Modern Synthesis (2): The Contributions of Wright

In contrast to Fisher’sFisher, Ronald Aylmer genicgenic view of natural selection view of natural selectionselectionnatural, Wright’sWright, Sewall approach focused on gene combinations. One of Wright’sWright, Sewall most useful inventions was the method of path coefficients. Using the latter, he defined the inbreeding coefficient in 1922. Wright’sWright, Sewall biggest achievement was his shifting balance theory (SBTSBT) of evolution (1930, 1931), which was most efficient when a large population was divided into isolated (or almost isolated) groups. The SBTSBT is a three-phase theory: (i) genetic driftgenetic drift creates various gene combinations within groups, (ii) intragroupselectionintragroup selection creates local groups with high fitness, (iii) intergroupselectionintergroup selection results in the local groups with highest fitness making the most offspring contribution, followed by gene flowgene flow from the fittest to the less fit groups, thus increasing the overall fitness of the population. In a subsequent paper, WrightWright, Sewall used a visual metaphor called the adaptive landscapeadaptive landscape to illustrate his SBTSBT.