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Transcript
NATURAL SELECTION The unequal survival and reproduction of organisms due to environmental forces, resulting in the preservation of favorable adaptations. The Two Steps of Natural Selection are: 1. The production of variation in a population 2. Limited aspects of survival and reproduction DARWIN’S NATURAL SELECTION: 3 REQUIREMENTS 1. There is variation in traits in the population: For example; some beetles are green & some are brown. 2. There is limited reproduction: - Not all individuals get to reproduce to their full potential. 3. Traits are able to be inherited - Traits have a genetic basis. The more advantageous traits allow more offspring. If you have variation, limited reproduction, and heredity, you will have evolution by natural selection. THE 4 MAIN PRINCIPLES OF NATURAL SELECTION ARE: 1. Variation: Differences in physical traits of an individual from the group to which they belong. 2. Overproduction: Raises the chances of survival and results in competition for resources. 3. Adaptation: Inherited trait that is selected for over time because it allows organisms to better survive in their environment. 4. Descent modification: Overtime natural selection will result in species with adaptations that are well suited for survival and reproduction in an environment. NATURAL SELECTION Step One: The Production of Variation. (Chance) •Mutations •Meiosis:recombination due to crossing-over •Random mate selection & fertilization What different wild species do we see variation in? Step Two: Limited aspects of survival and reproduction •Superior success of certain phenotypes •Non-random mate choice ARTIFICIAL SELECTION Nature provides variation, humans select variations that are useful. Ex: a farmer breeds only his best livestock. ARTIFICIAL SELECTION Agriculture Corn looks very different from its ancestor 6 NOBODY!! There is no agent involved in natural selection. Natural selection is a process of elimination. INDIVIDUALS THAT HAVE TRAITS THAT ARE BEST ADAPTED FOR THE CURRENT ENVIRONMENT ARE THE ONES THAT SURVIVE TO BREED AND PASS ON THEIR GENES TO THE NEXT GENERATION. Organisms not possessing the beneficial traits either die or don’t have as many offspring or adapt to a new way of life. EVOLUTIONARY FITNESS Evolutionary Fitness: The probability that the line of descent from an individual with a specific trait will not die out If a gene is ‘fit’, then it is likely to benefit an organism in their environment. If the environment changes, then it may no longer be ‘fit’ ENVIRONMENTAL CHANGE When faced with a change in environmental condition, a population of a species can get MAD: MIGRATE to a more favorable location ALREADY be adapted DIE - Extinction MUTATIONS, MY FRIENDS! Changes in the structure of the DNA Adds genetic diversity to the population – Speciation. May or may not be adaptive Depends on the environment! MECHANISMS OF NATURAL SELECTION Gene Flow: the movement of genes into or out of a population. MECHANISMS OF NATURAL SELECTION SELECTION PRESSURE ON A POPULATION • Competition for food • Competition for a mate • Changes in the environment • Predators • Parasites