What does the quote ads are the cave art of the 20th century mean by marshall mcluhan?

Marshall McLuhan's quote "ads are the cave art of the 20th century" suggests that advertisements serve as a primary form of cultural expression and communication in modern society, akin to how cave art represented the thoughts and values of early humans. Just as cave art provided insight into the lives, beliefs, and environments of our ancestors, advertisements reflect the desires, aspirations, and social dynamics of contemporary culture. This comparison highlights the significance of advertising as an influential medium that shapes and mirrors societal trends and human behavior.