Critics of the Book of Mormon claim that the Book of Mormon is not a believable work because of the large number of descendants from Lehi and Ishmael’s combined families. James E. Smith compared the Book of Mormon account with other ancient civilizations, using the renowned Cambridge model he helped create for estimating historical populations. Smith believes that the population numbers in the Book of Mormon narrative—though on the high end of scientific estimations—are reasonable. It is possible that the Nephites had a higher fertility rate than Smith assumed for his estimates of their population. Furthermore, it is probable that the Nephites or Lamanites actually absorbed populations that are not mentioned in the narrative. (See Echoes, 130–131.)