Quoting from https://en.wikipedia.org/wiki/Reproductive_rights :

> Reproductive rights began to develop as a subset of human rights at the United Nation's 1968 International Conference on Human Rights.[4] The resulting non binding Proclamation of Teheran was the first international document to recognize one of these rights when it stated that: "Parents have a basic human right to determine freely and responsibly the number and the spacing of their children."

To answer your question of where those rights come, they come from a international agreement that these principles should be the guide to a human and humane culture. More about this is available from https://en.wikipedia.org/wiki/Natural_and_legal_rights . I think it's best to consider this a moral philosophy that exists only as part of a consensual reality.

Regarding animal rights, there is less agreement on a framework for how to handle those. Animals cannot enter into a social charter, and it is difficult for them to voice objection about mistreatment. Most about this is available from https://en.wikipedia.org/wiki/Animal_rights .

> "Why can we outlaw incest when you have a fundamental right to reproduce."

These rights are not absolutes but exist in tension. While we have agreed that there is a fundamental right to free speech, time, place and manner restrictions are allowed. While we have agreed that there is freedom of movement, such freedom may be limited in times of quarantine.

Thus, simply pointing out that there is a restriction on the right of reproduction does not make it less of a right than the rights of movement and of free speech.

> if reproduction is a fundamental right, can you rape other humans

ryanwaggoner was likely being brief on the expectation that you could do some research yourself and determine that 'Reproduction is a natural right' is a short-hand for a more lengthy and nuanced definition. Quoting now from the Cairo Programme of Action at https://en.wikipedia.org/wiki/Reproductive_rights#Cairo_Prog... :

> Reproductive health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity, in all matters relating to the reproductive system and its functions and processes. Reproductive health therefore implies that people are able to have a satisfying and safe sex life and that they have the capability to reproduce and the freedom to decide if, when and how often to do so.

You can see that the 'freedom to decide if, when and how often to do so' includes all participants. Thus, rape is not part of the right to reproduce, as it is generally understood.

Rape is also in tension with other rights, such as the right to free association.

> "... absolute rights are a god given thing and period"

Humans created all the gods. Therefore humans can create human rights.

> "Could you still come up with the same ideas if you were the only human on earth?"

Human rights guide how humans should be treated. If I were the only human on earth, there would be no need for the moral philosophy of human rights, just like there would be no need for thespian, oratory, or square dancing knowledge. I doubt I would be clever enough to come up with those ideas on my own.