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Transcript
5.4 - EVOLUTION “Nothing in biology makes sense except in the light of evolution.” Theodosius Dobzhansky, 1973 IB Biology Stephen Hawking “A good theory will describe a large range of phenomena on the basis of a few simple postulates and will make definite predictions that can be tested. If the predictions agree with the observations, the theory survives that test, though it can never be proved to be correct. On the other hand, if the observations disagree with the predictions, one has to discard or modify the theory.” Source: The Universe In A Nutshell Just a theory – http://www.youtube.com/watch?v=85diEXbJBIk What is Evolution? Evolution is the cumulative change in the heritable characteristics of populations that occurs over successive generations Who can evolve? Individuals cannot evolve! ◦ Individuals cannot change their genes. Populations are the smallest unit that can evolve. ◦ Populations can have a shift in their gene pool. Why would populations evolve? •So that a population becomes better suited to its habitats. •Increased survival •Better chance of passing on characteristics to offspring. •Takes place over many generations. How does a population evolve? A shift in the gene pool so that a higher ratio of individuals have a particular adaptation. Adaptation ◦ a particular structure, physiology or behaviour that helps an organism survive and reproduce in a particular environment. e.g. camouflage, superb sense of smell, bill shape Lamark Theory of acquired characteristics Lamark said organisms acquired traits by using their bodies in new ways These new characteristics were passed to offspring Lamark was totally wrong! What did Darwin’s Travels reveal? Origin of the Species “can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection.” The diversity of living species was far greater than anyone had previously known!! These observations led him to develop the theory of evolution by Natural Selection!! Who was Darwin? Charles Darwin http://www.youtube.com/watch?v=vmphl bRhLu8&list=PL0DE312300D53EB93 How did tortoises and birds differ among the islands of the Galapagos? Each island had its own type of tortoises and birds that were clearly different from other islands How 1 finch became 13 distinct species? Darwin's finches share similar size, coloration, and habits. Their salient difference is in the size and shape of their beak. Once on the islands, the various species established themselves and determined territories. Evolution then set in and many unique species, of finches, resulted. These finches probably descended from one type of ancestor and then, due to isolation and through chance, different climates and natural forces such as food availability and type, they evolved into thirteen different types of finches. The process of their evolution would probably have begun with immigrants from the mainland. As they dispersed to different islands, new populations would be formed. Every time these satellite populations dispersed, there would be greater difference between the individual species. Natural Selection & Descent with Modification The traits that help an organism survive in a particular environment are “selected” in natural selection Each living species has descended with changes from other species over time Natural Selection and Species Fitness Overtime, natural selection results in changes in the inherited characteristics of a population. These changes increase a species fitness (survival rate) Those that survive, reproduce and pass on their genes. These are the genes that persist in the population. How does evolution really happen? http://www.youtube.com/watch? v=xkwRTIKXaxg Summary of Natural Selection Individuals within a species vary in many ways Some of this variability is heritable Every generation produces far more offspring than can survive Members of the same species compete Individuals with favourable variations are more likely to survive As these individuals contribute proportionately more offspring to succeeding generations, the favourable variations will become more common. Species alive today are descended with modifications from common ancestors Example of a population that evolved: Industrial Melanism in Peppered moths in England Evolution is a Theory – Just like Gravity! Evolution is a well supported explanation of phenomena that have occurred in the natural world • A theory in science is a well tested hypothesis, not just a guess • How do we know evolution happens? http://www.youtube.com/watch?v=ewtw _nZUIDQ Evidence of Evolution Fossil Record provides evidence that living things have evolved Fossils show the history of life on earth and how different groups of organisms have changed over time Whales evolved from landdwelling mammals (Whales Evolution) http://www.youtube.com/watch?v=8cn0kf8mhS4 Evolution - giant whales - BBC science http://www.youtube.com/watch?v=xCx-nwkj8fU Carbon-14 Dating http://www.youtube.com/watch?v=phZeE7Att_s Homologous Body Structures ◦ ◦ ◦ ◦ Structures that have different mature forms but develop from the same embryonic tissues Homology = Same structure, different function e.g. Wing of bat, human arm, leg of horse Analogy = Different structural origin, same function E.g. Wing of bat, wing of bird Turtle Alligator Bird Homologous Body Structures Vestigial Organs traces of homologous organs in other species Organ that serves no useful function ◦ e.g. Appendix, wisdom teeth, and tailbone in Humans ◦ Pelvic Bones in whales ◦ Hind leg bones in snakes ◦ Dew claw in dogs Embryology Similarities in Embryology In their early stages of development, chickens, turtles and rats look similar, providing evidence that they shared a common ancestry. Artificial Selection and Selective Breeding nature provides variation, humans select variations that are useful. Example - a farmer breeds only his best livestock Most domesticated animals are selectively bread Review Crash course – Natural Selection http://www.youtube.com/watch?v=aTftyFboC_M Crash course – evolulution http://www.youtube.com/watch?v=P3GagfbA2vo