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...
In writing these words, the Declaration's author, Thomas Jefferson (1743-1826), was to some extent merely paraphrasing the words of the English philosopher John Locke (1632-1704), who wrote in his Second Treatise on Government:
Reason..,.teaches all Mankind...that being all equal and independent, no one ought to harm another in his Life, Health, Liberty, or Possessions. For Men being all the workmanship of one Omnipotent, and infinitely wise Maker...are his Property...made to last during his, not one [another's] Pleasure (Chapter 2, Paragraph 6).
Note that Jefferson and Locke both link human equality and human rights to a Creator, that is, God. For both Jefferson and Locke, all human beings are equal and have certain rights because they are the "workmanship" (to use Locke's words) of God.
However, is it really true that "these truths" that Jefferson wrote of are "self-evident"? For an atheist, the answer would have to be "no," since by definition an atheist rejects the existence of a Creator. Thus, it cannot be a "self-evident" truth for an atheist that the equality of all human beings and human rights derive from God.
In fact, one of the most famous atheists in history, Karl Marx, completely rejected the concept of universal human rights. In their article "Was Karl Marx Truly Against Human Rights?", Justine Lacroix and Jean-Yves Panchere write of:
...the young Marx's diatribe against human rights, which he reduces to the "rights of egoistic man, to man as a member of bourgeoisie society, that is to say an individual separated from his community and solely concerned with his self-interest." These alleged universal rights of the abstract individual would in reality promote the interest of one social type: the possessive individual of capitalism.
Lacroix and Panchere do note that at least one scholar has questioned the view that Marx rejected the notion of human rights on the grounds that Marx's perspective on human rights has to be understood in its context. Nevertheless, they argue that "it is not certain...that placing greater emphasis on context suffices to dispel the critique of human rights delivered by the young Marx, a critique which he never revisits and that his later writing radicalized."
Of course, not all atheists would agree with Marx's rejection of the concept of human rights. Nevertheless, it seems to me that those who do accept the notion of universal human rights face this question: on what basis do human beings have rights? Atheists generally hold to the view that human beings are the result of a long, unguided process of evolution. However, evolution, being only a process, could not have conferred rights on human beings. Nor could Nature, since Nature is merely an abstraction. Other possibilities could be proposed, but fundamentally it is difficult to explain why human beings have rights if those rights have not been bestowed on them by a Creator.
In short, the ringing words of the Declaration of Independence about "self-evident" truths can only be rhetoric for an atheist. Please note that I am not saying that an atheist cannot believe in human rights, but only that he or she has no logically compelling reason for doing so. His or her belief may be quite sincere, but that belief would be logically inconsistent with atheism.
Image of Thomas Jefferson (portrait by Rembrandt Peale) from Wikimedia Commons