For decades, one of the core ways we refined a specific advertising audience was through segmentation, including gender. We would then craft our marketing messages based on that segmentation and our assumptions about that audience.

It’s why minivans are almost always marketed to women and men get targeted for the sports cars. Can you think of a laundry detergent commercial that spoke to men? I can’t – but if there was one, I can almost promise it would be about him being too dumb to do the laundry, messing it up and his wife and detergent X coming to the rescue.

Even worse than mocking the genders for what they stereotypically aren’t good at is when the advertisers try too hard to prove they aren’t gender biased.

This practice isn’t solely based on our own perceptions and opinions about men and women. We’ve seen plenty of research to explain and defend this practice of gender typing for messaging purposes. The research has shown that women’s and men’s brains are wired differently. Women remember product details, and men like to understand how something works. Women respond to sounds and smells, and men are visually stimulated.

When this focus on gender messaging trickles down to marketing to children, it gets even more interesting. If a retailer puts the Barbies, Easy-Bake Ovens and dress-up clothes under a sign that says GIRLS or against a pink wall, it could be argued that we are not only stereotyping but we’re sending the message to girls that they shouldn’t play with the baseballs and light sabers (which of course are against a blue wall or have a BOYS sign hung overhead).

In fact, we’re supplying the very toys that teach the characteristics we think are already inherent in the gender. Girls get toys that teach nurturing and caregiving, while boys are given toys that lend themselves to competition and conflict.

This has been the status quo for as long as advertising has existed. Though we may bristle at it occasionally, for the most part, it’s the norm, and we accept it. But there’s a school of thought that says it may be slowly on its way out.

A marketplace truth that’s bringing about the shift is that the millennials don’t look at gender the same way their older counterparts do. Both genders are much more comfortable with the idea that the genders are truly equal and can partner in new ways. Some very gender-specific products like fragrances are paying attention. Dolce & Gabbana recently launched a fragrance line defined by personality, not gender. Buyers choose a fragrance based on how they see themselves, such as the dreamer or the charmer or even the seducer.

But to remind us that this is complicated stuff, a recent study showed that both millennial men and women would like to bring back more chivalry. So the new definition of gender is still being formed.

Another place we see the shift is social media. One aspect of social networks that doesn’t get much attention is the idea that social media, by its very nature, groups people according to their interests, not their demographics. People tend to flock together based on their passions, hobbies, careers or talents. This might force advertisers to re-think how they define their target audiences.

Drew McLellan is Top Dog at McLellan Marketing Group and blogs at www.drewsmarketingminute.com. He can be reached by email at Drew@MclellanMarketing.com. © 2011 Drew McLellan