Are falling sperm counts really an ‘existential threat’ for humanity? Rachel E. Gross The decline has been called a ‘canary in the coal mine’ - Getty Images/iStockphoto Male scientists have long waxed poetic on the contents of their testes. “Sperm is a drop of brain,” wrote the ancient Greek writer Diogenes Laertius. Leonardo da Vinci drew the penis with a sperm duct that connected directly to the spinal cord. The 17th-century microscopist Antonie van Leeuwenhoek claimed that each sperm cell contained within it a folded-up human being waiting patiently to unfurl. For nearly as long, scientists have fretted about sperm’s seemingly inevitable decline. Most recently, a series of alarming headlines – as well as a new book by an public health researcher at Mount Sinai Medical Centre in New York – warned that falling sperm counts might threaten the future of the human race. “It’s a global existential crisis,” says Shanna H Swan, author of the book