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Transcript
Natural Selection The Mechanism of Evolution Variation and Adaptation Species consists of organisms that can produce healthy fertile offspring. Variation is defined as the differences between individual members of a population. The unique attributes of each organism. Variations w/in a Population Variations are the things that make organisms different from one another For Homo sapiens variation could be…….? Hair Color Height Eye color Inuit (Eskimos) have a stocky build. Less surface area to volume to conserve heat. Ethiopians: tall and skinny more surface area to volume (this allows for cooling of the body). Both are of the species Homo sapiens, but they are different variations of the species. They have evolved to suit their habitat Sources of Variation Mutation Beneficial - organism more likely to survive and reproduce Deleterious - organism more likely to die before reproduction Recombination Fusion of gametes Meiosis Crossing over Adaptation An adaptation is an inherited trait that increases a population’s chances of survival and reproduction in a particular environment. Ability to make tools The toxic slime of the Rough Skin Newt The Anteaters tongue and snout Theories of Change Charles Darwin random generational variation with environmental pressure over time causes change Bonnot theorized that periodically all life was destroyed by natural disasters. Lamarck 1. organisms strive to improve 2. use it or lose it 3. modifications are inherited Natural Selection Proposed by Charles Darwin: 1. There is variation within the population. 2. Some variations are good. 3. Not all offspring survive. 4. The individuals that survive and reproduce are those with GOOD variations. Factors Influencing Darwin 1. 2. 3. 4. Charles Lyell - who believed the earth changed slowly and uniformly Animal breeding practices – how we have bred animals for generations to get the traits that we want. Thomas Malthus - who studied human populations and the factors that influenced them Alfred Wallace - who independently reached the same conclusions as Darwin Natural Selection Says According to Natural Selection, the most successful individuals are those that grow up to have offspring that grow up to have offspring. Natural Selection is more of a measure of reproductive success and who leaves the greatest genetic contribution to the population. Fitness What is “Survival of the fittest”? The fittest individual grows up to have the most offspring that grow up to have offspring. Fitness is a measure of reproductive success. Punctuated Equilibrium & Gradualism Gradualism – small genetic changes act to change populations slowly over time. Eventually two new populations form. Punctuated Equilibrium – populations remain genetically stable for long periods, which are punctuated by periods of rapid genetic change (Adaptive Radiation) Fossil evidence provides more support of the theory of punctuated equilibrium than it does for gradualism. Evidence Punctuated Equilibrium 1. Fossil record 2. Comparative anatomical structures 3. Comparative Embryology – comparing the embryos of species (ontogeny reflects phylogeny) 4. Genetic or molecular evidence – comparing the DNA of species Comparative Structures Homologous structures are “body parts” that are common in different species because they share a common ancestor. Whale fin / human arm are examples. Analogous structures are “body parts” that serve the same function but are very different in structure. Insect wings, bat wings and bird wings. Comparative Structures Vestigial structures: Seemingly purposeless structures like the appendix or tail-bone of humans. The number of identified vestigial structures have declined over the last several years because there purpose has been found. Speciation A process development that creates more than one species from a common ancestor. Only one known widely accepted example. The crocodile and the bird, both: 1. 2. 3. 4. build nests imprinting exhibited by young sound the same when first born scale tissue same as tissue that develops feathers Mechanisms of Speciation Divergent evolution – isolated populations evolve independently of one another. Typically some geographic barrier arises separating or dividing a population. Adaptive radiation – a founding species moves to an area with no competition, ie., the original founding finch in the Galapagos Islands, and adapts to the various niches within that ecosystem. Evolution is the theory that variation with natural selection optimally adapts an population to an environment. Environments can change though. Sometimes too quickly for evolution.