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There is a Great Diversity of Organisms on Planet Earth……….why? What Best Explains Diversity? I. Special Creation Aristotle to Darwin ~350 BC to 1800s II. Evolution Darwin to Present (A) Each organism originated independently. (A) All organisms originated from common ancestors. (B) Since the time of creation, each organism has remained the same. (B) Organisms have and continue to change over time. (C) All organisms were created recently. (C) Evolution of organisms began 3.7 billion years ago For a more details concerning the History of Evolutionary Thought: http://www.ucmp.berkeley.edu/history/evolution.html For information about the Evolution/Creationist Controversy: http://www.talkorigins.org/ National Center for Science Education: http://www.natcenscied.org/ Jean-Baptiste de Lamarck (1744-1829) First Theory of Evolution Transformational Evolution Humans Mammals Amphibians Scale Of Nature Fish Insects Jellyfish Zooplankton Pond Scum Time Lamarck : • Believed in inheritance of acquired characteristics (acquired during life) Parents Parents Change During Lifetime Change Inherited by Offspring Parents Change During Lifetime Change Inherited by Offspring Parents Change During Lifetime Grows up Among Short Trees Inheritance of Acquired Characteristics Two Sibling Giraffe’s Grows up Among Tall Trees: Longer neck Importance of Lamarck’s Theory • Recognized that life forms were connected • Recognized that there is variation in traits • Recognized that evolution requires time (Earth is Old). • Recognized that inheritance is an important aspect of adaptation Darwin (1809-1882) “On the Origins by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle of Life” • Two Major Ideas: – Common Descent All living and extinct species descended from one or a few common ancestors. • aka: Macroevolution – Adaptation occurs by Natural Selection The characteristics of organisms change through time as a result of natural selection. • aka: Microevolution The only figure in “On the Origins….” Darwin’s Idea of Common Decent Implies: (1) Branching evolution (2) That species accumulate differences over time Genus 1 Species 1 Species 2 Genus 2 Species 1 Extinction Differences Accumulate Over Time Species 2 Species 3 Species 5 Species 4 Systematists Study Differences Among Species to Reconstruct Phylogeny (i.e. Phylogeny = Genealogy of Species) http://phylogeny.arizona.edu/tree/ Evolution by Natural Selection What is adaptation? Process of genetic change whereby individuals of a population become better suited to their environment Evolution After Darwin Most accepted idea of common descent, but not natural selection. Competing theories were proposed: Orthogenesis: variation in the characteristics of organisms is channeled in pre-determined directions. Macromutation: downplayed the importance of continuous variation and stressed discrete variation. Thought evolution only depended upon mutation rate. The Modern Synthesis (1930’s - 40’s) Synthesis of ideas/concepts among geneticists, natural historians, and evolutionary biologists that modern evolutionary biology is built upon. Emphasized the co-action of random mutation, selection, genetic drift, and gene flow in microevolution. Emphasized that these evolutionary processes were sufficient to account for macroevolutionary trends. MS concepts from Laboratory Genetics 1. P=G+E Phenotype = Genotype + Environment 2. Environmental effects on phenotype are not inherited 3. Heredity is based on particles (genes). They retain identity and do not blend. They give rise to continuous and discrete variation. 4. Genes mutate at relatively low rates. Recombination is an important aspect of evolution. 5. Environmental factors can influence mutation rates but do not yield specific mutations that are seemingly the best for surviving in a particular environment. MS concepts from Population Genetics 1. Selection can alter populations beyond the original range of variation by restructuring genomes through recombination, and thus give rise to new phenotypes. 2. Natural populations are genetically variable. 3. Populations of a species in different geographic areas may differ in genetically based characteristics. Genotypic frequencies may vary among populations. Often differences are adaptive, and thus a product of natural selection. 4. Experimental crosses among populations or species show that most characteristics have a genetic basis, and most have a complex or polygenic basis. This suggests that evolution may occur through small steps. MS concepts from Population Genetics (cont.) 5. Organisms are not necessarily different species if they exhibit different characteristics. A species is a collection of populations that interbreed, and is thus characterized by a common gene pool. (i.e. Biological Species Concept) 6. However, there is a continuum of differences among populations and even in the degree of reproductive isolation. There are also a continuum of differences observed among species, or genera, or higher taxonomic classifications. This provides evidence that an ancestral species differentiates into two or more different species. 7. Speciation generally occurs through the genetic differentiation of geographically separated populations. This creates isolation and prevents gene flow. MS concepts from Systematics/Paleontology 1. The fossil record has gaps among quite different organisms. This reflects the incompleteness of the fossil record. However, there are gradations or intermediates that fill some gaps. It seems likely that the evolution of large differences occurs through many small steps that are fixed over very long time periods. 2. All observations in the fossil record are consistent with evolutionary principles and there is no need to invoke NonDarwinian mechanisms (orthogenesis, major-mutational origins, Lamarckian evolution).