Behind their graceful appearance, giraffes hide a body that can weigh 1,500 kg and especially measure 5.8 m high. Their  size is based on the presence of long forelimbs and a  disproportionately large neck, yet composed of 7 cervical vertebrae, as  in most mammals. The properties of this region of the body would have been acquired during evolution by natural selection. 

 The long neck of giraffes, a preserved genetic mutation

In the past, random genetic mutations may have caused the appearance of giraffes with abnormally large necks compared to normal. The  advantage is obvious: these individuals were able to reach food  sources, for example branches of acacia, unexploited by other animals  because out of reach. No longer having to fight for food, long-necked giraffes could live longer and reproduce more easily. They gradually settled from generation to generation, while specimens struggling with other species gradually disappeared.