Why did Roman senators have their wrinkles and warts carved in marble?

Because in Republican Rome, a wrinkled face was a credential. Verism was a highly realistic style of Roman portrait art, used mainly for politicians, whose facial imperfections were rendered in detail or, according to some scholars, even exaggerated to highlight their maturity, experience and gravitas. It emerged in the late Roman Republic, between 147 and 30 BC. Age was highly valued and was synonymous with power, since one of the only ways to hold power in Roman society was to be part of the Senate.

There was a second reason, and it concerns beauty. The Greeks, whose portraits strived for idealization, believed that a good man must be beautiful. Roman portrait sculpture was far more natural and is still considered one of the most realistic examples of the genre in the history of art. Showing arguably ugly features was a way of showing confidence, placing a value on strength and leadership above superficial beauty. And it is widely held that in the ancient world physiognomy revealed character, so the features in a veristic bust could be taken to express virtues the Republic admired.

Scholars still disagree about how literal the portraits are. It is debated among scholars and art historians whether they were truly blunt records of actual features or exaggerated features designed to make a statement about a person's personality.

The fashion did not last: under Augustus and the Julio-Claudians, Greek Classical sculpture featuring "eternal youth" was favored over verism, and Augustus himself is always shown as a man of about 35, although some images were made when he was in his seventies.