Why do the president, member of congress and fedral judges take an oath to defend the constiution of the united states?

An oath of office is an oath or affirmation a person takes before undertaking the duties of an office, usually a position in government or within a religious body, although such oaths are sometimes required of officers of other organizations. ... The word 'oath' and the phrase 'I swear' refer to a solemn vow.

During the paleolithic, hominins grouped together in small societies such as bands, and subsisted by gathering  plants  and fishing, hunting or scavenging wild  animals. the paleolithic is characterized by the use of knapped stone tools, although at the time humans also used  wood  and bone tools.