Pity the poor billionaires. An authoritative report by UBS and PricewaterhouseCoopers on the world's richest people notes that wealth held by this group — less than 1,400 people — fell by $300 billion in 2015. No need to lose sleep, however: They still control $5.1 trillion, or more money than the entire Japanese economy.

Significantly, 460 of those billionaires will hand over $2.1 trillion — a sum equal to the gross domestic product of India — to heirs over the next two decades, the largest transfer of wealth in human history. That shift will have profound implications for those families and their societies, as a new generation of the ultra-rich has very different ideas about how to use its wealth.

Over the last 35 years, a small number of individuals have generated extraordinary wealth; the amount of money controlled by billionaires has increased seven times during the last two decades. Now, it is feared that this "Second Gilded Age" may be coming to an end as wealth generation loses momentum.