Parsha Analysis: Why So Few First Born?

I admit this topic would have been more relevant to the Torah reading of two weeks ago (Parshas Bo), but I was inspired by a related posting yesterday in Maven Yavin. In his article there, lamedzayin provides a mathematical analysis of how the 70 individuals who came to Egypt with Jacob could have grown, in a span of only 210 years, to 600,000 adult males - implying a total population of at least 1.5 million. LZ demonstrates convincingly that given a new generation born every 20 years or so, and with just a moderately high birth rate comparable to that in the developing world today (even leaving out a literal view of the midrash about every woman having sextuplets), the population would easily have grown to a couple of million or higher in that time.

A similar question, which my father and I discussed many years ago, was why there are so few bechorim [male first born] in proportion to the total number of people. As per the counts given in Bamidbar (Numbers), there were about 22,000 bechorim and, as stated above, 1.5M total population. Assuming a male child was born first about 50% of the time, this would imply that only about one in 34 children was a bechor. And the existence of polygamy doesn't help here, since a bechor is defined as first born of the mother.

The theory we came up with was very straightforward. Namely, the reason there are so few bechorim at the time of the Exodus is that many Jewish first born died during makkas bechoros [the 10th plague]. After all, the Torah never says that Jews as a group were unaffected by that plague, as in fact it does state for several of the other plagues. Rather, it provides a conditional: those Jews that put the blood on their doors would have their first born spared. Quite possibly, many families ignored this requirement and their first born died, thus leaving relatively few bechorim per capita.

Although I have never seen this theory in any of the meforshim [classical commentaries] , the concept that Jews were not necessarily immune to makkas bechoros is implied by the famous statement in the haggadah shel pesach concerning the rasha [wicked son]. We are told that "if he were there, he would have not been redeemed". This is odd, for we know that many known reshaim were in fact redeemed from Egypt - e.g., Korach, Dathan, Aviram. However, the particular sin of this rasha was scoffing at, and excluding himself from, the Passover ritual. Therefore, if he were there, he would have refused to put the blood on his door and would have been lost during makkas bechoros!