Unusually high ratio of Levites to Firstborn-Levites

Question

Near the beginning of the Book of Numbers (from roughly 3:39 to 3:51), G-d commands that all the firstborn Israelite males need to be redeemed via a 1:1 'trade' with a Levite. There were 22,000 eligible Levites, with the remaining 273 Israelite firstborns redeeming themselves via a monetary payment.

Rashi on verse 3:39 questions why weren't there enough Levites, when the counts from the individual Levite families totaled 22,300 Levites. He answers (based on a Gemara in Bechoros) that there were 300 Levites who themselves were firstborn, and therefore inelligible to partake in the redemption of the Israelite firstborn, since they were 'redeeming themselves'.

While the narrative is straightforward, what strikes me as interesting is the ratio between firstborn Levites and 'standard' Levites. With 22,300 Levites and 300 of them being firstborn, that comes out to less than 1 in 70 Levites being a firstborn. That seems like an unusually low number of firstborns to me (or on the flip side, an unusually high number of non-firstborns)! Do any of the commentators address this seemingly unusual ratio?

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A few side points based on comments and other thoughts:

• While we are dealing only with male firstborn, assuming a relatively equal percent of male and female children, even if the numbers double the ratio should remain the same.
• The total number of non-Levite males comes out to a bit over 600k, per Numbers 1:45-46. That gives the ratio for non-Levites to be around 1 in 28. Much less than 1 in 70. It is worth noting that the total counts are only those aged 20 and older, while the firstborn count began at 1 month (per Numbers 3:43). However, even if you double the number of non-Levite non-firstborns (which seems generous, IMO, should probably be ~50% more at most), you would still have a lower ratio than the Levites (a difference of about 20 in the denominator).
• There is a Midrash (quoted in Rashi on Exodus 1:7) that Jewish women were regularly birthing sextuplets. That may account for an unusually high ratio, although the Levite ratio being higher would not be explained by this alone. It is also worth noting that some opinions say that the Levites were not included in this blessing, since it was a 'compensation' for being enslaved in Egypt and the Levites were not included in the subjugation (the ArtScroll Stone Chumash brings this down according to Rashi). According to this opinion, it would strengthen the question, as the Levite ratio should be significantly lower than than the non-Levite ratio.
• It is unclear what Halachic parameters were used here to determine 'Firstborn'. Obviously, standard Pidyon Haben rules weren't followed exactly, as by definition that would preclude Levites from being involved at all. Perhaps there was some unique combination of Halachos and familial makeup here that contributed to the ratio.

Answer 1

I am unaware of any classical commentators who address this question. However, I know of 3 different approaches that have emerged in recent years:

1. Some cite the midrash about each birth in Mitzrayim being sextuplets. That would mean the average family would be six times larger than normal. (I'm not sure if this fully answers the question, but it certainly is a step in the right direction.)

2. Others, including Prof. Eliyahu Beller of Bar Ilan, answer that these are only the firstborns who were born after Makas Bechorot. Notably, the Ramban mentions this idea and rejects it.

3. Prof. Joshua Berman, also from Bar Ilan, in his book "Ani Maamin", argues that the census numbers in the Torah are not intended as literal, and brings the number of firstborns, along with several other internal pieces of evidence, as proof.

Answer 2

Genesis 46:8 "And these are the names of the children of Israel who were coming to Egypt: Jacob and his sons Jacob's firstborn was Reuben."1

Israel had 12 sons (from 4 different women) and yet only 1 of these sons were considered "firstborn". So, if a Levite had four wives, and if that wife that bore the firstborn had more sons, and the other wives also had scores of sons, then it is indeed possible to have "an unusually low number of firstborns" as the OP surmises.

Answer 3

The question is really even stronger. Besides the Levites, the general population had 603,500 from ages 20 to 60 with only 22,270 firstborn sons and that was counting from the age of 30 days! Assuming that every 20 years is 300,000 male adults (obviously later generations would be more but at a minimum it would be 300,000) that means the ratio for the general population is approx. 1:40 which is baffling in of itself. Moreover, any answer to these questions need to take into account the difference between Levites and the rest of the population. Why would Levites have bigger families?

One idea that can possibly help clarify is the killing of the boys during the exile by Pharoh. Perhaps many firstborns were killed then, only boys not girls. Additionaly, the Levites did not work in Egypt while the rest of the Israelites did, which may have contributed to their larger family sizes. Including the idea of sextuplets may also help however many of those children should of been over 60 by now as that was around the time of the birth of Moshe Rabbeinu.