Every few years or so, the members of the Academy of Motion Picture Arts and Sciences like to congratulate themselves on achieving a milestone that demonstrates their tolerance, open-mindedness, and progressive thinking.

When Halle Berry became the first African-American performer to take home the best actress prize in 2002, for instance.

Or when Kathryn Bigelow was given the best director trophy in a small but unprecedented step forward for women filmmakers.

These moments, however, tend to be few and far between, as evidenced by tomorrow’s Oscar ceremony, the second in a row to egregiously exclude black and minority nominees. Thus, the resurrection of last year’s popular Twitter hashtag, #OscarSoWhite.

The lack of diversity in the 88th Academy Awards is even more glaring when you consider the talent Academy voters overlooked this year.

A biopic of seminal rap group N.W.A., “Straight Outta Compton” was critically well received and a box office hit, yet managed to snag only one nomination — for best original screenplay — when many expected it to garner a best picture nod.

The “Rocky” spin-off “Creed” was also critically acclaimed but was shut out, save for a best supporting actor nomination for the film’s sole white star, Sylvester Stallone.

This despite the talents of director Ryan Coogler and star Michael B. Jordan, who previously failed to earn much deserved nominations for their work together in the devastating “Fruitvale Station.” Jordan’s leading lady, Tessa Thompson, also turned heads with her performance.

Other seeming shoo-ins who were not nominated include Idris Elba,for his villainous turn in “Beasts of No Nation,” Elba’s astonishing young co-star, Abraham Attah, and Benicio Del Toro, recognized by several other groups for his supporting turn in “Sicario.”

Chagrin over the Academy’s blatant lack of inclusion has resulted in threats of boycotts — at least on the part of Spike Lee and Jada Pinkett-Smith — and the following statement of remorse issued by (black) Academy president Cheryl Boone Isaacs:

“I am both heartbroken and frustrated by the lack of inclusion. This is a difficult but important conversation, and it’s time for big changes. The Academy is taking dramatic steps to alter the makeup of our membership.

“… As many of you know, we have implemented changes to diversify our membership in the last four years. But the change is not coming as fast as we would like.”

Indeed, Academy demographics remain alarmingly exclusive. According to the Los Angeles Times, voters are 91% white and 76% male.

The newspaper reported that in 2012, the voting population was 94% white and 77% male, a makeup very similar to what we see today.

Though the Academy has made an effort to recruit more women and minority — not to mention younger — voters to their ranks, progress is slow in an organization in which members are appointed for life.

All things considered, it’s easy to see why a film like “Straight Outta Compton,” which was just as crowd-pleasing, stylishly directed and thrilling as best picture nominees “Brooklyn” or “The Martian,” could be passed over.

An aging, white audience is probably more likely to relate to the tale of a young Irish immigrant adapting to life in 1950s (aka the good, old days) New York or a saga that glorifies NASA (although it must be said that “The Martian” cast is surprisingly diverse) than a group of rebellious hip-hop artists who regularly ran afoul of the law while rising to the status of rap legends.

Despite losing its momentum to a certain degree in its third act, it’s hard to deny that “Straight Outta Compton” is best picture material. The scene in which Ice Cube, Eazy-E and Dr. Dre defy a police order to perform their infamous anti-cop anthem in a packed Detroit concert hall is as electric a cinematic moment as ever there was.

But let’s face it, if Cube and company were to take the stage to claim Oscar’s top prize, it would be as surreal a moment as when, in 2006, Three 6 Mafia won for their ditty “It’s Hard Out Here for a Pimp” from “Hustle & Flow.”

(This remains, hands down, one of the most amazing Oscar moments of all time.)

The Academy claims it wants to change.

Last month, the organization resolved by 2020 to double the number of women and minorities included in its voting body and instituted new rules allowing the revoking of voting privileges from inactive members.

These measures are a show of good faith, but the fact remains that the Academy isn’t going to change its ways until Hollywood does.

According to the L.A. Times, the group’s demographics reflect the realities of an industry that weaves a cocoon of opportunity, wealth and privilege around a tight band of almost exclusively white insiders.

“The executive branch (of the Academy), which finances the movies and determines what films warrant an awards campaign, is 98% white,” the newspaper said.

“The public relations branch, which strategizes those awards campaigns, is 95% white.

“Other branches reflect the entrenched nature of certain hiring patterns in Hollywood crafts, such as visual effects, which is 98% male, and cinematography, which is 95% male.”

Meanwhile, a recent study reports that only 29% of Hollywood speaking roles are filled by women.

It’s certain that tomorrow night’s Oscar host, Chris Rock, will have a few things to say on this subject.

The comedian recently detailed the absurdities of Hollywood’s racial bias in a blunt, funny, evenhanded essay about the city he works in.

“It’s a white industry,” Rock writes.

“Just as the NBA is a black industry. I’m not even saying it’s a bad thing. It just is.”

Rock points out that, if you happen to be in the minority, Hollywood is a tough place to break into even at the most basic, unskilled job levels.

He writes that there is no such thing as color blind casting in Hollywood (“It was never like, ‘Is it going to be Ryan Gosling or Chiwetel Ejiofor for ‘Fifty Shades of Grey.'”) and that black women may be the most neglected of all performers in the film industry (“You can go to whole movies and not see one black woman.”)

Rock ends his essay on a hopeful note, saying that “change just takes time.”

Let’s hope it doesn’t take 20 more years of #OscarSoWhite for one of America’s greatest industries to correct a wrong it can no longer pass off as just one group’s problem.

Photos: http://www.bet.com, http://www.youtube.com, oscars.go.com.