Figure 2. Mean unfolding stability 
versus misfolding stability 
for neutrality exponent 
(non-neutral regime).
The sets of points joined with solid lines correspond to constant GC usage, between 
(largest 
) and 
(largest 
). 
grows and 
decreases with 
. The sets of points joined with dashed lines correspond to constant population size 
, from 
(smallest stability) to 
(largest stability). Both stability variables 
increase with 
. Data points are superimposed to a heat map of the fitness function, showing that fitness increases with 
. However, constant 
lines do not correspond to constant fitness, but there are small variations, from which the optimal GC usage is derived. The solid white line shows 
at which the selective pressures on 
and 
balance. One can see that, at large 
, 
is smaller than 
for all 
, so that the selective pressure is stronger on the former.