POSTULATES FOR EVOLUTION VIA NATURAL SELECTION 1. Phenotypic variation is present among individuals...

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 TOANOTHER

FITNESS (W) – ABILITY OF AN ORGANISM TO SURVIVE/REPRODUCEIN ITS ENVIRONMENT

ABSOLUTE W = NUMBER OF OFFSPRING PRODUCED BY AN INDIVIDUALWITHIN 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 = 1wb = 9/18 = 0.5 “ w = 0.5/1.5 = 0.33

Examples of microevolution involving humans

1. Lactose Tolerance

2. Skin color

4. CASE STUDY: HIV and human co-evolution

3. Fisheries

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 phenotypicvariation within HIV that affects virulence;consider the host and its response to selection

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