Polygamy had been introduced early, though it was contrary to God’s plan. The Lord gave one wife to Adam, but after the fall people chose to follow their own sinful desires. As a result, crime and misery increased rapidly. Neither marriage nor the rights of property were respected. People reveled in violence. They delighted in destroying animals, and the use of flesh for food made them still more cruel and bloodthirsty, until they came to regard human life with indifference. BOE 36.1
The world was in its infancy, yet evil had become so deep and widespread that God said, “I will destroy man whom I have created from the face of the earth.” He declared that His Spirit would not always strive with the guilty race. If they did not cease their sins He would blot them from His creation; He would sweep away the beasts and the vegetation that furnished such an abundant supply of food and would transform the fair earth into one vast scene of ruin. BOE 36.2