Transcript Evolution
Darwin and Natural Selection Before Darwin… - People believed that species were stagnant and that Earth was only 10,000 yrs. old and also unchanging -1700’s Georges Buffon used fossils to say the Earth was much older than a couple thousand years -1800’s Jean Baptiste Lamarck founded the theory of evolution (he was wrong) Charles Darwin Designed theory of natural selection (not the theory of evolution) based on observations of nature Expanded upon Lamarck’s evolution and disproved conventional wisdom of the time Darwin’s 2 main points 1. 2. Descent with modification: all species are derived from a common ancestor, but over time they have changed and adapted Natural Selection: individuals with characteristics more suited to the environment reproduce more, passing on their trait Natural Selection- 4 key concepts Variation: Organisms (within populations) exhibit individual variation in appearance and behavior. These variations may involve body size, hair color, facial markings, voice properties, or number of offspring. On the other hand, some traits show little to no variation among individuals—for example, number of eyes in vertebrates. Inheritance. Some traits are consistently passed on from parent to offspring. Such traits are heritable, whereas other traits are strongly influenced by environmental conditions and show weak heritability. High rate of population growth. Most populations have more offspring each year than local resources can support; leading to a struggle for resources. Each generation experiences substantial mortality. Natural Selection- 4 key concepts How many moths? Differential survival and reproduction. Individuals possessing traits well suited for the struggle for local resources will contribute more offspring to the next generation. Bacteria evolve through natural selection too! Coevolution Coevolution Definition Coevolution is a change in the genetic composition of one species (or group) in response to a genetic change in another. The two species must interact with each other within the same ecological system or community As they interact, the two species must put pressures on each other The Two Species Must Interact With Each Other There are several ways different species interact Two plant species may be vying for soil, sunlight or water Two animal species may be vying for the same food source, territory or one might be the predator to the other An animal species may be feeding on a particular plant species A parasite species may favor a particular plant or animal species As They Interact, the Two Species Must Put Pressures on Each Other What is the difference between biotic and abiotic evolution? Biotic pressures include predation or competition for resources (possibility of coevolution) Abiotic pressures are non-living environmental features such as snow, extreme temperature changes and chemical pollution (possible simple adaptation) Simple Adaptation The snowshoe hare changes its coat twice per year to be less conspicuous to predators such as the bobcat The bobcat hasn’t adapted any particular change in vision to overcome this adaptation in the hare Coevolution Some populations of the newt have developed tetrodotoxin in their skin for use as a defense The garter snake preys on the newt in each community they are found together Some communities have no toxin while others have what seems to be overkill WHY? Microevolution Evolution on a small scale A change in gene frequency in one specific population If you could zoom in on one branch of the tree of life, you could continue zooming in until you saw the relationships between specific populations. But how do you know when you’ve reached the population scale? Population: A group of organisms that interbreed with each other. This could mean a group of animals on an island, a pair of animals that will mate, or anything in between. Artificial Selection a process in which humans purposefully select organisms for reproduction to either keep or lose traits. Mutation a change in a DNA sequence, usually occurring because of errors in replication or repair. Mutation is the ultimate source of all genetic variation. Gene flow the movement of genes between populations. This may happen through the immigration and emigration of organisms Natural selection A process in which some individuals have genetically-based traits that improve survival or reproduction and thus have more offspring surviving to reproductive age than other individuals. Genetic drift random changes in the gene frequencies of a population from generation to generation. This happens as a result of sampling error—some genotypes just happen to reproduce more than other genotypes. This process causes gene frequencies in a population to drift around over time. What is a species? A population or group of populations that can breed with each other and produce fertile offspring + + + + Fossils How are fossils made? Fossil making in action http://www.flmnh.ufl.edu/fhc/layer2.htm Fossils can come from either body parts or traces like nests, footprints, burrows, etc. 4 Types of Fossils - 1.Mold fossils 2.Cast fossils 3.Trace fossils - 4.True form fossils Mold fossils A mold of the organism is made in a substrate (some sort of lasting material) Cast Fossils When a mold fossil is filled in Trace Fossils Fossils made by signs that the animal existed instead of its actual body parts True form fossils Fossils made of the actual animal or animal part How are fossils made? Trapped in amber (hardened sap) Coalification- carbon is the only element left Replacement- hard parts dissolve, replaced by minerals like iron, calcite, silica Petrificationminerals form rock like fossil Molds Recrystalization How do we know how old a fossil is? How deep is it buried Relative dating Radioisotope dating Carbon 14 Uranium 235 Stratigraphy Dating fossils based on where they lie in sediment Relative Dating Radioisotope dating An estimate of a rock's age can be determined by examining the ratios of the remaining radioactive element and its daughters. For example, when lava cools, it has no lead content but it does contain some radioactive Uranium (U-235). Radioisotope dating Over time, the unstable radioactive Uranium decays into its daughter, Lead-207, at a constant, known rate (its half-life). By comparing the relative proportion of Uranium235 and Lead-207, the age of the igneous rock can be determined. Carbon-14 (which decays to Nitrogen-14) is also used to date fossils. Example The half life of Carbon-14 is about 6000 years. If a fossil contained 50% of the original carbon-14, how old is the fossil? If a fossil contained 75% of the original carbon-14, how old is the fossil?