The recent news that Tiffany has featured a same-sex couple in its advertising for the first time demonstrates an important truth about the industry. Creatively, ads hold a mirror up to the society around them. Sometimes, of course, that mirror is distorted – a little like the ones found in those travelling fairs of yore. Instead of looking freak-show fat, we actually lose weight in the advertising mirror. Maybe some of our other imperfections are ironed out too. But unmistakably, we’re seeing some kind of representation of ourselves.

The mirror effect means that advertising is a particularly good way of charting social history. It tends to be largely agnostic about the big issues of the day while they’re still being debated, because it doesn’t want to come down on the wrong side.

Advertisers feel their job is to reflect the zeitgeist. Radicalism and the taking of clear positions is often perceived as too risky a strategy in a business built around persuasion. It’s better to play safe and reflect the status quo.  Ads therefore end up telling us a lot about society as it really is at a particular moment in time. When the status quo changes, the advertising changes alongside it – keeping pace with the society around it but rarely overtaking it.

The Tiffany ad is just one of the latest examples of this phenomenon. It shows how attitudes around same-sex relationships have changed dramatically over the past couple of decades. The company is not, in my view, making any more of a statement than saying ‘this is the new normal’.

Researching the history of Indian advertising for a forthcoming lecture, I have been struck by the clear divide between the colonial era and the years that followed. In the days of the Raj, advertising was often overtly aimed at a European audience and portrayed Indians in subservient roles. As independence grew nearer, it’s possible to find more evidence of the indigenous population being represented in ads. By the 1940s, for instance, Leela Chitnis – a famous actress associated with the Bombay Talkies studio – was endorsing Lux Toilet Soap. It was a small, but significant, step towards a more confident, independent advertising that was inspired by home-grown culture rather than influenced from London.

The same pattern appears to be in evidence all over the world. But could there be a case for saying that advertisers sometimes lead rather than follow?

Talking to a group from Maryland’s Towson University recently, we got on to the subject of the Coca-Cola ad which played at the Super Bowl a year ago.  The patriotic theme of America The Beautiful was rendered in a variety of different languages, reflecting the ethnic diversity of the USA.  A student asked me what I thought of the commercial and my response was that it was entirely in keeping with the brand values Coke has tried to champion over the years. The feelgood factor in the ad reminded me of the classic 1971 I’d like to buy the world a Coke spot.

Opinions had been, however, strongly polarised on social media about the 2014 ad. At one level, this might suggest that Coca-Cola was ahead of the curve – moving faster than was comfortable for the public in the States. I’d argue, however, that the USA is never going to demonstrate unanimity on what it means to be American. The culture of San Francisco or New York City is hugely different from Houston or Mobile.

Yes, Coke’s universal appeal means that it has to reach out to consumers in all those cities. But it’s never going to find an expression of American values that sits happily with everybody. So in taking a position here, it is reflecting one strong current of sentiment that already exists in the more liberal parts of the culture. It is pointing its mirror in a particular direction and framing one perfectly legitimate image of the US.  Other brands may tilt their own mirror in a different direction.

Jack Daniel’s or John Deere or Nike or Abercrombie & Fitch all give their own insights into the nature of American life. And it’s only when you see the patchwork quilt they create together that you get a sense for the true richness and diversity of the culture.