How giant bacteria stretch constraints

[A veridically metaphorical explanation of why you shouldn't naïvely cram your life with local optimizations (even for noble or altruistic reasons).]

TL;DR: You need Slack to be an effective agent. Slack is fragile, and it is tempting to myopically sacrifice it, and myopic sacrifice makes future myopic sacrificing more likely. Learn not to do this and cultivate slack.

Slack in Cells

The smallest living mammal is the Etruscan shrew, weighing about 1.8g ("as much as a paperclip"), and ~4cm in length. When curled up, it fits on a post stamp. The largest living mammal is the blue whale, weighing ~100 tons, and about 24 meters on average. Its aorta is so large that a human newborn could fit into it.[1]

Taking those two species as the lower and upper bounds of the mammalian range, we see that they are separated by orders of magnitude in length and orders of magnitude in mass.

Interestingly, this is very close to the 9 orders of magnitude that span the size of bacterial cells, as measured by volume.

Here are two plots from Evolutionary tradeoffs in cellular composition across diverse bacteria by Kempes et al.

[Description from the article:] (a) The volume-dependent scaling of [...]

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Outline:

(00:36) Slack in Cells

(06:48) Slack in Brains

(08:12) Slack is Fragile

The original text contained 5 footnotes which were omitted from this narration.

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First published:
March 30th, 2026

Source:
https://www.lesswrong.com/posts/nQd64RC5vXyqiFZLD/slack-in-cells-slack-in-brains

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Narrated by TYPE III AUDIO.

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