We all know that individuals fight over potential love interests. Just think of Daniel Cleaver (Hugh Grant) and Mark Darcy (Colin Firth) scuffling – rather impotently – over Bridget Jones in a fountain. But you might be surprised to hear that the fierce rivalry continues behind the scenes – in the form of sperm competition. This is when the sperm of two or more males compete inside the reproductive tract of a female, to fertilise the eggs, something that is widespread in the animal kingdom.