Two or more could perform the family tasks much better.

Thus a man who could pay the customary price would be inclined to add a second wife, whom the first would probably welcome as a lightener of her burdens.

Polygamy prevailed almost everywhere.
Slavery, too, was generally prevalent except among the few tribes who gained their chief sustenance from hunting.

Along with polygamy, it perhaps originated, if it ever had a distinct beginning, from the desire to lighten and improve the domestic service.

[3] Persons became slaves through capture, debt or malfeasance, or through the inheritance of the status.
While the ownership was absolute in the eyes of the law and captives were often treated with great cruelty, slaves born in the locality were generally regarded as members of their owner's family and were shown much consideration.