Over the past 50 years, the U.S. population has become increasingly diverse: According to the most recent census, 36% of the American population now identifies as non-Caucasian–that's in comparison to just 16% in 1970. The idea of what it means to be American and to look American this July 4, 2013, is vastly different than the July 4ths of half a century ago. So how has this changed the American beauty ideals, and, by default, the American modeling industry?

Unfortunately, the modeling industry has been slow to catch on to America's shifting demographics. Runways and ad campaign are still overwhelmingly white. However, there has been some progress. Recently there's been an influx of models of color; many of them, like Joan Smalls, Chanel Iman, and Soo Joo Park, are from the U.S.–and they're helping redefine what that "All-American" look means today.

For decades, the term "All American" meant blond-hair, blue eyes and Nordic features. Casting Director Julia Samersova calls it the "All American Blonde Goddess" archetype. Time magazine, in a March 1978 cover story called "The All-American Model," described it as the "California look." Models who had it were tanned, blonde, blue-eyed, "healthy," and "strong." Cheryl Tiegs was on the cover.

But a lot has changed since then. In a 2011 study of 2,000 Americans (male and female), Allure found that 85 percent "believe that increased diversity in this country has changed what people consider beautiful." 64 percent of said they "think women of mixed race represent the epitome of beauty." Angelina Jolie was found to be the celebrity that most personified "American beauty ideals." In Allure's 1991 study on the same subject, that honor went to blond-haired-blue-eyed Christie Brinkley.

Today's top American models (as ranked on Models.com) are Joan Smalls, Arizona Muse and Karlie Kloss. Yet, as different as those models may look from Tiegs, or Tiegs' forebearer, Lauren Hutton, they do share some commonalities (besides, you know, citizenship).

Physical health and robustness along with a fresh-faced wholesomeness–qualities Kloss, Muse, Smalls along with Tiegs and Hutton, have in spades–are cornerstones of the quintessential American look. "Sexy, in a clean way," Samersova said. "All-American" redirects to "Girl Next Door" on Wikipedia. Most important is the impression of approachability, warmth, and openness.

"[Smalls, Muse and Kloss] have that intoxicating mix of being totally and ridiculously gorgeous, and yet accessible and somehow attainable at the same time," Samersova said. "Women want to be them and men want to bang them."

That's remarkably similar to Time's description of Tiegs: "[T]he one overriding reason for Tiegs' appeal is that her sexiness is not forbidding to men or offensive to women."

That, more than race or hair color, defines the "All-American" model today. "The All American look today is what America looks like in general," Samersova said. "We are the melting pot of the world! Black, Hispanic, Native American, Asian, and Caucasian. That is the beauty of the All American look–We can BLEND all these gorgeous races together! It can literally be anything! We've come a long way baby! Global beauty is where it's at!"

Take a look at how the "All-American" model has evolved from the '60s to today.

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