Elon Musk laid out a blunt set of productivity rules for Tesla employees in 2018Elon Musk has once again raised concerns about falling birth rates and population decline, saying he has been warning about the issue for years. The Tesla and SpaceX CEO was responding to an X (formerly Twitter) post that claimed 2026 could be the first year in human history when the world's overall fertility rate falls below the replacement level. “People don’t realize this, but 2026 appears to be the first year in human history where humanity as a whole is below replacement fertility. this has never happened before. not during wars. not during pandemics,” X user wrote in the post. The user called the trend an existential crisis, prompting Elon Musk to reply: “I’ve been warning about this for years.”Musk has repeatedly described falling birth rates as one of the biggest long-term threats facing civilisation. His latest comments come as fertility rates continue to fall in many countries and several nations have already reached peak population and begun to decline.What the data says about global fertilityThe latest data shows that fertility rates have fallen sharply across the world. Our World in Data, using UN projections, says the global fertility rate was around 2.2 children per woman in 2025, close to the commonly used replacement level of 2.1 children per woman. Many countries are already below that level.However, the claim that humanity as a whole is already below replacement fertility in 2026 should be treated with caution. Available estimates and projections differ, and the world's population is still growing. The UN expects global population growth to slow further and projects the world's population to peak later this century before eventually declining.Countries including China have already seen their populations peak and begin to decline, largely because of long-term falls in fertility.What Elon Musk has said about population declineElon Musk has been speaking about the issue for several years. In 2022, he wrote that “a collapsing birth rate is the biggest danger civilization faces, by far.” He has also previously said that population collapse caused by low birth rates could pose a greater risk to civilisation than climate change.More recently, Musk commented on India's falling fertility rate. In June 2026, he wrote: “India’s birth rate has fallen below replacement. Among those most educated, India’s birth rate fell below replacement many years ago.”