Historian: Slavery undoubtedly preceded racial discrimination in the United States. As Africans began to be imported in the English colonies, the colonial legislatures started to relax the terms of service and the options for freedom for the then-indentured white servants to incentivize more English servants to migrate to the colonies. The African laborers were not covered under such placatory legislation, and could be enslaved - that is, indentured for life without an option of freedom; therefore, they came to be the preferred choice of the taskmasters for the lowest-status and, therefore, the least desirable jobs. Due to this permanent association with menial jobs, they gradually came to be seen as naturally inferior people.
Which of the following, if true, most strengthens the historian's assertion about the relationship between racial discrimination and American slavery?