New York (AFP) – Elon Musk said Thursday that he was helping combat falling birth rates after it was reported that he had twins last year with an executive at one of his companies. “Doing my best to help the underpopulation crisis,” tweeted the billionaire tech entrepreneur, who has fathered 10 children. “A collapsing birth rate is the biggest danger civilization faces by far,” Musk added. He posted another tweet that read: “I hope you have big families and congrats to those who already do!” The comments came a day after online outlet Insider reported that Musk had twins with 36-year-old Canad…