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July 2nd, 2018

even Heinlein nods

I just picked up and reread The Rolling Stones, one of Heinlein's juveniles for Scribner's, and to my taste one of the best. One of its better known episodes is the "flat cat" episode, where the Stone family acquire a Martian animal called a flat cat, a pancake-shaped furry animal that attaches itself to hosts, snuggles against them, and purrs. After 64 days, it gives birth parthenogenically to eight flat kittens; after another 64 days they have kittens; and after 64 more days those kittens have kittens—and Heinlein says there are 513 kittens.

Now, we start with 1 flat cat. The next generation is 8; the third is 64; and the fourth is 512. But the sum of those numbers is 585. The number Heinlein gives is the sum of the first and last generations, implying that the intermediate generations died—which he doesn't mention and presumably didn't mean to have happen.

And there's a deeper point than that. If Fuzzy Britches had had another litter when her kittens had kittens, that would have been 9 flat cats giving birth to 72 kittens, for a total of 81; and if they all had kittens, it would have been 648 kittens, for a total of 729. So it appears that each flat cat had only one litter. That's certainly a possible life history—but it makes no sense for an animal that reproduces once to go on living afterward, apparently indefinitely. Certainly the flat cats should die by the time their kittens reproduce, and they could very well die right after giving birth, as there's no mention of nursing or other parental care. But Heinlein doesn't show any of them as dying. So really, the numbers ought to have been even higher!

Heinlein liked to put explanations of how vital it is to study mathematics into his juveniles, and The Rolling Stones has one, early on. It's ironic to find him miscalculating a simple geometric series expansion!

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