During an interview with the CEO of Insider's parent company, Musk revealed three "existential threats."

The richest man in the world said he fears religious extremism, a declining birthrate, and artificial intelligence going wrong.

Musk said that the birthrate may be the biggest threat to the future of human civilization.

Musk has long flagged his concerns of the declining birth rate, a trend that has accelerated amid the baby boom.

Musk said he was worried about the birthrate thing. It is worse every year. I drive my friends crazy with this.

The fear of not having enough babies ranked high on Musk's list, but the fear of dying did not.

I would like to stay healthy for a longer period of time, but I am not afraid of dying. I think it would be a relief, he would like to live long enough to see the full realization of the project.

Several of the world's billionaires are looking to discover the scientific fountain of youth. Musk doesn't want to increase the human lifespan.

I don't think we should try to have people live for a long time.

The government has lost touch with the average person due to the age gap between politicians and the majority of the population, according to Musk.

Most people don't change their minds. They die. We will be stuck with old ideas if they don't die.

Musk said his greatest hope is for humanity to create a self-sustaining city on Mars.

He said that he would be happy if humanity had a city on Mars. We don't want this small candle in the dark to go out.

Musk has goals for the future of humankind, but his feelings about personal happiness are less clear-cut.

I think it's important to be happy at work and happy in love. He said that he was medium happy. Earlier this month, Musk split from a singer after welcoming a second child.