(CNN) -- Books featuring Native Americans, on-the-run alien lovers, gay penguins and middle school theater geeks top the American Library Association's 2014 list of most challenged books.

The list, released Monday as part of the association's "State of America's Libraries" report, finds that a disproportionate share of the books feature non-white, gay or otherwise diverse characters.

The organization cited analysis by author Malinda Lo showing that 52% of books challenged in the past decade could be classified as "diverse."

"It's clear to me that books that fall outside the white, straight, abled mainstream are challenged more often than books that do not destabilize the status quo," Lo wrote on her website. "This isn't surprising, but the extent to which diverse books are represented on these lists -- as a majority -- is quite disheartening."

In all, the association said, it received notice of 311 formal written complaints in 2014 questioning the availability of books for myriad reasons: sex, drug use, homosexual themes, politics and offensive language, mostly.

The list is topped by "The Absolutely True Diary of a Part-Time Indian" by Sherman Alexie, which tells the story of a Native American youth born with disabilities attending a predominantly white high school.

The American Library Association said the book, which has appeared on the list for four years running, is frequently challenged as being anti-family, culturally insensitive and sexually explicit, among other things.

Alexie tweeted Monday that he is the "proud author of the most banned/challenged book of 2014!"

A sex-education book that includes cartoon depictions of naked bodies and sexual acts, "It's Perfectly Normal," also makes a repeat appearance on the list, as does "And Tango Makes Three," an illustrated book about two gay penguins raising a baby.

The serial "Saga" was one of three graphic novels included in the 2014 list, the others being "Persepolis" and "Drama."

"Persepolis" is an autobiographical tale of life in Iran during the Islamic revolution. "Drama" depicts middle school from the vantage point of the student leader of the school theater's tech crew.

"Saga" was frequently described as being "anti-family," the American Library Association reported, a stance that amused some fans. The book "depicts two lovers from long-warring extraterrestrial races ... fleeing authorities from both sides of a galactic war as they struggle to care for their newborn daughter," according to its publisher, Image Comics.

Charles Brownstein, executive director of the Comic Book Legal Defense Fund, told the Washington Post on Monday that the presence of three graphic novels on the list shows that "comics are clearly a vital aspect of the current culture," shining a spotlight all the things dividing us.

"The books on this list address issues of race, sexuality, sexual preference, religion, substance abuse and many other concerns related to contemporary life," he told the Post. "That's the job we charge our authors with: using art to provide a safe place for audiences to engage with topics of substance in a way that allows them to make their own conclusions."

"Unfortunately, many (people) would prefer to remove those discussions altogether rather than trust that each individual is capable of making the best decisions possible for themselves or their children," the newspaper quoted him as saying.

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