Ch. 15 The Theory of Evolution 15.1 Natural Selection and the Evidence for Evolution A. Charles Darwin and Natural Selection – evolution is the ______________________________ ____________________________________ Charles Darwin (1809-1882) helped develop this theory. 1. ______________ shape ideas about evolution – paleontologists study fossils to learn about extinct organisms and determine any _______________________ with living species. 2. Darwin on HMS Beagle – at age 21, he took a job as a Naturalist on a boat that went to South America and the ______________ Islands. 3. ______________ in the Galapagos - While there, he noticed that animals on the mainland looked and behaved differently than animals on the island. This led him to develop his theory of evolution based on natural selection. 4. Darwin’ natural selection – ________ concepts explaining a mechanism for change in populations 1. In any population, _________ ______________ are produced than can survive. Ex: white moths outnumbered dark moths before the industrial revolution 2. ______________ exist within any population. Ex: light moths blended into tree bark 3. Some of these variations are _________ Ex: Soot turned tree bark black and dark moths blended in better 4. Those with favorable variations are better able to ______________ and ____________________. Ex: After, dark outnumbered white B. Adaptations for Evolution – _______________________________________________________ _____________________________________ which make an organism more suitable for survival 1. Structural adaptations arise over time – for a ____________ in the genetic code to cause a change in the population, the organism must be able to ______________ and _______________. Most mutation are harmful and cause death. For example, Some scientists believe that mole rats have lost their genetic ability for sight or even some animals have randomly mutated to mimic other organisms. a). ________________________ – a structural adaptation that enables one species to resemble another b). _____________________– an adaptation that enables a species to blend into its environment 2. Physiological adaptations can develop rapidly – some antibiotics are not as effective as they once were. Ex: penicillin does not have the effect that it used to C. Other evidences for Evolution – 1. ________________ – Paleontologist look to the fossil record to find transitional forms of organisms. They do not have intermediate forms for most species. The fossil record is incomplete 2. ________________ – similar anatomical structures are thought of as evidence of evolution from a common ancestor. Ex: forelimbs of vertebrates a). ________________ ________________ – structures similar in arrangement, function, or both b). ________________ ________________ – share a similar function but no common ancestor c). ________________ ________________ – structure that may have once function but currently does not. Ex: flightless birds, 3. __________________________– similarities between early stages of life 4. ________________________– DNA evidence shows that living organisms use nucleic acid to hold genetic information. DNA sequences can show how closely organisms are related. 15.2 Mechanisms for Evolution A. Population Genetics and Evolution– the gene pool determines the traits of a population 1. Populations, not individuals, evolve – characteristics acquired in an individuals life are not passed on to their offspring. ___________________________________________________________ can bring change to future generations a). ________________ ________________ – all the alleles of a populations genes b). ________________ ________________ – the percentage of any specific allele in the gene pool c). ________________ ________________ – a population in which the frequency of alleles remains the same over generations 2. Changes in genetic equilibrium – a population that is in genetic equilibrium in not evolving. There are 4 major causes for change in a population. a. Most mutations result in death or a disorder but some scientists think they could help an organism survive and reproduce b. The alteration of allelic frequencies by chance events. Changes in small, isolated gene pools Ex: 6 fingered Amish c. Immigration and emigration bringing new genes to population d. Survival of the fittest 3. Natural Selection acts on _________________________ – there are three different types of natural selection that act on variation: stabilizing (most common), directional and disruptive. a). natural selection that favors average individuals in a population Ex: human birth weight: too small and can’t survive on its own, too large and can’t fit through the birth canal b). natural selection that favors one extreme variation for a trait Ex: selection of dark peppered moths after the industrial revolution turned the lichen on trees dark c). Natural selection that favors individuals on either extreme of a trait’s variaiton Ex: mostly theoretical examples exist. Possibly Darwin’s finches who populated the islands vs. the mainland B. The Evolution of Species – evolution is the change in a species over time. Mutation, genetic drift, gene flow and natural selection can change a gene pool over time. These are examples of _____________________________. ________________________________ would be the theory of all life evolving from a single celled organism over long periods of time to all the kingdoms of life (Bacteria, Protist, Fungi, Plant, and Animal). The evolution of a new species is called speciation a). _______________________- occurs when members of similar populations no longer interbreed to produce fertile offspring within their natural environment. 1. Physical barriers can prevent interbreeding – water, mountains, volcanoes, storms… a). _______________________ _______________________ – occurs whenever a physical barrier divides a population 2. Reproductive isolation can result in speciation – as a population becomes increasingly distinct, reproductive isolation can arise a). ________________ ________________ – occurs when formerly interbreeding organisms can no longer mate and produce fertile offspring Ex: wood frogs usually breed in late March/early April while leopard frogs usually breed in mid-April 3. A change in chromosome numbers and speciation – ________________________________ _____________________ can result in polyploid individuals a). ___________________ – any species with a multiple of the normal set of chromosomes. Ex: many flowering plants, wheat, cotton, apples, bananas 4. Speciation can occur quickly or slowly – Scientists once argued that evolution occurs at a slow rate and that adaptive changes gradually accumulated over time in populations. a). ________________ – is the idea that species originate through a gradual change of adaptations Ex: camel fossils b). ________________ ________________ – this hypothesis argues that speciation occurs relatively quickly, in rapid bursts (10,000 years) with long periods of genetic equilibrium in between Ex: elephant fossils C. Patterns of Evolution – natural selection is an important agent for change 1. Diversity in new environments – geographically isolated places (ex: Galapagos islands) decreases the size of the gene pool and can lead to the microevolution of a species. Ex: Hawaiian honey creepers. Adaptive radiation is a type of divergent evolution that usually stems from a change in the environmental conditions (storms, fire, flood, natural disaster…) a). ________________ ________________ – when an ancestral species evolves into an array of species to fit a number of diverse habitats b). ________________ ________________ – the pattern of evolution in which species that once were similar to an ancestral species diverge, or become increasingly distinct. 2. Different species can look alike – occurs when unrelated species occupy similar environments in different parts of the world and share similar pressures of natural selection a). ________________ ________________ – a pattern of evolution in which distantly related organisms evolve similar traits Ex: Euphorbia tree (Africa) and the organ pipe cactus (N. and S. America)