> Evolution works on a breeding population, typically consisting of a large number of individuals.

Right. However, the direction evolution takes is not preordained. Many factors are at work, including "stabilizing selection" which keeps a population from evolving away from a "happy medium" and reduces the likelihood of radical change. Also, "neutral changes" can eventually differentiate populations. 

Stabilizing selection is known to be the most
prevalent type of natural selection; it favors the
intermediate (average) phenotype of the trait, and
in doing so it removes the extreme phenotypes of
the trait from the population. 

Thus, stabilizing selection reduces genetic variability in 
the population. It is generally accepted that stabilizing
selection maintains the DNA and protein sequences over
evolutionary time. However, Kimura demonstrated
that under stabilizing selection, extensive neutral
evolution can occur through random genetic drift. 

In other words, many cryptic neutral genetic changes
may occur in natural populations while maintaining
the phenotype unchanged.

Supratim Choudhuri (2014) BIOINFORMATICS

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