An inordinate fondness for sperm.

Sperm are the most diverse and variable of all cells. This is bizarre: all sperm have the same basic goal - to fertilise an egg - so why should they vary so much in shape, size and motion? The answer is that females shape sperm. A co-evolutionary arms race exists between males and females. In evolutionary short-hand, males simply want fertilisations; females on the other hand want to keep males, or rather their sperm at arms length and retain control over fertilisation. The idea that these conflicting evolutionary pressures are responsible for the shape of sperm will be discussed.