More Words, Deeper Hole

Ok, I will absolutely not, under any circumstances, argue that it isn't more complicted than what we've been squabbling over. No, you are absolutely correct that it isn't necessarily a simple ratio. Yes, I was deliberately arguing it on a simple level, though. But I have to admit, your arguments about scaling laws: I'd be stupid to try to dispute all that. You make good points. Although there is something nagging at the back of my mind -- I'll have to let it stew in its own juices for a bit before the thought gels, though.

I think, in the first instance, I was simply having a knee-jerk reaction to the notion that the hyena and capybara are pretty much on par with each other-- they aren't, and I will stick by that.

Of course, when you consider relative neocortex size, cortical folding (which I personally have an interest in, although I haven't had the opportunity to explore that interest to any detailed degree) and all the other fun modular aspects of brain evolution, the arguments can get complicated indeed. (Any idea how much cortical folding a capybara has? Frankly, if they have much more than their cousin the cavy I would be vastly surprised.) But anyway, when you say "brain size is only a loose correlate for functional intelligence", yeah, no argument. It's a base measure. It's a starting point. There are obvious points where the general correlation breaks down (for instance, I would suggest that marsupials fall off the small end because so much of their gestation ends up being ex utero, given that most placental mammal brain growth takes place in utero; on the other end, I don't have the reference to hand but I believe there is a "minimum mammal brain size" so that very tiny mammals, like the smallest species of mice, have a lot more brain for their mass than you would expect). ...But it is a rough measure, against which you would expect relatively bigger-brained critters to generally be functionally more intelligent than smaller brained ones. (Enough caveats?)

(Of course, once you move outside mammals you do run into MAJOR problems with that; look at all the recent papers on the cognitive abilities of corvids! I'm just talking mammals, above.)

...lineage is also strongly correlated with lifestyle. Upshot: one can't make the simple claim that a predatory member of Carnivora will have a larger brain at the same body mass as a herbivore of Rodentia because it's a predator. It might have a larger brain because it's a member of Carnivora.

I don't know if you were paying any attention to my argument with Doug M., below, but that was precisely my basis for asserting that "social complexity" is a valid driver of brain size even though it is not a perfect correlate with brain size in orang-utans -- given that orangs are primates (and arboreal, come to that), and primates hit the top end of the scale in general. And that a relatively nonsocial species with a big brain does not invalidate the hypothesis of social complexity as a driver for brain size, given that there are strong arguments that social living is an ancestral primate trait which was partially lost in orangs, but this didn't automatically correlate to a loss in inherited brain size. (Not to mention all the confounding factors: arboreal vs. terrestrial, diet, etc.)

Anyway, I think we have a better idea of where we each stand, anyway. I don't think I disagree with you that much. ;-)