Dogs urinate by leaving messages through urine marks. In addition to the need of physiological excretion, dog urination can also be used to mark territory. Dogs are territorial-conscious animals, and will swear sovereignty to other similar animals by urinating to persuade them to avoid. Dogs also pee when they are in heat to attract the opposite sex. Dogs are domesticated by wolves. As early as the era of hunting and gathering, people have domesticated dogs as hunting assistants. So dogs are the earliest domesticated domestic animals. Dog bones have been found in Cishan, Wu 'an, Hebei, Peiligang, Xinzheng, Henan and Hemudu, Yuyao, Zhejiang, which proves that it has a long history of domestication.