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Transcript
Life on Earth: The Theory of Evolution What is a Theory Video Segment 1 https://www.youtube.com/watch?v=85di EXbJBIk&list=PL5270149AB732F0FB&i ndex=1 Origin of Life Before the 17th century people believed in a process called spontaneous generation. Living things could arise from non-living things. Why did they think that? If they would leave rotting meat out then maggot seem to appear so the meat must give rise to maggots. (NOT Exactly) Experiments In 1668, Redi proved spontaneous generation to be false Meat and Flies Spallanzani also preformed an experiment 2 broth flasks (boiled) Problem: what happens to bacteria when you cook them? 1800’s, Louis Pasteur modified Spallanzani’s experiment Used curved necked flask Earth’s History Earth is about 4.6 billion years old No usable oxygen. Anaerobic organisms. The fossil evidence says they were most likely prokaryotes Probably heterotrophs Some may have also been autotrophs Archaebacteria bacteria that uses chemosynthesis instead of photosynthesis We need More Oxygen Some relatives to cyanobacteria used photosynthesis more oxygen is formed. Some of this oxygen went into the upper atmosphere where it formed the ozone layer. The ozone layer helps protect the earth from ultraviolet radiation that can damage DNA More complex cells form So we have prokaryotes that are aerobic and are not to complex Endosymbiosis The small invaders would give rise to mitochondria and chloroplasts Mitochondria and chloroplast have their own circular DNA that is different from the cells DNA Possible explanations for the things that have been observed. ??? Lamarck’s explanation His hypothesis Similar species descended from a common ancestor His evidence Fossil records His reasoning Acquired trait are passed on to offspring Things passed on due to experience not genetic “The Inheritance of Acquired Characteristics” Example: A giraffe acquired its long neck because its ancestor stretched higher and higher into the trees to reach leaves, and that the animal’s increasingly lengthened neck was passed on to its offspring. Darwin and Wallace About 50 years later, two scientists, Charles Darwin and Alfred Wallace, both came up with the same idea: natural selection Natural selection: organisms that are best suited for their environment are able to reproduce hence passing on the favorable traits. Charles Darwin Darwin set sail on the H.M.S. Beagle (18311836) to survey the south seas (mainly South America and the Galapagos Islands) to collect plants and animals. On the Galapagos Islands, Darwin observed species that lived no where else in the world. These observations led Darwin to write a book. Video Segment 2 “Who is Charles Darwin” https://www.youtube.com/watch?v=vmphlb RhLu8&list=PL5270149AB732F0FB&index =2 Darwin’s Two Theories Descent with modification Newer forms appearing in the fossil record are really modified descendants of older species Modification by natural selection Describes how evolution occurs Environment affects populations, some organisms can cope and others cannot. Adapting results in a change in the genetic make-up of the population (selective advantage) Fitness is a single organisms contribution to change Natural Selection Individuals with favorable traits are more likely to leave more offspring better suited for their environment. Example: English peppered moth (Biston betularia) - light and dark phases Natural Selection 1. All species produce offspring at a faster rate than food supplies can increase. 2. Except for identical twins, no two individuals are exactly alike. 3. In each generation, more individuals are produced than can survive. 4. Individuals that possess certain traits have an advantage over those that do not. Natural Selection 5. Geographical isolation may lead to the formation of a new species. 6. The environment determines whether a trait is beneficial. 7. Traits are inherited and passed on to the next generation. 8. Over time, successful variations accumulate in a population, and a new species may appear. https://www.youtube.com/watch?v=ewtw_nZUIDQ&list=PL52701 49AB732F0FB&index=3 Darwin’s key idea: Natural Selection **Four tenants of natural selection** 1. Genetic Variation: Variety of traits exist. These variations are called alleles. Example: blue eyes, brown eyes. 2. Overproduction of offspring: Organisms produce more offspring than can survive 3. Struggle for existence (Survival of the fittest): Organisms compete over resources to survive and reproduce. Organisms best suit for environment survive to pass on genes. 4. Differential survival & reproduction: over time, traits of successful reproducers become more common Evidence of Evolution Biogeography – Plate Tectonics Fossil Record Adaptations Comparative Anatomy 1. 2. 3. 4. • • Vestigial Structures Homologous/Analogous structures 5. Comparative embryology 6. Molecular biology How does it work Video Segment #4: How Does Evolution Really Work? https://www.youtube.com/watch?v=xkw RTIKXaxg&index=4&list=PL5270149AB 732F0FB Biogeography Geographical distribution of species. Organisms tend to arise in areas where similar organisms lived in the past Comparative Anatomy: Structural similarities link related species Vestigial Structures Features that are not used by the organism but may have been useful to ancestors Example: In humans: tailbone, appendix In whales: pelvic bone and four chambered stomach In snakes: pelvic bone, limb bones Homologous structures Homologous: structures that are similar because of common ancestry and develop similarly Homologous and embryo Complete the homologous and embryo color sheet following the teacher directions. Comparative embryology Study of structures that appear during embryonic development. Molecular biology DNA and proteins (amino acids) Mutations are changes in the DNA. Gene flow is any movement of genes from one population to another. Sexual Reproduction Convergent Evolution Species from different evolutionary branches may come to resemble each other even though they are not closely related Example: 1. Ostrich (Africa) & Emus (Australia). 2. Sidewinder (Mojave Desert) & Horned Viper (Middle East Desert) 3. Sharks and Dolphins Divergent Evolution 2 or more species or related population become more and more dissimilar Can result in a new species Types: Adaptive radiation: related species evolve from a single ancestral species (Galapagos finches) Artificial selection: breeding organisms for specific trait (dogs) Writing Under your notes Write me a paragraph in detail describing what you have learned so far about evolution. We have done dot lab, checks lab, evidence of evolution, theory of evolution, lamark versus Darwin. Mechanisms of Change 1. Mutation A change in the DNA sequence. (1 in 100,000) leads to new traits. Some traits will be advantageous to the species. 2. Migration Movement of individuals form one population into another. Can alter the genetic characteristics of a population. Mechanisms of Change 3. Nonrandom Mating- controls the genes When individuals mate with one another more or less frequently: example inbreeding. 4. Selection Artificial Selection – individuals breed organisms for specific traits. Natural Selection environment dictates Which traits are needed to survive. Mechanisms of Change 5. Genetic Drift Random loss of alleles. Small population a person does not reproduce. Founder effect – one or a few individuals migrate and become an isolated population with distinct genotypes. The population splits due to migration events Bottle neck – restrictions in genetic variability due to flooding or natural disasters. The population splits due to natural disasters Speciation (How do we get a new species?) Usually involves successive change Local populations of a species become isolated and more specialized (adapted) Natural selection acts to keep them specialized (different from the larger population) Populations of a species must become reproductively isolated in order to develop into new species. Mechanisms of Change Complete the coloring sheet Gene Flow Be sure to read and highlight Color neatly Complete the coloring sheet Genetic Drift Be sure to read and highlight Color neatly