In a perfect world, a man's name MacBean should track perfectly with his Y-chromosomal DNA, as both are passed down unchanging from father to son.

There are several ways to disrupt the continuity: issues of paternity, genetic mutation (v. slow on the Y chromosome), the fact that last names are relatively recent, and that families change their names.

I suspect it is the only way to bridge gaps in knowledge for some folks. Don't expect definite answers: science, and especially biology, are always a bit statistical.