Apart from the myth and fantasy portrayed in society through media projection, does selflessness and sincerity in men-women relationship (which idealistically ended up in marriage) really exist in reality?
It exists, just not in most couples.
Men-women relationship (and ultimately; marriage) is driven by our subconscious primitive animal instinct. It never is about selflessness and sincerity, it is all about the gratification of our selfish inner desire.
Incorrect. Marriage is a construct of a civilized society. Marriage as an institution does not exist on a genetic level. Basically our animal instincts do not drive us to marry because love/romanticism does not exist within a state of nature. Speaking from an animalistic standpoint, our only drive is to mate which we could easily do by raping. Marriage implies rules, restrictions, and the like, before one is able to pass on their genes. Marriage as an institution is counter-productive to the animalistic approach to mating. Therefore marriage, as an institution is not driven by animal instinct.
And that's an overgeneralization right there. Subconscious primitive animal instinct may not be sincere and selfless, but it's not selfish either.
He's been doing that A LOT lately.
The instinct drove us to search for companionship, therefore ultimately it is driven by our individual needs - thus the selfishness.
That's a sad way to look at things. Not everything is driven by selfishness just because you think it is. One of our individual needs is to breathe. Does breathing make us selfish? One of our individual needs is to eat. Does the act of eating, on its own, imply that we're selfish? And please, do not attempt to amuse me by going on a tangent about stealing food, pillaging, or what have you. Does eating, as a stand alone act imply selfishness? No of course not. Preservation of the self, of the race does often come at a cost to others, but the act of self-preservation by itself is nothing selfish.
To make my point even further, in finding our consort - we always create a set of criteria that satisfy our desire - so once again, where is the sincerity and selflessness?
I don't even have enough time to explain everything that is wrong with this statement so I will summarize.
1) You're overgeneralizing, again.
2) Some men look for women with big boobs, most women look for men with money. Why? A woman with big boobs is suited for nursing just as a man with money is suited to providing for his family. The respective sex looks for qualities in their opposite which would contribute to the survival of their next genetic line. Given how much you advocate nature, genetics, and evolution I wouldn't think I have to explain this.
3) Another issue with your argument is that you do not take into account those marriages in which one or neither party is getting married to satisfy his or her desire. I'm referring to arranged marriages in which it is not uncommon for couples to marry for no other reason than being forced into it by their families.