Humans also have incredibly long childhoods.
Whether you favor evolutionary-biology or God's Plan as the cause, the two observations stack: Humans would not be able to accumulate and pass on technology without the long period of child/parent interactions and mothers would not be able to raise children without a second adult---specifically a man---bonded to her.
Sex is the sticky side of the duct tape. Sex is what holds couples together.
Biology and culture are not to be trifled with.