Many adaptations serve more than one function. This is often the reason some traits become so noticeable that they almost define the species concerned. The legs of a horse are also a main defence: a horse's kick is very destructive. The antlers of male deer serve a sexual function as well as a defence against predators. Man's large brain serves not only for language, but also for thinking and problem-solving. Bird feathers are not just used to fly; they are the basis of its heat conservation, temperature regulation and signalling