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Evolutionary Thought Theories of Evolution Questions about the world that started to set the stage for modern evolutionary thought GEOLOGY Age of earth? Changing earth? POPULATIONS Competition? Change over time? Extinction of species? GEOLOGY Hutton and Lyell (geologists) James Hutton (1785) hypothesized earth to be very old when he examined geologic features such as rock layers and erosion Charles Lyell (1833) Hypothesized that complex geologic processes like erosion, volcanoes, etc. shaped the earth as we currently see it. CONCLUSIONS: EARTH IS VERY VERY OLD! Today’s best guess??? 4.6 Billion Years 1809:Lamarck’s Theory Use and Disuse: Body parts that are used more grow stronger and bigger. Body parts not used will deteriorate. Inheritance of Acquired Characteristics: Physical changes that occur in an organism are inherited by its offspring. Example: Giraffe’s neck gets longer as it stretches to reach food in trees. But was Lamarck correct? NO According to genetics… only variations that occur in gametes the genes of ____________ are passed to offspring. variations that occur in somatic cells (body cells) _____________ are NOT inherited. Thomas Malthus (1798) Observed human population growth will eventually hit a limit due to living space and available food. Darwin would later apply this to all organisms where these limits result in competition. While Lamarck's reasoning behind why change happened was flawed, Lamarck and Malthus both greatly influenced the thinking of Mr. Charles Darwin. Charles Darwin English scientist born in 1809 1831 famous voyage around world on HMS Beagle where he examined numerous different types of animals and the wide diversity of life he found Noted that organisms seemed to be uniquely adapted to their environments Galapagos Similar organisms on different islands had unique characteristics that suited their specific habitat On the Origin of Species Published 1859 Summarized his ideas on causes of speciation Darwin's On the Origin of Species by Means of Natural Selection, made several points that had major impact on nineteenth-century thought: Main Principles of NATURAL SELECTION I. Competition. II. Survival of the fittest III. Descent with modification Natural Selection: Competition Members of the same species are in competition with each other for food and space. Over production: In a population, more offspring are produced than can survive. “Struggle for existence” Individuals with traits that give them an advantage make better competitors. Natural Selection: Survival of the Fittest Variation: There is variation within a population and variations are inherited. Adaptation: Traits that are favorable and improve the organism’s ability to function and reproduce. Survivors pass on their variations. Therefore a larger proportion in the next generation will have those variations. “Fitness” in evolution is a measure of an individual’s ability to survive and pass on genes (reproduce!) measure of an individual’s genetic contribution to the next generation. Natural Selection: Descent with Modification As new desirable characteristics become established within a population, the species as a whole changes over long periods of time. Evolution is the development of new organisms from preexisting organisms over time. Speciation: Over time, small changes accumulate and populations change. Species: a group of organisms that can mate and produce fertile offspring. Sometimes, two populations diverge (change differently) and become two separate species. Each of the Hawaiian honeycreeper species has a bill specialized for eating certain foods. Scientists suggest that all 23 honeycreeper species apparently arose from a single species that migrated to Hawaii. Lamarck vs Darwin Lamarck Use / disuse Transmission of acquired characteristics Darwin Variation Inheritance Increasing complexity Differential survival No extinction Extinction Principle of Common Descent All species (living and extinct) have evolved from common ancestors for a very long time. Evidence of Evolution • • • • • • • Fossil Record Geographic Distribution Transitional Species Comparative Anatomy Vestigial Organs Comparative Embryology Comparative Biochemistry Fossil Record Preserved remain of ancient life in rock support change over time. Fossils found in lower levels of rock older than ones above. (relative age) Majority of species (over 99%) that have existed on this planet are extinct! Very hard for an organism to become a fossil. How is the age of fossils and rocks determined? Radiometric dating – using half-lives of radioactive isotopes Radioactive isotopes decay at a constant rate Half Life length of time for ½ of an isotope to decay Ex. Carbon-14 decays to Nitrogen-14 Half-life = 5,730 years Carbon 14 can only be uses to date fossils less than 50,000 years old! Geographic Distribution Biogeography study of the distribution of plants and animals throughout the world Some fossils found on different continents nearly identical supporting movement of continents. There are patterns in how species occur geographically, based on such factors as where they evolved, how far they dispersed, and how changes in the Earth affected their distribution. Transitional Species While theoretically, all species are “transitional”, we use this term to classify certain species as almost “stepping stones” from one type of organism to another. Ex. Fish Amphibian Homologous Structures (Comparative Anatomy) Scientists note similarities among physiology of organisms Morphologically similar structures that perform different functions are called homologous structures. Analogous Structures Serve similar function but have a much different structure Ex. Insect wing and bird wing Ex. Squid eye and human eye Ex. Whale fin and fish fin Vestigial Organs Rudimentary structures that are of marginal or no use to an organism, or structures in which the shared form appears to be inefficient. Examples Skeletons of some snakes retain the vestiges of pelvic girdle and leg bones of walking ancestors. Some blind, cave-dwelling fish have eyesockets but no eyes. Comparative Embryology closely related organisms go through similar stages during their embryonic development Biochemical Similarities What we all use DNA ATP (energy molecule) similar enzymes, same codons for protein synthesis same 20 amino acids etc. Remember, at the cell level we are very close to most other eukaryotic organisms! Evolution in Action All inheritable physical traits that appear in an organisms can be looked at as changes in an organism’s genetics Darwin did not understand genetics and therefore could not explain how traits were passed down through generations. We now can apply our understanding of genetics and apply them to evolutionary theory. Phylogeny the connections between all groups of organisms as understood by ancestor/descendant relationships. Express relationships using a CLADOGRAM Cladogram Gene Pool is combined genetic information of all the members of a particular population In a given gene pool, there will typically be two or more different alleles for a given gene. Relative Frequency – number of times that an allele occurs in a gene pool compared with the number of times other alleles occur. We can oftentimes see that different alleles have different frequencies in different parts of the world. Why do you think this is so? Ex. Frequency of B allele for blood type Genetic Change basis of Evolution Natural selection acts on phenotypes NOT genotypes, however, this process determines the relative frequencies of alleles. Ex. Sickle cell anemia Phenotype (blood cell shape) because heterozygous individuals are resistant to malaria. Malaria resistance causes sickle-cell allele to be selected for in the population. Mechanisms of Evolution Introduce new Alleles Sources of Genetic Variation Mutations Sexual Reproduction External factors affect the allele frequency Remember, it is mutation that proposes and selection that disposes What can change allele frequencies besides natural selection? Genetic Drift Evolutionary Change can also happen without natural selection In large populations, the laws of probability help predict allele frequencies. In smaller populations random change in allele frequency (genetic drift) may occur. Chance occurrences may increase/decrease frequency of alleles Mass Extinctions There have at least 5 mass extinctions. Permian – 250 mya, over 90% of marine and terrestrial species disappeared; maybe due to volcanoes, Pangeae, glaciation Cretaceous – 65 mya; ½ marine and many terrestrial forms, including dinosaurs; due to environmental changes or asteroids hitting the earth Genetic Equilibrium In order for there to be no evolution (allele frequencies remain constant) five conditions must be met; Random mating Large population No migration in or out of population No mutations No natural selection Is this ever the case? TWEEKING DARWINISM Traditionally, it was believed that evolution happened in small steps over long period of time. This is called gradualism More recently, scientists like Stephen Gould, proposed the idea of punctuated equilibrium which is that a species may remain relatively stable with sudden periods of rapid evolution due to some environmental factor. CHANGES IN SPURTS! What is a theory? Evolution is an observable fact (bird beak size changing, antibiotic resistance in bacteria, etc.) but the term theory allows it to grow and develop. Misconceptions About Evolution