In this picture of Hegel, he looks unattractive by our standards. Was his plain hairstyle a nod to the revolutionary spirit? Or had wigs simply gone out of style between the 1770s and the time that this portrait was painted?
There's more that can be said, but the use of wigs dropped off dramatically in the 1790s, along with hair powder, as part of the "simplifying" changes I discussed in this previous answer, and by 1831 it was not at all radical for a man to not wear a wig.
