  Due to stochastic fluctuations arising from finite population size, known as
genetic drift, the ability of a population to explore a rugged fitness
landscape depends on its size. In the weak mutation regime, while the mean
steady-state fitness increases with population size, we find that the height of
the first fitness peak encountered when starting from a random genotype
displays various behaviors versus population size, even among small and simple
rugged landscapes. We show that the accessibility of the different fitness
peaks is key to determining whether this height overall increases or decreases
with population size. Furthermore, there is often a finite population size that
maximizes the height of the first fitness peak encountered when starting from a
random genotype. This holds across various classes of model rugged landscapes
with sparse peaks, and in some experimental and experimentally-inspired ones.
Thus, early adaptation in rugged fitness landscapes can be more efficient and
predictable for relatively small population sizes than in the large-size limit.
