Thank you for your clarification. I was under the mistaken assumption that you were interested in alternatives to monogamous marriage, eg, might be poly-curious. Instead, you were questioning the existence of marriage. For that you will have to look towards cultural anthropology. A quick search shows finds, for example, http://www.oxfordbibliographies.com/view/document/obo-978019...

> Over the years as well, anthropologists have debated what lies at the very core of marriage as an institution and as a relationship, whether it is economic sharing, sexual access, childbearing and parenthood, or reproductive success. They also have debated whether marriage is best described in terms of sentiment and subjectivity, social or mental structures, or transactions and strategic choice.

That is far outside of my depth. I can recommend looking at countries which have both formal marriage arrangements and less formal cohabitation laws to see some of the benefits of having a legal recognition. For example, https://www.island.is/en/family/marriage_and_partners/co_hab... says that "rights of cohabitating people are affected by whether their cohabitation is registered or not", so they exist even without formal recognition, and "Individuals in cohabitation do not bear any responsibility for each other's financial support, and do not have the right of inheritance towards one another".

As an example of the latter, from http://hhogman.se/cohabitation.htm , "Stieg Larsson, the renowned Swedish writer who lived sambo for many years with Eva Gabrielsson. When he died in 2004, his father and brother, not Eva, inherited his wealth worth millions. There were law suits and a settlement, but this could have been avoided with a will."

See also https://edition.cnn.com/travel/article/wonder-list-bill-weir... for one US citizen's view about marriage, or the lack thereof, in Iceland.

Regarding "formal legal marriage seems to be largely for the benefit of the state so they can tax and interfere with lives of citizens".

Given my quote from earlier, your hypothesis does not sound correct. As an example, the medieval Icelandic state deliberately avoided having a strong centralized state. Your hypothesis would suggest that this would mean there was no need for marriage, yet we know from the sagas that there was marriage. See for example https://digitalcommons.wou.edu/cgi/viewcontent.cgi?article=1... , which includes descriptions of marriage in pre-Christianity Iceland.

Here is one thing that would change if we magically forget the concept of marriage tomorrow. If the next day I have a medical condition which renders me unconscious, who has the right to make medical decisions for me? I am married, so under the current legal system my spouse - someone I voluntarily decided to marry, and who best knows my opinions - has the first option. Not my family-by-blood, as that relationship wasn't voluntary.

Here's another - who has the right to visit me when I'm in the hospital?

These can all be addressed without marriage, but the result is still some sort of registration system, with some sort of arbitration system to decide how to manage conflicts. Which is close to what cohabitation systems are already like.

I cannot conjecture on Heinlein's purpose in writing Friday. It may be addressed better in some of the references I gave earlier.

Regarding again "dedicated to the questions of what defines gender", I think he did so within a binary gender essentialist viewpoint. I don't think he was 'fearless' in examining what the larger topic of what it means to be queer. The example I quoted about transvestites is one of the few in Heinlein's works. In his later novels, name one character who is asexual. 'Slipstick' Libby was a man who became a women, but her transition was nothing like what trans-women now experience.

My comments were not so inadvertent, in that you mentioned your pet theory in recent comments of your, which I reviewed before responding. However, I don't believe that your use of the terms "mutant", and the terms "male" and "female" for zygotes, have much biological meaning, and certainly not once we get into culturally-defined gender.

I also don't think your use of "faulty" has any biological meaning but is your personal interpretation. No system which has been around for 100+ million years can be described as "faulty". Monotremes don't have the SRY gene but do have males and females. The XY system also evolved several times, including in "some insects (Drosophila), some snakes, and some plants (Ginkgo)." It's further believed to have evolved from the temperature-dependent sex determination system of reptiles, meaning that male/female distinction is far older than the Y chromosome.