The research team includes Stuart Humphries, from the University of Sheffield, and collaborators from the University of Western Australia have critically evaluated the evidence linking sperm shape to swimming speed. The study showed that longer tail does allow a sperm to generate more thrust but the drag created by a sperm's head is often enough to counteract any such gains.
"It seems clear that some assumptions regarding the physics of sperm locomotion have hampered our progress in understanding the processes mediating sperm competition," said Humphries. "It is commonly believed that selection for increased sperm performance will favour the evolution of longer, and therefore faster swimming, sperm. "In fact, the relative lengths of a sperm's constituent parts, rather than their absolute lengths, are likely to be the target of selection," he added.[an error occurred while processing this directive]
"We suggest that, irrespective of whether tail length, total length or head length is used, and any attempts to correlate a single measure of length to speed are likely to be futile. "We argue that accounting for the balance between drag from the head and thrust from the tail will allow us to extend our understanding of the link between sperm form and function," he added.