Figure 5: Comparison of Roulette and CHC selection
When using traditional roulette wheel selection, the best
individual has the highest probability of survival but does not
necessarily survive. We use CHC selection to guarantee that the best
individual will always survive in the next generation. In CHC selection
if the population size is N, we generate N children by using
roulette wheel selection, then combine the N parents with the
N children, sort these 2N individuals according to their
fitness value and choose the best N individuals to propagate to the next
generation.
From Figure 5, we can see that with CHC selection the
population converges quickly compared to roulette wheel selection and
the performance is also better.
But fast convergence means less exploration. To prevent convergence
to a local optimum, when the population has converged we save the
best 
of the individuals and re-initialize the rest of the population
randomly. We call this modified CHC selection R-CHC. From
Figure 6, we can see that at first, the performance of
CHC and R-CHC are almost the same, but during
later generations the performance with R-CHC is better
than the performance with CHC only.
Figure 6: Comparison of CHC selection with or without re-initialization