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Evolution I. Origins of Life on Earth A. Oparin Model of Life 1. In 1924, Russian scientist Aleksander Oparin proposed that Earth is approximately 4-5 billion years old and that the ancient atmosphere contained: a. b. c. d. ammonia (NH3) water (H2O) vapor methane (CH4) hydrogen (H2) Which important gas(es) is/are missing? 2. Energy from the sun, lightning and heat from the earth broke apart these molecules. 3. The atoms randomly bonded together to form amino acids, sugars and fatty acids, which accumulated in the oceans. What are proteins made of? 4. Over millions of years these organic compounds combined to form simple cells that filled the Earth’s primordial oceans. B. Miller & Urey’s Experiment 1. In 1953, Stanley Miller and Harold Urey showed that you can make organic compounds from inorganic molecules. 2. The experiment: a. Miller electrocuted a mixture of water vapor, methane, ammonia and hydrogen gas. b. He collected the liquid and found amino acids, simple sugars and simple fats! c. However, as of today, no one has produced a living cell from nonliving materials. Miller & Urey’s Experiment (1953) II. General Info A. Evolution means “change over time” B. Process by which modern organisms have descended from Earth’s earliest forms of life C. It is a scientific theory What is a scientific theory? It is a well-supported, testable explanation of events that occur in the natural world Just a Theory? Movie D. Foundation of modern biology that unifies many different branches of science III. Darwin’s Theory of Evolution A. Background Info 1. Most Europeans in the 1700-1800’s believed: a. Earth was only several thousand years old b. Since their creation, neither plants nor animals had changed Approximately how old is Earth? B. Ideas that Shaped Darwin’s Thinking 1. In 1795, James Hutton proposed that layers of rock form over millions of years; therefore Earth had to be more a few 1000 years old 2. In 1841, Thomas Malthus predicted in his Essay on the Principle of Population that the human population will grow faster than the space and food needed to sustain it What happens to populations of organisms that exceed their resource limits? 3. Hypothesis of Acquired Traits a. In 1809, Jean Baptiste de Lamarck proposed that traits developed during a parent’s lifetime are inherited by their offspring Is this a supported hypothesis? My, How You’ve Changed! Prior to the 1800s, life scientists knew that living things changed over generations. They just didn’t know how these changes were brought about. 1. Make two columns: Inherited Traits Acquired Traits 2. 1st column, list the traits that you believe you have always had. Ex: brown eyes, curly hair 3. 2nd column, list your acquired traits. Ex: playing a musical instrument 4. Which of the items in your lists do you think you might pass on to your children? 4. In 1830, Charles Lyell explained in his book Principles of Geology how geological events (volcanoes, earthquakes) build up or tear down the Earth over millions of years a) Explains how marine fossils can end up on mountain tops C. Evolution by Natural Selection 1. Voyage Around the World a. In 1831, Charles Darwin set sail from England on the HMS Beagle for a voyage around the world Voyage of the HMS Beagle b. As the ship’s naturalist, Darwin recorded observations and collected specimens of the many plant and animals species he saw c. Galapagos Islands i. ii. Group of islands 1,000 km off the coast of Central and S. America that are close together but have very different climates and an amazing variety of species (iguanas, finches, tortoises) Diverse animals and plants seemed very well suited to their island’s environment iii. Beak shape of each species of Galapagos finch is related to its eating habit iv. Based on his observations, Darwin hypothesized that the Galapagos plant and animal species evolved from ancestors from Central and S. America 2. On the Origin of Species (book) a. 1859, Darwin published his findings b. Species are not perfect and unchanging c. Proposed a mechanism for evolution called natural selection organisms with traits best suited to their environment are more likely to survive and reproduce (“survival of the fittest”) d. Survival of the fittest i. Fitness = ability of an organism to survive and reproduce in its environment ii. Adaptation = inherited characteristic that increases the chance of survival (write examples) iii. Over time, natural selection results in changes in the inherited traits of a population, increasing that species’ fitness. Natural Selection Movie 3. Summary of Darwin’s Theory a. Organisms produce more offspring that can survive (think mice, bunnies, etc) b. Individual organisms of the same species differ, and some of this variation is inheritable. Homo sapiens Drosophila polymorpha i. Today, we know these variations are the result of mutations. ii. Mutations occur by random chance and if favorable, it will be inherited by organism’s offspring (e.g. Peppered moths, antibiotic resistant bacteria or insecticide resistant insects) c. Organisms struggle to survive Why? i. Individuals of each species compete for resources (food, space, mate, etc) d. Species alive today have descended with modification from ancestral species of the past. This process unites all organisms on earth into a single tree of life. A. IV. Evidence for evolution The Fossil Record – provides evidence about the history of life on Earth 1. Fossils are preserved impressions or physical remains of an organism that once lived. Petrification Impression Cast/Mold Amber Cast/Molds Baby mammoth found frozen in Russia in 2007 Iceman found frozen in the Alps, Italy in 1991 2. Fossils occur in a particular order; simpler forms existed before more complex forms (e.g. the oldest known fossils are prokaryotes) 3. Fossil dating techniques a. Relative Dating - layering of sediment results in the oldest and simplest fossils usually further down b. Absolute/Radiometric Dating i. Some rocks contain elements that are radioactive and will decay (break down) at a constant rate over time ii. Half-life = length of time required for half of the radioactive atoms in a sample to decay iii. Scientists can calculate the age of a sample by measuring remaining amount of radioactive isotopes like carbon14 4. Transitional Forms a. Intermediate forms of life appearing in the fossil record that are "in-between" existing types of organisms found today or in the past b. Many examples of transitional forms exist in the fossil record The Aetiocetus nostril placement is an intermediate form between the ancestral form Pakicetus and the modern beluga. Evolution of Horse Feet sampling of horse fossils leading to modern horses the diagram shows transitional stages whereby the four-toed foot became the singletoed foot of Equus shows the reduction of toes through time Archaeoptryx A model of Tiktaalik roseae, a fish in transition to becoming a land animal. Early transitional form between fish and amphibians. Limb Evolution How do we know evolution happens? MOVIE B. Biogeography 1. Geographical distribution of species 2. Species living on different continents who descended from the same ancestor, look slightly different because they were exposed to different ecological conditions (e.g. armadillos and anteaters, lions and tigers) 3. Consistent with plate tectonics C. Comparative Anatomy 1. Homologous structures – made of the same types of bones, but the function or structure may be different a. Example: basic bones in the arms of a human, wings of a bird and fins of a whale. 2. Vestigial Structuresinternal structures that serve no known purpose. 3. Atavism - rare reappearance of a lost characteristic specific to an evolutionary ancestor (gene is turned back on) a. Ex: whales with legs, human babies with true tails The hind-flippers of a bottlenose dolphin found in Japanese coastal waters in 2006. Yellow arrows indicate the location of a well-formed atavistic set of hind limbs. (photos from the Taiji Whaling D. Comparative Embryology- closely related organisms pass through similar stages as embryos -> shows common ancestry E. DNA 1. Scientists can compare the DNA of different species to determine their relatedness 2. Closer similarities means more likely to have a common ancestor 3. Example: a human’s DNA is ~ 97% similar to that of a chimpanzee. Genetic relatedness Number of amino acid differences in hemoglobin