  While Neutral Theory famously describes the number of discrete genetic
differences in populations, we consider the number of genetic backgrounds under
which such differences are observed - setting limits to the generalizability of
their effects. This allow us to determine which population structures and
diversity rates have maximal effect generalization across (1) environmental and
(2) genetic variation, and to demonstrate that they correspond asymptotically
to those of populations under (1) natural selection and (2) drift. At the same
time, these results suggest distinct limits to the predictability of fitness
and evolution across evolutionary regimes. We employ both broad time,
large-scale genome sequencing datasets (including whole-genome autocorrelation
calculations), and fine time-scale barcoding experiments.
