  We study the relative importance of "top-speed" (long-term growth rate) and
"acceleration" (how quickly the long-term growth rate can be reached) in the
evolutionary race to increase population size. We observe that fitness alone
does not capture growth rate: robustness, a property of neutral network shape,
combines with fitness to include the effect of deleterious mutations, giving
growth rate. Similarly, we show that growth rate alone does not capture
population size: regularity, a different property of neutral network shape,
combines with growth rate to include the effect of higher depletion rates early
on, giving size. Whereas robustness is a function of the principal eigenvalue
of the neutral network adjacency matrix, regularity is a function of the
principal eigenvector. We show that robustness is not correlated with
regularity, and observe in silico the selection for regularity by evolving RNA
ribozymes. Despite having smaller growth rates, the more regular ribozymes have
the biggest populations.
