – speciation occurs during brief periods of rapid genetic change

Divergent Evolution – two or more related populations or species become more and more dissimilar - domestic dogs Convergent Evolution – 2 organisms seem to be similar but are not at all - shark and porpoise Co-Evolution – 2 species evolve together - plants and the animals that pollinate them

Evidence of Evolution

Evidence from Living Organisms Homologous and Analogous Structures a. Homologous – similar features that originated in a shared ancestor Homologous features can result from modifications that change an original feature to two extremely different types (ex. Wing and arm); shows that the two features could have shared a fairly common ancestor

b. Analogous- features serve identical functions and look somewhat alike

Vestigial Organs “useless features” a. appendix b. human tailbone

DNA and Chemical Studies a. human and chimp DNA – very similar Embryo studies a. all vertebrae embryos are similar at 4 weeks b. all vertebrates have gill slits at 4 weeks

Types of Natural Selection Stabilizing Selection * individuals with average form of a trait have the highest fitness  most common Directional Selection * individuals that display a more extreme form of a trait have greater fitness than individuals with an average form of trait Disruptive Selection * individuals with either extreme variation of a trait have greater fitness than individuals with the average form of the trait Genetic equilibrium – allele frequencies in a population tend to remain the same from generation to generation unless acted on by outside influences *natural selection is the single most important factor that can disrupt genetic equilibrium.  stabilizing selection: the average represents the optimum for most traits example: blue curve represents the population after a new predator has come in small lizards may not survive because they can get away fast enough AND large lizards may not survive because they can be spotted the easiest. This is why it is an advantage to be average size. Directional selection: tends to eliminate one extreme of phenotypes example: anteaters feed by breaking open termite nests extending their tongue. If there was a new termite that came in with a VERY deep nest, only the anteaters with the extremely long tongue would be able to feed off of the termite and the other anteaters would not survive. Disruptive selection: eliminates intermediate phenotypes example: shell color on limpets (type of shell). The shell color varies from white to dark tan. The white shelled limpets that are on rocks covered with goose barnacles (white as well) are protected because they blend in, the shells that are dark tan and are on the dark rocks are also protected because they blend in. The intermediate color limpets are not protected because they stand out on light colored rocks as well as dark colored rocks.