Rich offspring helped drive the growth, with people who inherited at least part of their fortunes representing the fastest growing segment among billionaires, with growth of nearly 30% year over year.
"Wealth helps accumulate more wealth," David Barks of Wealth X said to the Wall Street Journal, explaining how the small group continues to get richer each year, regardless of market conditions.
Billionaires who are under 35
Billionaires who are under 35
Billionaires who are under 35
CEO Mark Zuckerberg gestures while delivering the keynote address at the Facebook F8 Developer Conference Wednesday, March 25, 2015, in San Francisco. (AP Photo/Eric Risberg)
FILE-In this Thursday April 26, 2012, file photo, Dustin Moskovitz co-founder of the collaborative software company Asana, poses outside of his office in San Francisco. Facebook co-founder Dustin Moskovitz has been selling 150,000 shares of Facebook stock a day out of the hundreds of millions that he owns. So far, he has shed 1.35 million shares for proceeds of $26.2 million, at prices ranging from $18.79 to $20.08. (AP Photo/Eric Risberg)
Billionaire Elizabeth Holmes, founder and chief executive officer of Theranos Inc., speaks to the media as she arrives at a state dinner hosted by U.S. President Barack Obama and U.S. First Lady Michelle Obama in honor of Japan's Prime Minister Shinzo Abe at the White House in Washington, D.C., U.S., on Tuesday, April 28, 2015. Prime Minister Shinzo Abe goes before the U.S. Congress on Wednesday to present Japan as a stalwart ally that's willing to play a bigger military role in Asia, a message likely to be embraced in Washington and greeted with suspicion in Seoul and Beijing. Photographer: Andrew Harrer/Bloomberg via Getty Images
Nathan Blecharczyk, co-founder and chief technology officer of Airbnb Inc., speaks during the 2015 Bloomberg Technology Conference in San Francisco, California, U.S., on Monday, June 15, 2015. The conference gathers global business leaders, tech influencers, top investors and entrepreneurs to shine a spotlight on how coders and coding are transforming business and fueling disruption across all industries. Photographer: David Paul Morris/Bloomberg via Getty Images
Brian Chesky, chief executive officer of Airbnb Inc., speaks during an interview at a media event in Johannesburg, South Africa, on Monday, July 27, 2015. Airbnb is hoping to spread its unique brand of hospitality throughout Africa. Photographer: Waldo Swiegers/Bloomberg via Getty Images
Airbnb online accommodation provider co-founder and Chief Product Officer, Joe Gebbia announces to the media their partnership with the Brazilian Olympic Committee for the Rio 2016 Olympic Games at the headquarters of the Brazilian Olympic Committee in Rio de Janeiro, Brazil, on March 27, 2015. AFP PHOTO / YASUYOSHI CHIBA (Photo credit should read YASUYOSHI CHIBA/AFP/Getty Images)
PARIS, FRANCE - JANUARY 26: Tatiana Casiraghi attends the Christian Dior show as part of Paris Fashion Week Haute Couture Spring/Summer 2015 on January 26, 2015 in Paris, France. (Photo by Pascal Le Segretain/Getty Images)
NEW YORK, NY - APRIL 22: Snapchat co-founder and CEO Evan Spiegel speaks during the iHeartMedia Soundfront at iHeartMedia Headquarters on April 22, 2015 in New York City. (Photo by Michael Loccisano/Getty Images for iHeartMedia)
Bobby Murphy, chief technology officer and co-founder of Snapchat Inc., speaks during a Google Inc. Cloud event in San Francisco, California, U.S., on Thursday, March 25, 2014. Google Inc. cut prices on some Internet-based services for businesses by 30 percent or more, stepping up a challenge to Amazon.com Inc. and Microsoft Corp. in cloud computing. Photographer: David Paul Morris/Bloomberg via Getty Images
Snapchat co-founders Evan Spiegel and Bobby Murphy attends the Time 100 Gala celebrating the Time 100 issue of the Most Influential People In The World at Jazz at Lincoln Center on April 29, 2014 in New York. AFP PHOTO / Timothy A. CLARY (Photo credit should read TIMOTHY A. CLARY/AFP/Getty Images)
Adrian Cheng, executive director of Chow Tai Fook Jewellery Group Ltd., attends the companys annual results news conference in Hong Kong, China, on Tuesday, June 18, 2013. Chow Tai Fook, the worlds largest listed jewelry chain, reported a 13 percent decline in profit on higher costs and weaker consumer spending. Photographer: Jerome Favre/Bloomberg via Getty Images
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To be fair, it remains true that most billionaires are not heirs or heiresses. More than half — 56% — of billionaires are self-made, according to the Wealth X census.
But there are also a number of alarming trends in the data for those concerned about income inequality, especially with regards to gender: The wealth gap between men and women, for instance, persists even among the world's wealthiest people — and is growing.
The disparity between male and female billionaires grew between 2014 and 2015, from 8.1 men for every one woman, to 8.4 in the latest data. The percentage of billionaire wealth held by men also climbed, from 87.2% to 88.6%.
Income inequality more broadly has been a hot-button issue in the 2016 presidential campaign for both parties.
Most Americans did see wage growth in the last year, with the bottom 99% of incomes growing 3.9%, but incomes for the top 1% of earners still grew far faster, at 7.7%.
Generally, income inequality in the United States has been on the rise for decades: In 2013, the amount of wealth held by the richest 1% of Americans reached the same level it was in 1928, when the richest 1% of Americans captured almost 24% of total income.
There's now solid evidence that current generations of Americans will actually be poorer than their parents: Between 30% and 40% of American workers may never see a pay raise again, according to a study published in July by the McKinsey Global Institute.
Alas, the disparity in earnings between the rich and poor (or middle class) is not without societal consequences.
We are also already seeing other effects of income inequality on social institutions like marriage. People in areas of high income inequality, for example, are more likely than those in areas of greater equality to have children before getting married, according to a recent study from Johns Hopkins University.