Beard-stoking

The Scientist has a big ol' article, with a fine typo in the last paragraph, on West, Brown, Enquist and their metabolic theory. It's particularly good on recent historical and biographical detail, although a little sketchier on how the idea works, and what else it might apply to besides metabolism.

And I would take issue with the statement that temperature is a "variable necessary to explain the 3/4 scaling of metabolic rates across organisms". It's not, it's an additional variable that explains some of the variation in metabolic rates (between say, reptiles, birds, and mammals, all of which have different body temperatures) not accounted for by size-based 3/4-power scaling.

The article also shows how some of the disagreements about the theory come from differing expectations and goals. WBE are after a theory that gives an abstract, approximate, first-order account of the underlying structure of organisms and ecosystems.

Confronted with Helen Muller-Landau's data on forest population biology that contradicts their predictions they say, well, ok, it shows something else must be going on. Much as, if you see a planet that doesn't follow its predict orbit, you look for something else influencing it before you junk gravity (not that I am saying metabolic theory is as well-established as gravity). Muller-Landau and others, however, see deviation as disproof.

It's a difference partly of philosophy. But it also shows the genuine uncertainty about when you decide that just because a theory can't predict everything doesn't mean it's wrong (as Michael Ruse has written, natural selection's failures are a sign of its strength), and when you decide it's wrong.

WBE's metabolic model is too powerfully predictive, and its foundations make too good sense, to be junked yet. In fact, it seems to be popping up more and more - I have recently spoken to fisheries and foodweb researchers who are using it.

I would also say that people tend not to change their minds, regardless of what data or theory say. A scientific field's centre of gravity depends on when people retire and who gets their job, as much as it does on dialectic.

(The Scientist has published a couple of previous things on metabolic scaling and so on: here and here.)

Sleep and metabolic rate

Update: the link to the paper is now working. Duh. Sorry.

Sleep is another of those biological phenomena of which we lack a good theoretical understanding, despite there being lots and lots of (good) hypotheses and experiments. Van Savage and Geoff West have suggested a first step to building one, though. And (wouldn't you know it) it's based around metabolic rate.

The amount of time a mammal spends asleep, they find, is proportional to their relative, or cellular, metabolic rate. A fast-burner like a mouse sleeps for about 14 hours a day, whereas an elephant kips for only 3.5 hours. What's cool is that they find that sleep time is most closely matched to the brain's metabolic rate. Their suggestion is that sleep duration corresponds to the amount of time needed either repair brain cells, or reorganize them to process the day's input.

So unlike other organs, perhaps you need to shut down the (conscious) brain to maintain it. Fast-celled animals need more time for repairs (which, if this model holds, seems a more likely function of sleep - or at least of metabolically related sleep - than reorganization), because they do more damage while they're awake. The same argument applies to why small animals have shorter lifespans - fast cells, more free-radical damage, shorter lives.

What's that Lassie? A lot in life seems to depend on metabolic rate? Perhaps by understanding metabolic rate we can inch towards some kind of powerful, simple theory to explain a wide range of biology? You wish someone had written an accessible guide to this vibrant field and its long and strange history? Well, girl, it's your lucky day.