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POSTULATES FOR EVOLUTION VIA NATURAL SELECTION

POSTULATES FOR EVOLUTION VIA NATURAL SELECTION. 1 . Phenotypic variation is present among individuals in the population. 2. At least some of this phenotypic variation is due to underlying genetic variation; i.e., it is heritable.

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POSTULATES FOR EVOLUTION VIA NATURAL SELECTION

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  1. POSTULATES FOR EVOLUTION VIA NATURAL SELECTION 1. Phenotypic variation is present among individuals in the population 2. At least some of this phenotypic variation is due to underlying genetic variation; i.e., it is heritable 3. Reproduction is non-random; it is related to the phenotype of the individual (reproductive output varies among phenotypes) 4. Not all individuals that are born/hatched etc can survive or reproduce at the same rate; environments have carrying capacities (K)  if true, then evolution via NS MUST occur DIFFERENTIAL/SURVIVAL OF ONE PHENOTYPIC VARIANT RELATIVE TO ANOTHER

  2. FITNESS (W) – ABILITY OF AN ORGANISM TO SURVIVE/REPRODUCE IN ITS ENVIRONMENT ABSOLUTE W = NUMBER OF OFFSPRING PRODUCED BY AN INDIVIDUAL WITHIN A POPULATION RELATIVE W = NO. OFFSPRING PRODUCED BY AN INDIVIDUAL RELATIVE TO THE MEAN NO. OFFSPRING PRODUCED BY ALL INDIVIDUALS OF THE POPULATION [usually standardized to 1] Example: phenotype (variant) a = 27 offspring phenotype b = 9 offspring mean of population = 18 offspring wa =27/18 = 1.5  standardized w = 1.5/1.5 = 1 wb= 9/18 = 0.5  “ w = 0.5/1.5 = 0.33

  3. Examples of microevolution involving humans • Lactose Tolerance • Skin color 3. Fisheries 4. CASE STUDY: HIV and human co-evolution

  4. Future of AIDS Epidemic? • will HIV-1 ‘automatically’ become less virulent so as not to kills hosts? • what can we do to reduce the virulence of HIV? (i.e., can we change the ‘biology’ Of HIV)? Selection Thinking Needed: consider HIV and possible phenotypic variation within HIV that affects virulence; consider the host and its response to selection

  5. 1). Selection should act on virus to maximize its fitness • Fitness of faster reproducing variant relative to slower reproducing variant should depend on the probability and frequency of transfer to new hosts (why?) 2). Rapid and frequent transfer favors: Slower inter-host transfer favors: Human Evolutionary Response

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