Regression to the mean and evolution
TL;DR answer: Regression to the mean doesn't always occur (children can be taller than either parent, as can be easily observed at any high-school basketball game), so it doesn't affect the theory of evolution through natural selection.

The observation of regression to the mean was of great concern to Darwin and early thoughts on natural selection (don't confuse "evolution", which is the observed phenomenon, and "natural selection", which is one of the theories proposed to explain evolution).  The problem has been effectively resolved since the rediscovery of Mendel's genetic work at the end of the 19th century.

"Regression to the mean" is inevitable if inheritance works through blending of features.  That was how everyone believed inheritance to work in the mid-1800s, and Darwin understood that it presented an insuperable obstacle to his theory.  That is, if blending inheritance was true, then natural selection could not be true.  Darwin puzzled over this quite a bit, and came up with some unsatisfying suggestions to overcome it, but at the end of the day, one of the predictions that his theory of evolution through natural selection made, was that blending inheritance could not be true.

Of course, blending inheritance is not true.  Mendel showed that in fact inheritance is quantal, not blending.  We now know that many traits of interest look, superficially, as if they're blending (which leads to regression to the mean), but are actually the result of multiple traits interacting.  

With blending inheritance, the variation that is required for natural selection to work is lost, generation after generation; regression to the mean in an inevitable consequence.  With gene-based inheritance, variation (can be) preserved generation after generation; regression to the mean is a common but not inevitable consequence, because the variation in the original population is still present and can be re-created given appropriate selection pressure.