We belong, to speak plainly, to a species of animals which nature intends to be monogamous and monandrous.    From Wordnik.com.  [Freeland A Social Anticipation] Reference

For man is by nature a monogamous and monandrous being; polygamy and polyandry are inconsistent with the fundamental characteristics of his nature; they are diseases of civilisation which would vanish spontaneously with a return to the healthy conditions of existence.    From Wordnik.com.  [Freeland A Social Anticipation] Reference