Is marriage an artificial concept that has come into existence just because the life expectancy of humans is around 60 years. What if the life expectancy was 200 years or say just 15 years. Would we still have the concept of marriage in humans?

I rather expect that monogamous marriage is more the result of the agricultural revolution than an artifact of our life spans. It was when we changed from hunter-gatherers to "property-owners" (so that we could raise our crops and lay claim to the fruits of our agricultural labors), I suspect, that someone got the brilliant idea that we could own not only land and what it produces, but also start building private homes (since farmers don't need to keep moving around to hunt and gather) and having private families. That was when we began to "own" other people--including slaves, spouses, and children. In many early versions, this "ownership" was strictly one-way: it was not adultery (or a violation of marriage) for a man to have sex with some woman who was not owned by someone else (either as wife or daughter, for example), but was a violation of marriage if the wife engaged in such extra-marital activity.

The institution has changed as human society has changed, but I still think it is an artifact of another age in this sense. That does not mean it does not still have value. On the other hand, it does strike me as quite plausible to think that we would not have this institution if our average life span was only fifteen years. But then I think other problems would arise (e.g. for survival of our species).

You might extend your speculations in other interesting ways, by the way: What if the average life expectancy of only females was 15, but for males it was about what it is now in the US, for example? Or what if it was the other way around, with males being very short-lived and females having 80 years? But anyway, I agree with the thrust of your question, which is that there is no "natural necessity" in this social arrangement, as we know it.

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