The Evolution of Monogamy in Gibbons

The siamang is to mammals what frogs are to amphibians. They have a throat sack like a frog that they can inflate before singing, using the resultant space to create more resonance. This sack of theirs can expand to the size of their own head. Simanks typically reproduce every few years. A fully running simang family will consist of two parents and then a few offspring. That's not a natural thing in humans.