My housemates and I had a party not long ago.
And shortly after I began reading a book by Richard Dawkins. It says, in the realm of evolutionary biology, absolutely no way mate does altruism exists for the benefit of group selection. Risking your life for your mates is just not happening, evolutionarily that is. Unless… instead of risking your life for your mates, you do it for your family. And by risking your life, you actually just do it so that your family, who share a part of your selfish self, live long enough to steam up the car windows and have some kids. Making sure that your genes are succeeded. It’s called The Selfish Gene.
So why does anyone have house parties? Your house gets trashed, your neighbours stop lending you cups of sugar, someone steals your booze and you spend the next 3 days picking up ciggie butts. Why not wait for someone else to have a party instead? That way you can pour flat beer on the fiddle leaf fig, piss in the front yard and put your general waste in the recycling.