How human sperm really swim: research challenges centuries-old assumption

A breakthrough in fertility science by researchers from Bristol and Mexico has shattered the universally accepted view of how sperm 'swim'. "However, our discovery shows sperm have developed a swimming technique to compensate for their lop-sidedness and in doing so have ingeniously solved a mathematical puzzle at a microscopic scale: by creating symmetry out of asymmetry," said Dr Gadelha. "The otter-like spinning of human sperm is however complex: the sperm head spins at the same time that the sperm tail rotates around the swimming direction. This is known in physics as precession, much like when the orbits of Earth and Mars precess around the sun." Computer-assisted semen analysis systems in use today, both in clinics and for research, still use 2D views to look at sperm movement. Therefore, like Leeuwenhoek's first microscope, they are still prone to this illusion of symmetry while assessing semen quality. This discovery, with its novel use of 3D microscope technology combined with mathematics, may provide fresh hope for unlocking the secrets of human reproduction. "With over half of infertility caused by male factors, understanding the human sperm tail is fundamental to developing future diagnostic tools to identify unhealthy sperm," adds Dr Gadelha, whose work has previously revealed the biomechanics of sperm bendiness and the precise rhythmic tendencies that characterise how a sperm moves forward.