"A “right” is a moral principle defining and sanctioning a man’s freedom of action in a social context. There is only one fundamental right (all the others are its consequences or corollaries): a man’s right to his own life. Life is a process of self- sustaining and self-generated action; the right to life means the right to engage in self-sustaining and self-generated action-which means: the freedom to take all the actions required by the nature of a rational being for the support, the furtherance, the fulfillment and the enjoyment of his own life. (Such is the meaning of the right to life, liberty and the pursuit of happiness.)
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The Declaration of Independence stated that men “are endowed by their Creator with certain unalienable rights.” Whether one believes that man is the product of a Creator or of nature, the issue of man’s origin does not alter the fact that he is an entity of a specific kind—a rational being—that he cannot function successfully under coercion, and that rights are a necessary condition of his particular mode of survival." Ayn Rand - Man's Rights
An atheist, and she did not argue that rights come from man. She states that they are a fact of nature.
"But where does nature come from?" "But where does God come from?" - Here we go. ;-)
Speaking of nature, the following is a good essay and should explain why it is wrong to call Rand an libertarian... The Nature of Government
If you all agree that the initiation of physical force is wrong, then you all have something in common.
The initiation of physical force. Who was the initiator again?