Transcript 15.1 Notes
I. Charles Darwin and Natural Selection A. In 1831 a scientist named Charles Darwin set sail on the H.M.S. Beagle. 1. The voyage lasted 5 years and covered S. America & the South Pacific. 1000 Km off the coast of South America OR 621 miles 2. He collected and studied organisms during his travels. B. The organisms he collected in the Galapagos islands were especially important. C. Darwin came to some conclusions: 1. Most organisms over-reproduce 2. Individuals struggle to survive (competition for food, shelter, mates, escaping predators). D. Darwin identified an organisms ability to survive as Natural Selection – a mechanism for change in a population of organisms. 1. Natural selection occurs when organisms with certain variations survive, reproduce, and pass their variations to the next generation. II. Adaptations A. Adaptation-a trait that makes a living thing able to survive in its surroundings. 1. Adaptations develop over several generations in a population. 2. One example of an adaptation is mimicry – where one organism resembles another organisms that could be harmful. On the next slide, Pick out which snake is poisonous and which one is not poisonous. Harmless kingsnake Harmful coral snake 3. Some organisms blend into the environment - camouflage Because well-camouflaged organisms are not easily found by predators, they survive to reproduce. III. Evidence for Evolution A. Fossils play an important role in evolutionary evidence. Camel Evolution Age Organism Skull and teeth Limb bones Paleocene 65 million years ago Eocene 54 million years ago Oligocene 33 million years ago Miocene 23 million years ago Present B. Anatomy also plays an important role in evolution. 1. Structural features with a common evolutionary origin are called homologous structures. i. Homologous structures can be similar in arrangement, in function, or in both. Whale forelimb Crocodile forelimb Bird wing 2. Another type of body feature that suggests an evolutionary relationship is a vestigial structure—a body structure in a present-day organism that no longer serves its original purpose, but was probably useful to an ancestor. 3. A structure becomes vestigial when the species no longer needs the feature for its original function, yet it is still inherited as part of the body plan for the species. i. Many organisms have vestigial structures. • Vestigial structures, such as pelvic bones in the baleen whale, are evidence of evolution because they show structural change over time. The appendix is a vestigial structure in humans. Ostridge and Emu wings are vestigial structures. 4. Body parts of organisms that do not have a common evolutionary origin but are similar in function are analogous structures. C. Embryology is another way to determine if two organisms are related. 1. An embryo is the earliest stage of growth and development of both plants and animals. 2. As an organism develops the embryos become more distinguishable. D. Biochemistry also provides evidence about relationships between organisms. 1. DNA comparisons offer the best evidence. Physiological adaptations can develop rapidly Non-resistant bacterium Antibiotic Resistant bacterium The bacteria in a population vary in their ability to resist antibiotics. When the population is exposed to an antibiotic, only the resistant bacteria survive. The resistant bacteria live and produce more resistant bacteria. Physiological adaptations can develop rapidly Non-resistant bacterium Antibiotic Resistant bacterium • Today, penicillin no longer affects as many species of bacteria because some species have evolved physiological adaptations to prevent being killed by penicillin.