to need to ward off threats. They also do not possess adequate defenses to back up the warning pattern. The social function hypothesis states that stripes serve a role in intraspecific or individual recognition, social bonding, mutual grooming or a signal of fitness. Charles Darwin wrote in 1871 that "a female zebra would not admit the addresses of a male ass until he was painted so as to resemble a zebra" while Wallace stated in 1871 that: "The stripes therefore may be of use by enabling stragglers to distinguish their fellows at a distance". Regarding species and individual identification, zebras have limited range overlap with each other and horses can recognise each other using visual communication. In addition, no correlation has been found between striping and social behaviour or group numbers among equines, and no link has been found between fitness and striping. The thermoregulatory hypothesis suggests that stripes help to control a zebra's body temperature. In 1971, biologist H. A. Baldwin noted that heat would be absorbed by the black stripes and reflected by the white ones. In 1990, zoologist Desmond Morris suggested that the stripes create cooling convection currents. A 2019 study supported this, finding that where the faster air currents of the warmer black stripes meet those of the white, air swirls form. The researchers also concluded that during the hottest times of the day, zebras erect the black hair to release heat from the skin and flatten it to retain heat when it gets cooler. Larison and colleagues (2015) determined that environmental temperature is a strong predictor for zebra striping patterns. Others have found no evidence that zebras have lower body temperatures than other ungulates whose habitat they share, or that striping correlates with temperature. A 2018 experimental study which dressed water-filled metal barrels in horse, zebra and cattle hides concluded that the zebra stripes had no effect on thermoregulation. The fly protection hypothesis holds that the stripes deter blood-sucking flies. Horse flies, in particular, spread diseases that are lethal to equines such as African horse sickness, equine influenza, equine infectious anemia and trypanosomiasis. In addition, zebra hair is about as long as the mouthparts of these flies. This hypothesis is the most strongly supported by the evidence. It was found that flies preferred landing on solidly coloured surfaces over those with black-and-white striped patterns in 1930 by biologist R. Harris, and this was proposed to