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Lecture 4

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BIOL 359
Jonathan Witt

Lecture 4: Intro Natural Selection  Natural Selection: o Developed by Darwin ; explains how evolution can occur o The book: the origins of species by means of natural selection is devoted to explaining this mechanism o Natural Selection: differences in survival and reproduction of phenotypes leading to differences in their contribution the next generation, resulting in a change in frequency of heritable phenotypic variations in populations overtime  Components of Natural Selection: o Living things produce more offspring than can be supported o There is a constant struggle for existence. o Individuals in a population vary in their phenotypes. o Some of this variation is heritable (genotypes). o Those individuals best adapted to current conditions are most likely to survive and reproduce themselves o If these adaptations are heritable, they will be passed on to their offspring.  NOTE: o Natural selection acts on phenotypes, but only if there is a change in allele frequencies (eg Gene Frequencies) in a population has evolution occurred. o Population genetics is the study of allele and genotype frequencies and their changes in entire populations.  Evolutionary Fitness ( Darwinian Fitness) o The term ‘fitness’ refers to an individuals contribution to the next generation in terms of number of offspring o The more offspring an individual contributes to the next generation, the greater the individuals evolutionary fitness  Measure of Fitness: o Fitness is a measure of reproductive success, which is a
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