there is- the time it takes to raise our children, humans take the longest time of any animal to do this (that is from birth to total independence)
the reason for this is a combination of our intelligence and our bipedal nature, babies need to be born relatively premature compared to quadrupedal mammals in order to account for a larger brained animal with less room to leave (because of the bipedal effect on hips). hence they're totally helpless- look at any of the common farmyard animals, their kids are up and walking within hours if not minutes of birth.
so as a societal thing, our kids need much more care, and if someone needs to care for the kid they need someone to care for them, and hence the family unit is born. then mix in a bit of religion for a couple of hundred years and bingo- a monogamous biased society.