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Source: donsmaps.com Chapter 17 and 18: Darwin’s Theory of Evolution Source: http://anthro.palomar.edu/evolve/evolve_2.htm Theory of Evolution Evolution: Gradual process (over millions of years!) by which modern organisms have descended from ancient ancestors Evolution is based on scientific facts, observations and hypotheses Proposed by Charles Darwin… let’s examine his voyage and data. Charles Darwin English naturalist Set sail on a 5 year cruise on the HMS Beagle in 1831 Source: http://anthro.palomar.edu/evolve/evolve_2.htm The Voyage At each stop, Darwin: Made biological and geological observations Collect plant and animal specimens Collected Fossils Darwin Observed A great deal of biodiversity! Vast number or plants & animals species lived at each location Each species seemed well adapt to its environment An intriguing geographic distribution of species Today we know that there are about 1.75 million species on the planet. This number only represents 1% of all species that ever lived on Earth! The Galapagos Islands: An Important Influence on Darwin Small group of Islands located 1000km west of South America The Islands had very different climates Darwin noticed that plants and animals varied noticeably from island to island. • Ex: Land Tortoises 14 different sub-species 4- extinct 1 almost extinct 9- living Source: www.thebestofecuador.com Darwin found the shell shape corresponds to the habitat Lonesome George Figure 15-3 Variations in Shell Shape (p. 371) Darwin’s Thoughts Where did all the animals come from? Where did humans come from? What about fossils? Has everything always been here? How old is the earth? Do plants ever change? What happened to all the dinosaurs? Darwin’s Proof Evidence of Evolution The Fossil Record Geographical Distribution Similarities • Embryology • Chemical Compounds • Body Structures The Fossil Record By comparing older fossils with younger fossils, evidence of change is clear. Geologic Time Scale Precambrian 4.6 bya-544 mya (life, eukaryotes) Paleozoic 543-245 mya (cambrian explosion) Mesozoic 245-67 mya Triassic: Mammals/dinosaurs appear Jurassic Cretaceous – radiation of species (spp) Cenozoic 66 mya to present (human era) Radiometric vs. Relative Dating ½ Life of Elements Decay Depths of Strata Geographic Distribution of Living Species Darwin discovered the existence of similar but unrelated species in different locations Darwin later realized the similar animals were products of different lines of evolutionary descent. Similarities in Early Development Let’s examine embryos In the late 1900’s many thought, embryos looked the same While that’s not exactly the case • Similar genes are at work in early development • As they grow the become more dissimilar • Differences caused by genes that have changed due to evolution Similarities in Early Development Similarities in Body Structure Embryos develop limbs that are structurally similar Evolutionary changes altered the structure and appearance based on their FUNCTION Why? They’re adapted to allow organisms to survive in their environment These structures are called Homologous Contrasting idea: Analogous Structures (suggest species evolution converged due to similar environments) Homologous Structures Analagous Structures Vestigial Organs Organs that have no or little purpose. Evolution has lead to adaptations that suit particular organisms Similarities in Chemical Compounds All organisms use DNA and/or RNA Many organisms have similar proteins The more closely related two species are, the more their chemical properties resemble each other. Darwin’s ideas were heavily influenced the ideas of the time Early Explanations of Change James Hutton (1726-1797) Thought that geological changes were the result of gradual change over a long period of time Earth is 4.6 billion years old! Significant: • many at and before his time believed the earth was only a few thousand years old. Early Explanations of Change Charles Lyell (1797-1875) Developed the theory of uniformitarianism “the present is key to the past” The current geologic processes have shaped the earth’s topography. Geologic processes take a long time! (millions of years!) Early Explanations of Change Jean Baptiste Lamarck (1744-1829) Proposed a theory of evolution based on selective use or disuse of traits • All organisms have a tendency toward perfection Organisms are continually changing and acquiring features that help them • Use and Disuse Organisms can alter the size/shape of a particular appendage by using it in a new way Inheritance of Acquired Traits modifications could be passed on to offspring giraffes who developed longer necks from stretching could pass these long necks onto their offspring Early Explanations of Change Jean Baptiste Lamarck (1744-1829) Lamarck did not know how traits were acquired and passed on. His hypothesis had many flaws. His ideas helped ideas about adaptation paved the way for Darwin’s theory Early Explanations of Change Thomas Malthus (1766-1834) Was an economist Notice babies were being born faster than people were dying. Figured, sooner or later living space and food supplies would be in short supply Events such as famine, war and disease would limit population growth Darwin would later apply this idea to plants and animals Darwin Presents His Case Darwin reflected on his findings for many years after returning home. He wrote about his theories in, On the Origin of Species. Published in 1859 23 years after the voyage of the Beagle http://www.pbs.org/wgbh/evolution/educators/teachstud s/svideos.html Inherited Variation vs. Artificial Selection Variations: Different forms of alleles for a trait Inherited Variations Traits passed on from parent to offspring Artificial Selection (ex. dog breeding) Humans select useful variations from naturally occurring traits Selective breeding practices Evolution by Natural Selection The Struggle for Existence Darwin thought nature used an “artificial selection process” Members of each species compete for resources Natural Selection Processes in nature that over time results in only the survival of the fittest species Results in changes of inheritable characteristics of a population. Changes increase a species’ fitness in its environment Survival of the Fittest Fitness Ability of an individual to survive and reproduce. Fitness is a result of adaptations Adaptation Physical and behavioral traits that allow an organism to survive in its environment Darwin Concluded: Over long periods of time, natural selection produces organisms that have different Structures Niches Habitats Species descended with modifications from a common ancestor. Implies all living things are related to one another This principle is known as common descent Darwin’s Finches Similarities can be explained with Darwin’s theory: Living organisms evolved with gradual modification of earlier forms of an ancestor with common descent. Let’s Look at an Example… In pre-industrial England, there was a species of moth called the Peppered Moth (Biston betularia) Almost all peppered moths were gray with dark flecks Rarely were they black The Peppered Moth The peppered moth tend to rest on tree trunks during the day The gray moth were well camouflaged on the gray tree trunks Black moths stand out and are easy targets for birds. The Peppered Moth Now, turn to England during Industrial Times… Pollution from the factories turned tree trunks black with soot. Now, the black moths were camouflaged on the trees. The Peppered Moth The black moths had a better chance of survival They had a higher fitness After many moth generations, almost all the months in industrial areas were black The Peppered Moth Black coloration is an adaptation to an environment with black tree trunks In an industrial environment, black moths survive to reproduce better than gray moths. Therefore, their genes are passed on to future generations