After Elon Musk spoke to Neuralink director Shivon Zilis about his population decline fears, she decided to have children. He suggested being her sperm donor.

• Elon Musk and Shivon Zilis decided to have children together after he spoke to her about population decline.
• The tech mogul and Zilis, currently a Neuralink manager, had twins in November 2021.

Elon Musk and Neuralink manager Shivon Zilis decided to have children together after the tech mogul spoke to her about his population doomsday fears, according to a new biography.

Musk and Zilis had twins, born in November 2021. Their births were kept quiet until Insider reported on them in July 2022.

Zilis told biographer Walter Isaacson that she had decided not to get married, but that she had "the motherhood bug super hard."

This was intensified after Musk told her about his concerns about declining birth rates leading to human population collapse, Isaacson wrote.

"He really wants smart people to have kids, so he encouraged me to," Zilis told Isaacson.

When Zilis decided she was ready to have children, Musk suggested that he could be the sperm donor.

"If the choice is between an anonymous sperm donor or doing it with the person you admire most in the world, for me that was a pretty fucking easy decision," Zilis told Isaacson. "I can't possibly think of genes I would prefer for my children."

"It seemed like something that would make him happy," she added.

The twins were conceived by IVF and Zilis did not tell people that Musk was the father, Isaacson wrote. Even Grimes, the mother of three of Musk's children, didn't find out about the twins until their births were revealed by Insider, according to Isaacson's book.

The twins, born seven weeks prematurely, were named Strider Sekhar Sirius and Azure Astra Alice.

They were born just a few weeks before a surrogate mother gave birth to Musk's daughter with Grimes, Exa Dark Sideræl Musk, known as Y. Isaacson wrote that at one point, both Zilis and the surrogate mother, accompanied by Grimes, were unknowingly in the same hospital in Austin with complications with their pregnancies.

Originally the twins took Zilis's last name, but this was later changed to "Musk," with "Zilis" kept as a middle name.

Zilis told Isaacson that she didn't expect Musk to play a very active role in the children's lives. "I thought he would play a role like a godfather because the dude's got a lot going on," she told Isaacson. But he spent a lot of time with the twins, staying over at Zilis's at least once a week and sitting on the floor with them during work video calls, according to the book.

"When he comes in, they light up and have eyes only for him, which lights him up as well," Zilis told Isaacson.

Musk and Zilis originally met through OpenAI, the nonprofit Musk cofounder. In 2017 she became a project director at Tesla, and later moved to Neuralink, where she is currently director of operations and special projects.

Musk and Zilis became close friends and even played games together. She was also friends with Musk's then-girlfriend Grimes, who sometimes tried to arrange dates for her.

"It's been one of the most meaningful friendships of my life, like, by far," Zilis told Isaacson of her friendship with Musk.

"In six years, Elon and I have never, never gotten in a fight, never argued," she added.

In August 2021, she bought a home in Austin, which Zillow estimates is worth more than $4 million, and appeared to move to the city – where Musk also lives – from Silicon Valley. This was just three months before the twins were born.