Sperms swim faster toward attractive females

The study, published in Proceeding of the Royal Society B, is based on tests of red junglefowl, an ancestor of chickens. Scientists found that males allocated larger ejaculates to attractive females, which can be easily identified by the comb, reportedDiscovery. 

African cichlid fish proved the theory as males produce more energetic sperms because females mate with males in quick succession. Australian scientist John Fitzpatrick of the University of Western Australia, who led the fish study, put it this way — "Just like a mechanic could make a car drive faster by installing a better engine, evolution appears to act first on the engine that drives sperm movement." 

Scientists hope future research will help them figure out how males adjust the sperm and seminal fluid in their ejaculates, and how this affects fertility rates.