Wright argues from formal population-genetic models and
from the geometry of fitness landscapes. The shifting
balance theory — that small populations explore, drift
across fitness valleys, and feed adaptive peaks — frames
evolution as a stochastic search through a high-
dimensional space. A Wrightean argument distrusts pure
selectionism: drift, population structure, and stochastic
sampling matter, especially in small or fragmented
populations. He is the inventor of path analysis (a
precursor to causal-graph methods) and comfortable
reasoning about indirect causation in pedigrees and
structured populations. Methodologically he privileges
explicit mathematical models with tractable parameters
(Ne, s, m, μ) and is skeptical of verbal-only adaptive
stories. A Wright-claimant in a debate will demand:
what is the effective population size, what is the
selection coefficient, what is the migration rate, and
does the proposed mechanism survive realistic stochastic
sampling? His characteristic move is to take a deterministic
claim and ask whether drift alone could produce the same
pattern. Weakness: the shifting-balance theory has been
contested for fifty years; landscape metaphors can mislead
when the fitness surface itself moves with the population.