Physicist Stephen Hawking warns that money and our attitude toward wealth was a key factor in the outcome of the EU Brexit referendum, but it also is a warning that "envy and isolationism" threaten the future of humanity.

The June 23 Brexit vote was down to British attitudes towards wealth and money and that it was time for an "honest" debate about "the role that wealth does and doesn't play in our society," Hawking wrote in the U.K. Guardian newspaper.

Hawking said he was "sad” about the Brexit result. “But if I've learned one lesson in my life it is to make the best of the hand you are dealt," he wrote. "Now we must learn to live outside the EU, but in order to manage that successfully we need to understand why British people made the choice that they did," he wrote. "I believe that wealth, the way we understand it and the way we share it, played a crucial role in their decision," he wrote.

"We are in perilous times. Our planet and the human race face multiple challenges. These challenges are global and serious – climate change, food production, overpopulation, the decimation of other species, epidemic disease, acidification of the oceans. Such pressing issues will require us to collaborate, all of us, with a shared vision and cooperative endeavor to ensure that humanity can survive," he wrote.

"We will need to adapt, rethink, refocus and change some of our fundamental assumptions about what we mean by wealth, by possessions, by mine and yours. Just like children, we will have to learn to share," he wrote.

He warned that "if we fail, then the forces that contributed to Brexit, the envy and isolationism not just in the U.K. but around the world that spring from not sharing, of cultures driven by a narrow definition of wealth and a failure to divide it more fairly, both within nations and across national borders, will strengthen," he wrote.

"If that were to happen, I would not be optimistic about the long-term outlook for our species," he added. "We can and will succeed. Humans are endlessly resourceful, optimistic and adaptable. We must broaden our definition of wealth to include knowledge, natural resources, and human capacity, and at the same time learn to share each of those more fairly. If we do this, then there is no limit to what humans can achieve together."

Hawking, 74, who was diagnosed with amyotrophic lateral sclerosis at 21, is best known for his work regarding black holes, notes Biography.com, and his life was the subject of the 2014 movie "The Theory of Everything."

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