Matthew Cobb takes us back to 1677, when Anton Van Leewenhoek first identified sperm and there was much talk of souls and miniature men residing in the seminal fluid. Upon observation it became clear that there were an awful lot of those little guys that never turned into babies! Jad wonders: why so many sperm? Bird-sex specialist Tim Birkhead, of the University of Sheffield, explains what effect imperfect monogamy has on reproductive strategies. Then sperm physiologist Joanna Ellington and her pig Hazel give us some insight into the obstacles sperm must overcome in their odyssey from their male originator to their female destination.