London Size does not matter when it comes to a sperm’s ability to reach and fertilise an egg, a study published today suggests.

Research in the London-based journal BMC Evolutionary Biology casts doubt on the common scientific belief that sperm with longer tails can swim faster. The speed at which a sperm swims is a key factor in its capability to fertilise an egg.

While a longer tail does mean more thrust, this can be cancelled out by the drag caused by a correspondingly larger head. The proportions of the sperm - and ratio of head size to tail length - is the key factor, the researchers found.

Stuart Humphries, from the University of Sheffield, who took part in the study with collaborators from the University of Western Australia, said: “It is commonly believed that selection for increased sperm performance will favour the evolution of longer sperm. In fact, the relative lengths of a sperm’s parts, rather than their absolute lengths, are likely to be the target of selection.” The authors added that looking at liquid dynamics could allow research to progress rapidly.

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