It's interesting to look at the history of patents to get a sense of perspective on the fluidity of property rights. Before the reign of James I, for instance, all kinds of things received patents, not just inventions. Even commodities as common as salt or pepper were patented. The king would grant these patents, implicitly getting the political support and backing from the recipient. It took an act of Parliament (itself a power grab) to end this practice, which is where a new version of patents--applicable only to a new discovery or invention--was legislated.

These patents of yore were pretty alien to us--they represent something more like a government appointment to a role than anything else.