Oh, they could well have assumed it was some type of supernatural person, even the traditional Christian God. I'm saying the derivation of our individual rights works just as well if "our Creator" was a purely natural process. The essential part is the fact that we are endowed with individual rights, that are inalienable because they are directly implied from our intrinsic nature as human beings. How, precisely, we came to be human beings (with minds capable of complex abstract thought) instead of just large monkeys (for whom any abstract concept such as "rights" is far beyond their mental reach) is irrelevant to that issue.