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CHAPTER 15 Skim read pg. 418-422 EVOLUTION 15.1 Darwin’s Theory of Natural Selection Darwin on the HMS Beagle Darwin’s role on the ship was as naturalist and companion to the captain. His job was to collect biological and geological specimens during the ship’s travel His visit to the Galápagos Islands help him form his ideas about Natural Selection Here he found a strange assortment of plants and animals. The islands are located 1000 kilometers West of South America. They are many islands all with different climates because they all have different elevations. The Galápagos Islands 1.Darwin began to collect mockingbirds, finches, and other animals on the four islands. 2.He noticed that the different islands seemed to have their own, slightly different varieties of animals 3.At first nothing jumped out at him as significant but as he traveled back to England he began to think that the animals on the different islands could have once members of the same species. Darwin Continued His Studies After Returning Home: Almost every specimen that Darwin had collected on the islands was new to European scientists. He came to believe that populations of birds and animals from the mainland (South America) changed after reaching the Galápagos. Darwin hypothesized that new species could appear gradually through small changes in ancestral species. Darwin inferred that if humans could change species by artificial selection (such as, selecting cows that produce the most milk for breeding) then perhaps the same process could work in nature. The Galápagos Islands 15.1 Darwin’s Theory of Natural Selection Natural Selection Individuals in a population have variations ( Tall/ Short) Variations can be inherited (Families tend to have similar traits) Organisms that can survive on the available resources will have offspring and will pass on their traits Variations that increase reproductive success will have a greater chance of being passed on. The Origin of Species- written by Darwin Darwin published On the Origin of Species by Means of Natural Selection in 1859. Darwin’s theory of natural selection does not have the same meaning as evolution It is a means of explaining how evolution works At his time in history most Europeans believed that: The Earth and all living creatures were divine creatures put on Earth a few thousand years ago in just one week. That all creatures have remained exactly as they were when they were put on the Earth. Natural Selection Video Clip http://www.pbs.org/wgbh/evolution/educators/teach studs/svideos.html 15.2 Support for Evolution 1. The fossil record Fossils provide a record of species that lived long ago. Fossils show that ancient species share similarities with species that now live on Earth. Glyptondt Armadillo Evidence of Evolution contin. 2. Derived traits are newly evolved features, such as feathers, that do not appear in the fossils of common ancestors 3. Ancestral traits are more primitive features, such as teeth and tails, that do appear in ancestral forms Homologous Structures 4. Anatomically similar structures inherited from a common ancestor are called homologous structures. 5. Vestigial Structures Structures that are the reduced forms of functional structures in other organisms. Evolutionary theory predicts that features of ancestors that no longer have a function for that species will become smaller over time until they are lost. 6. Analogous Structures Analogous structures can be used for the same purpose and can look similar in construction, but are not inherited from a common ancestor. Show that functionally similar features can evolve independently in similar environments FLY EAGLE 7. Comparative Embryology http://www.pbs.org/wgbh/nova/evolution/guess-embryo.html Vertebrate embryos exhibit homologous structures during certain phases of development but become totally different structures in the adult forms. 8. Comparative Biochemistry Common ancestry can be seen in the complex metabolic molecules that many different organisms share. Ch. 15.2 Continued…… 15.2 Geographic Distribution The distribution of plants and animals that Darwin saw on his voyage suggested that evolution had occurred 15.2 Adaptation Adaptation is a trait shaped by natural selection that increases an organism’s reproductive success. Fitness: is a measurement of the number of reproductively viable offspring an organism produces The better the organism is adapted to its environment, the greater is chances of survival and reproductive success Adaptations for survival Poisonous Camouflage: adaptation that allows the organism to blend in with it surroundings to avoid getting eaten. Mimicry: One species evolves to resemble another species Both of this increases survival- so the organism will be able to reproduce Nonpoisonous Mimicry and New Technologies http://www.nbcnews.com/tech/innovation/spider- web-bandages-new-medicine-mimics-nature-n69141 15.3 Shaping Evolutionary Theory Mechanisms of Evolution Hardy-Weinberg principle states that when allelic frequencies remain constant, a population is in genetic equilibrium Genetic Drift: A change in the allele frequencies in a population that is due to chance In smaller populations, the effects of genetic drift become more pronounced, and the chance of losing an allele becomes greater. Types of genetic drift: 1. Founder effect 2. Bottleneck Founder Effect: Occurs when a small sample of a population settles in a location separated from the rest of the population Alleles that were uncommon in the original population might be common in the new population Example: Amish and Mennonite communities in the U.S. rarely marry outside of their community. Higher incident of 6 fingered dwarfism. “Darwin’s Finches” Bottleneck: Occurs when a population declines to a very low number and then rebounds Example: Cheetah’s: population declined 100 years ago and then rebounded. The cheetahs are so genetically identically they appear inbred. Can lead to extinction due to an increase of genetic defects and a decrease in fertility Gene Flow: Is caused by the random movement if individuals between populations. This increases genetic variation within a population and reduces differences between populations Nonrandom Mating: rarely is mating completely random. Individuals usually mate with other that are in close proximity. This can promote inbreeding and lead to a change in allele frequency. Mutations Mutations are the raw material for natural selection. Mutations occur randomly but can affect the allele frequency in a population. Sometimes the mutation is harmful to a population and sometimes it is helpful. Example: Giraffe's long necks Natural Selection: Acts to select the individuals that are best adapted for survival and reproduction Three types of Natural Selection: 1. Stabilizing Selection: 2. Directional Selection 3. Disruptive Selection 1. Stabilizing Selection: Stabilizing selection operates to eliminate extreme expressions of a trait when the average expression leads to higher fitness. Example: human birth weight- babies born with above-normal and below – normal birth weights have a decreased chance for survival 2. Directional Selection: Directional selection makes an organism more fit Example: The peppered moths- They existed in two color forms (light and dark winged). When the environment changed and favored the dark winged moths, the light winged moths were more likely eaten and they decreased in number. 3. Disruptive selection: Disruptive selection is a process that splits a population into two groups and tends to remove the individual with average traits Example: Size of beetles: Smaller than average can hide more easily. Larger than average are more difficult to eat. Medium size are more likely to be eaten. Darwin added one more form of Natural Selection: Sexual selection operates in populations where males and females differ significantly in appearance. Qualities of sexual attractiveness appear to be the opposite of qualities that might enhance survival Example: Peacock feathers seem as though it would make it more difficult for the bird to flee from a predator Reproductive Isolation: Speciation: Is the process that some members of a sexually reproducing population change so much that they can no longer produce fertile offspring with members of the original population. Two types: 1. Prezygotic isolation: this prevents reproduction through geographic, behavioral, ecological or other differences. (before mating) Eastern and Western Meadowlark Reproductive Isolation: 2. Postzygotic isolation: after mating has occurred, the hybrid individuals are not able to reproduce themselves. Example: A tiger and lion can mate but the Liger cannot reproduce (it is sterile) MATING OF A HORSE AND DONKEY PRODUCES A MULE WHICH IS STERILE • LIGER WHAT MADE THIS? Speciation: For speciation to occur the population must diverge ( separate) 1.Allopatric speciation A physical barrier divides one population into two or more populations Speciation: 2. Sympatric Speciation: A species evolves into a new species without a physical barrier. The original species and the new species live side by side during the speciation process Example: Apple fly maggots are diverging based on the type of fruit they eat Adaptive Radiation Can occur in a relatively short time when one species gives rise to many different species in response to the creation of new habitat or some other ecological Opportunity • Often follows large-scale extinction events. (Mammals following the extinction of the dinosaurs) One species gave rise to many new species of cichlid fish Coevolution: The relationship between two species might be so close that the evolution of one species affects the evolution of the other species. The two types of symbiotic relationships that are often involved in coevolution are: Mutualism and parasitism Example: A moth that gets food from a specific flower and in turn pollinates that flower – both have coevolved to create this relationship Convergent Evolution: Unrelated species evolve similar traits even though they live in different parts of the world. Occurs when the environments the individuals live in are similar even though geographically they are far apart How Fast do evolution occur? 1. Punctuated Equilibrium 2. Gradualism: Rapid evolution in Evolution occurs slowly short periods of time & some periods of time when evolution occurs slowly over many, many years