The Spirits' Book
Book Three - Moral Laws
Chapter IV - III. Law of Reproduction
701. Is polygamy or monogamy more in compliance with the laws of nature?
“Polygamy is a human invention, the rejection of which marks an era of social progress. God intended that marriage should be based on the existence of true affection between the individuals who enter into it. In polygamy there is only sensuality, but no real affection.”
If polygamy were consistent with the laws of nature, it would be possible to institute it everywhere. However, it would be physically impossible to do so, due to the numerical equality of men and women.
Therefore, polygamy must be labeled a social custom, adapted to the circumstances of specific nations or populations. It will gradually disappear as these populations improve socially.