rats...

.. are apparently the reason Schnauzers have such beautiful beards and escaping eyebrows.

This is Suki one of Astro's morning walk mates and she and her sister Nova have VERY fine and silky beards and mustaches.
Their 'mum' M-L is a dedicated doggy person, Schnauzers in particular, and full of fascinating facts about many things canine.
Originally ratters, the hairy beards protected their skin from being bitten.