Lecture 11: Shifting Balance

Question 1

What are the three phases of Wright’s “shifting balance”?

Answer 1

1. Drift in local populations
   - approach domain of attraction of local peak
2. Mass selection (Intrademic selection)
   - climb local peak
3. Interdemic selection
   - emigrants proportional to relative fitness among demes; all demes acquire allele frequencies of ‘best’ global peak

Question 2

How does evolution and genetic drift work to reach highest peak?

Answer 2

Evolution is short sighted, may trap population at local peak. Genetic drift may enable a population to acquire new allele frequencies and combinations that enable selection towards the highest peak.

Question 3

What is the Fisher-Wright Debate?

Answer 3

Fisher - Mass selection is the dominant force in evolution. Wild type alleles evolve to become dominant.

Wright - Drift interacts with selection to reach high fitness. Selection to increase dominance must be very weak.