The large ears of a jackrabbit (hare) might be adorable, but they're also functional: a large network of blood vessels running through the ears allows a hare to regulate body temperature as needed. If a hare is too cold, these blood vessels constrict to conserve body heat. If the outside temperature is above the hare's internal temperature, the blood vessels dilate, increasing their surface-area-to-volume ratio and encouraging heat loss. By regulating body temperature through their ears, the desert-dwelling hares are able to conserve water, because they don't lose moisture through sweating or panting.
Elephants also use their ears for temperature regulation. Elephants flap their ears like fans, helping cool the blood flowing through the vessels in their ears. Between the flapping and the thin skin, blood moving through the ears can cool by as much as 14 degrees Fahrenheit. To magnify the effect, elephants also will spray water on their ears.
In 2012, Stanford biologists H. Craig Heller and Dennis Grahn released a device that used similar methods to cool human skin. The cooling glove works by pulling blood vessels in the hands closer to the surface of the skin and then cooling them down via cold air circulating through the glove. The device, the researchers say, could be used to help ease muscle fatigue during exercise.