Study Materials Biology - Evolution

Study Materials Biology: Evolution 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. The Galápagos Islands • • Darwin began to collect mockingbirds, finches, and other animals on the four islands. He noticed that the different islands seemed to have their own, slightly different varieties of animals. • Almost every specimen that Darwin had collected on the islands was new to European scientists. • Populations from the mainland changed after reaching the Galápagos. Darwin Continued His Studies • • 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, then perhaps the same process could work in nature. Natural Selection • • • • Individuals in a population show variations. Variations can be inherited. Organisms have more offspring than can survive on available resources. Variations that increase reproductive success will have a greater chance of being passed on. The Origin of Species • • • Darwin published On the Origin of Species by Means of Natural Selection in 1859. Darwin’s theory of natural selection is not synonymous with evolution. It is a means of explaining how evolution works. Bell Ringer 4/25/13 Target Word Artificial Selection Natural Selection Evolution Adaptation Vocab Review Definition Main Idea Picking and choosing traits. INHERITANCE Variation Environment adaption Change over time!!!! Changing traits to for your environment. 1. Theory of evolution based on 4 ideas, excess reproduction, variations, inheritance, and advantages of specifics traits. 2. Organisms selected for certain traits in order to produce off spring having those traits. 3. Change in groups of living organisms over time. 4. Inherited characteristics of species that develop over time in response to an environmental factor allowing species to survive Vocabulary Word A. Evolution B. Adaptation C. Artificial Selection D. Natural Selection Evidence of Evolution Support for Evolution • • • 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. Glyptodont • • • Armadillo Derived traits are newly evolved features, such as feathers, that do not appear in the fossils of common ancestors. Ancestral traits are more primitive features, such as teeth and tails, that do appear in ancestral forms. Anatomically similar structures inherited from a common ancestor are called homologous structures. 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. Analogous structures can be used for the same purpose and can be superficially similar in construction, but are not inherited from a common ancestor. Show that functionally similar features can evolve independently in similar environments Comparative Embryology Vertebrate embryos exhibit homologous structures during certain phases of development but become totally different structures in the adult forms. Comparative Biochemistry Common ancestry can be seen in the complex metabolic molecules that many different organisms share. Comparisons of the similarities in these molecules across species reflect evolutionary patterns seen in comparative anatomy and in the fossil record. Organisms with closely related morphological features have more closely related molecular features. Geographic Distribution The distribution of plants and animals that Darwin saw first suggested evolution to Darwin. Rabbit • • Mara Patterns of migration were critical to Darwin when he was developing his theory. Evolution is intimately linked with climate and geological forces. Types of Adaptation • • An adaptation is a trait shaped by natural selection that increases an organism’s reproductive success. Fitness is a measure of the relative contribution an individual trait makes to the next generation. Camouflage Allows organisms to become almost invisible to predators Leafy sea dragon Mimicry One species evolves to resemble another species. Western coral snake California kingsnake Bee Orchid Consequences of Adaptations • • • Some features of an organism might be consequences of other evolved characteristics. They do not increase reproductive success. Features likely arose as an unavoidable consequence of prior evolutionary change. Shaping Evolutionary Theory Mechanisms of Evolution • • Population genetics Hardy-Weinberg principle states that when allelic frequencies remain constant, a population is in genetic equilibrium. • This equation allows us to determine the equilibrium frequency of each genotype in the population. Homozygous dominant (p2) Heterozygous (2pq) Homozygous recessive (q2) • • • Genetic Drift • • A change in the allelic 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. 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. Bottleneck Occurs when a population declines to a very low number and then rebounds Gene Flow • Increases genetic variation within a population and reduces differences between populations Nonrandom Mating • Promotes inbreeding and could lead to a change in allelic proportions favoring individuals that are homozygous for particular traits Natural Selection • Acts to select the individuals that are best adapted for survival and reproduction Stabilizing selection operates to eliminate extreme expressions of a trait when the average expression leads to higher fitness. Directional selection makes an organism more fit. Disruptive selection is a process that splits a population into two groups. 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. Prezygotic isolation prevents reproduction by making fertilization unlikely. Prevents genotypes from entering a population’s gene pool through geographic, ecological, behavioral, or other differences Postzygotic isolation occurs when fertilization has occurred but a hybrid offspring Prevents offspring survival or reproduction cannot develop or reproduce Liger Allopatric Speciation A physical barrier divides one population into two or more populations. Abert squirrel Kaibab squirrel Sympatric Speciation • • A species evolves into a new species without a physical barrier. The ancestor species and the new species live side by side during the speciation process. 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 Follows large-scale extinction events South American Cichlids Coevolution • • • The relationship between two species might be so close that the evolution of one species affects the evolution of the other species. Mutualism Coevolutionary arms race Convergent Evolution • Unrelated species evolve similar traits even though they live in different parts of the world. Rate of Speciation • Evolution proceeds in small, gradual steps according to a theory called gradualism. • Punctuated equilibrium explains rapid spurts of genetic change causing species to diverge quickly.