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Name _________________________________________________ Date _____________________ Period _________ Natural Selection (Darwin’s Mechanism) Natural Selection – the process by which organisms that are better suited to an environment survive and reproduce in greater number than those less suited. What causes Natural Selection? _____________________________________ Steps of Natural Selection 1. Overproduction—All species over reproduce creating a population with many __________ (alleles) – the total of all _________ (or variations) in the population is called a _______________ 2. Inherited Variation—______________ within a population come from _______________ & __________ ____________ changing the population’s gene pool. 3. Struggle to Survive—Organisms ___________ for resources such as food, shelter, and mates. Those _____________________ to meeting these needs will ____________. Not all members of the species will survive this competition. Only some will survive and have the opportunity ______________________ their ______________________. 4. Successful Reproduction—Successful _____________ are passed to the next ________________. Now, more members of the population are being born with the ______________ variation than those with the __________________ trait. 5. Adaptation of the Species—process by which a species becomes better __________ to its environment. Examples of Natural Selection 1. 2. 3. Discussion Questions: 1. According to Natural Selection, explain why human over population exists? 2. Is the human species still evolving? Explain. Name _________________________________________________ Date _____________________ Period _________ Speciation (Steps to a New Species) Speciation – The formation of a new species by the change of allele frequency (traits) due to natural selection. Species – a group of organisms that can interbreed and produce fertile offspring. Steps of Speciation 1. Separation / Isolation: What could cause separation? 2. Adaptation: Natural selection improves the fit between ____________ & ____________________ created from ___________ in the gene pool. 3. Divergence: _________________ in the gene pool _______________ between populations. Eventually this could lead to a _____________________. Examples of Speciation 1. 2. 3. Factors Contributing to Speciation 1. Isolating Mechanisms - Genetic differences __________ ____________ among related species, helping to cause speciation. This can happen before or after mating. 2. Genetic Drift - A loss of ____________ ____________ (alleles) brought about by ___________. Usually in small populations. 3. Founders Effect - A loss of genetic variation from a ________ ____________established and genetically _____________ from a larger population (usually contains some rare variations (alleles) making the gene pool different from the original). Example: 4. Migration - Gene pools of smaller populations change from the ____________ & ___________ of individuals from _____________ populations with unique variations (alleles) Pace of Evolution (1) Gradualism - (2) Punctuated Equilibrium -