sentences:  Hurd conducted a study on digit ratios suggesting a positive correlation in males between aggressive tendency and the ratio of the lengths of the ring finger to his index finger.These gathered significant media attention, being reported on the BBC, in the "New York Times", "Discover Magazine", "Scientific American Mind", "National Geographic" and on Jay Leno.Some of Hurd's most cited papers deal with the evolution of mating displays, specifically the idea that sexually selected traits have evolved to exploit previously existing biases in the sensory, or recognition, systems of their receivers, rather than being handicapped displays Hurd has argued against the handicap principle view of animal communication, demonstrating the evolutionary stability of conventional (non-handicap) threat displays using game theoretical models.