At this point I'm almost forced to call you intellectually dishonest!
Just finish off that tid-bit of quote you pulled, and you'll find they specify exactly where they come from — a Creator. Whether or not you believe in a Creator might determine whether you reject natural rights, but for those of us that aren't so quick to reject God, then there's a sound basis for believing in them.
"We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness."