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I gave to this book to G in 2003; I just re-read that exact copy. It's a neat book about... I'm not sure how to summarize it. The first chapter is about standard cube-square scaling laws as applied to animal size, and why elephants are shaped differently from antelopes. But most of the rest of the book is about warm vs. cold bloodedness, to which scaling is one but not the only issue. Were dinosaurs warm blooded, or something in between; why there aren't more 'in between' animals; why warm bloods dominate large fauna on land and in the oceans; why cold bloods dominate rivers and are (or were before humans) prominent in Australia.

Very small animals are all cold blood, because warm can't eat enough and keep enough heat at that scale. Small animals are split; hiding is a good strategy, being warm has high costs, the world is more complex and has more niches at a small scale. Hiding doesn't work well for big animals, who are also driven to a simpler 2D world, so being ready for action has very high value and warm bloods dominate... unless food is so uncertain that you get long intervals of not eating, as in rivers or Australia.

Also river ecology is complex and poorly understood. Naked mole rats are practically cold blooded mammals, protected by their tunnels and living in very marginal areas, where the food tends to be a limited number of large roots. Ostritches used to span a wide area, like Greece, Moldavia, and China.

There's also discussion of how warm bloodedness evolved in the first place, given the high costs. Answer, we don't know, but there are a couple theories. One is that some ancient large animals in stable climates were mass homeotherms, with fairly stable temperatures even without working at it, so they optimized their enzymes to adapt to that (enzymes have narrow ranges of optimal performance; lots of organisms have more genes than humans probably because they needs lot of alternative cellular biochemistry), then when some branch shrank again, it was easier to invent warm bloodedness rather than re-invent a whole slew of enzymes.

The other idea is that boosted aerobic performance is beneficial by itself, and eventually some animals were boosted enough that they were significantly warm blooded as a side effect. This feels less elegant to me, but Lavers said it was favored at the time of writing.

The last chapter is on global mixing of species, thanks to human transport, and making a worrying analogy with the Permian mass extinction, which followed mixing (supercontinent) and global warming (massive volcanism, probably.)

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Damien Sullivan

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