Antoine R. Ivins questions whether modern Lamanites are universally descended from Laman and Lemuel.
Antoine R. Ivins, "The Lamanites," Relief Society Magazine 37, no. 8 (August 1950): 507–508
I feel that we are not justified in believing that all of the people who rallied to the banner of the Lamanites were actually descended from Laman and Lemuel or that all who called themselves Nephites were the actual descendants of Nephi, Sam, or the faithful sons of Nephi. The term Nephite soon came to mean the faithful, while the term Lamanite meant unfaithful people.
After the battle of Cumorah, the Lamanites were left in control, and it appears that there was but one faithful man left of the Nephites. To him we are indebted for the Book of Mormon, which tells us this story.
Because of this account, we are in the habit of thinking all of the indigenous groups who were upon the land of the Americas when Christopher Columbus landed here, as Lamanites. I wonder if we are justified in this assumption.
. . .
The Book of Mormon tells us of the Jaredites, the Mulekites, and Lehi's family. The Mulekites lived for years near the Nephites before they were discovered by the latter. There may have been other peoples whom the Nephites never discovered living then on this great land, or, as suggested, others may have come later. The very wide differentiation in the languages of the native races of the Americas would seem to indicate this possibility.
. . .
Whether all of these indigenous peoples were descended from Lehi matters little. For the purposes of this short article we shall refer to them all jointly as Lamanites.