Nate,

Of course there is evidence of private property 400 years ago and way further back. The ships that Columbus sailed were “owned” as private property. When a man goes into the forest and fashioned a tool it became his private property. The native Americans used various mediums of exchange such as wampum (c. 1510) for trade. Below is non-exhaustive list of mediums of exchange.

9000 - 6000 B.C.: Cattle. ...

1200 B.C.: Cowrie Shells. ...

1000 B.C.: First Metal Money and Coins. ...

500 B.C.: Modern Coinage. ...

118 B.C.: Leather Money. ...

A.D. 800 - 900: The Nose. ...

806: Paper Currency.

Private property’s existence should not be in question. Rather, when did civilizations start to respect the ownership of private property is the better question.