獸人的由來？

[Bagheera]

日本跟歐美的獸人定義完全不同.
各自有各自系統

Incorrect. The definition is quite the same, although the translation is what misleads people.

In Lord of the Rings, the race of the Orcs are translated into Chinese as 獸人; this is incorrect, and Orc by itself is just a name Tolkien invented.

獸人 in Japan is called "Anthros" in English, as it is widely known in the furry communities here.

獸人 does have a long history - many ancient mythologies (Mayans, Greeks, etc.) all have half-man half-animal creatures. However, the modern phenomenom of groups of people who likes 獸人 probabaly started in the 1960's. I believe there were people who like animal people before 1960's, but keep in mind that because people before 1960's were more Conservative, and communications were less easy (lack of Internet, etc.), people who like 獸人 were isolated and alone.

After the Liberal movements in the 1960's, followed by things like Satellite communications and the Internet, people from all around the world who like 獸人 can meet each other.