One wonders here if the original text read “and were devoured by those beasts and also by the vultures of the air”. The reading in 𝓟 seems rather awkward without any repeated by. One might propose that a repeated by was accidentally lost in the early transmission of the text. Evidence in support of this possibility can be found later on in the text. In the following passage, the repeated preposition by has been accidentally deleted at least once, perhaps twice, in the transmission of the text:
For this part of the text (from Helaman 13 through the end of Mormon), the 1830 edition was set from the original manuscript. And in the 1830 edition we have the repeated by (“by angels and also by the voice of the Lord”). On the other hand, the printer’s manuscript is missing the repeated by, which suggests the possibility that Oliver Cowdery, when he copied from 𝓞 into 𝓟, accidentally omitted the repeated by in 3 Nephi 7:15. Of course, the opposite possibility must be kept in mind: the 1830 typesetter could have added the by because the phraseology “by angels and also the voice of the Lord” was awkward. Interestingly, we do know that the repeated by was accidentally omitted by the typesetter for the 1849 LDS edition. His copytext, the 1841 British edition, had the repeated by. Subsequent LDS editions have continued with the reading without the repeated by, thus unintentionally maintaining the reading of the printer’s manuscript.
Elsewhere the Book of Mormon text repeats the preposition by in conjuncts that have also:
Only in the case of Alma 2:38 is the by not repeated when the conjunct has also. Since we know that the 1849 LDS edition omitted the repeated by in 3 Nephi 7:15, the same error could have occurred in the early transmission of Alma 2:38. Clearly, both Alma 2:38 and 3 Nephi 7:15 read much better when the by is repeated.
There is considerable evidence that scribes and printers have had difficulty maintaining the repeated by, although in all the following examples there is no also in the conjunct:
Moreover, it is probably the case that in 3 Nephi 7:15 the omitted by in 𝓟 is the result of Oliver Cowdery once more accidentally omitting the repeated by (see under that passage for a complete discussion). For another example where a repeated preposition after and also—one different than by—has been omitted, see Alma 18:36, which originally read “he began to the creation of the world and also to the creation of Adam” (the 1837 edition omitted the repeated to). Thus we can see that there is a good chance here in Alma 2:38 that the lack of a repeated by in the conjunctive phrase “by those beasts and also the vultures of the air” is the result of a loss of the by early on in the transmission of the text, perhaps in 𝓞 itself since Oliver did not supply the by when he proofed 𝓟 against 𝓞.
Ultimately the question becomes just how important the occurrence of an also is to the repetition of a preposition. In over 90 percent of the cases involving and also, the preposition is repeated (or there is an equivalent preposition, such as to for unto). But in six cases in the earliest text, there is no repeated preposition. Besides the example here in Alma 2:38 (where the by is not repeated), we have these examples involving other prepositions:
These examples suggest that it is not necessary for the preposition to be repeated after and also. The critical text will therefore maintain the earliest (and current) reading for Alma 2:38—that is, without the repeated preposition (“and were devoured by those beasts and also the vultures of the air”). It is quite possible that the original text had a repeated by here and that it was lost early in the transmission of the text. But it is also worth noting that there has been no tendency to add the preposition in any of the cases where it is not repeated.
Summary: Maintain in Alma 2:38 the reading without the repetition of the preposition by after and also (“and were devoured by those beasts and also the vultures of the air”); despite its awkwardness, such phraseology without the repeated preposition after and also is occasionally found in the earliest text.