One of the biggest challenges for human beings in the next two decades will be the lack of more human beings, according to Alibaba Chairman Jack Ma and Tesla CEO Elon Musk.

The billionaire techpreneurs met on one stage at the World Artificial Intelligence (AI) Conference in Shanghai on Thursday to debate the power of AI and the future of computers.

Ma believes artificial intelligence poses no threat to humanity, claiming that compared to humans, computers are just a toy. The best resource in the world is the human brain, he says, explaining: “It’s impossible that humans could be controlled by machines. They’re machines that are invented by humans.”

Musk disagreed with Ma, noting that computers are getting smarter than humans in more and more spheres and that the trend will continue. “We will be far, far surpassed in every single way. I guarantee it,” he said to Ma. He pointed to advances in chess and the Chinese board game of Go as evidence of progress in AI, saying “Your cell phone could crush the world champion of chess, literally.”

Arguing his point, the Tesla and SpaceX founder said humans are capable of creating things that are superior to people. Humans are not the last step in evolution, Musk suggested, warning that people must be wary of thinking that they are smarter than they really are. “The most important mistake smart people make is that they think they’re smart. Computers are already smarter than people. We just keep moving the goalposts,” he said.

Ma, who seemed at times to be bored or puzzled by Musk’s comments, as he frequently pulled pained expressions and raised eyebrows, disagreed with his opponent’s statements.

“Computers may be clever, but human beings are much smarter,” Ma repeated. “We invented the computer – I’ve never seen a computer invent a human being.”

According to the e-commerce giant founder, AI will open a new chapter so that humans will know themselves better. “Most of the projections about AI are wrong … people who are street-smart about AI are not scared by it.”

While insisting that he is “not a tech guy,” Ma added: “I think AI can help us understand humans better. I don’t think it’s a threat.”

Musk countered: “I don’t know man, that’s like, famous last words.”

Ma said he believes that with AI’s help, humans could eventually reach a point where the average workweek is only 3 days long, and the workday averages 4 hours. That opens the opportunity for humans to enjoy life more, and live longer, he said, adding: “We need to be ready to enter the era where everyone will get to live [to] 120 years.”