“You’re pretty small,” she said. “You should probably take a large.”
At five feet, nine inches, I tend to weigh in between 160 and 170 pounds. To my mind, that’s decidedly average. But I had to admit that, in a relative sense, her oxymoron was apt: Both I and the large T-shirt I wound up buying were at the bantam end of the conference’s attendees.
I don’t often weigh in on public health issues, but the weird symmetry between a pair of completely unrelated publications really brought the topic of size, as well as that story, to mind recently.
First, in a recent British Medical Journal article, the common wisdom that wolfing down your food makes you more likely to over-eat gained some support. Hrioyasu Iso and crew at Osaka University reported that people who reported that they ate meals quickly were about twice as likely to be overweight as those who said they didn’t. Those who reported eating until they were full were, similarly, twice as likely to tip the scales. If you do both, you’ve got thrice the chance of being overweight.
The idea is pretty simple: Your body has to digest some of the food you’ve eaten to be able to sense that you’ve eaten it. If you wolf it down, your body’s satiation doesn’t catch up with the intake, and you overshoot. Amazingly enough, the fast, full eaters even outdid binge eaters — whom the Osakans analyzed separately — in total calories consumed.
True, any result that assumes people tell the truth when you ask them to report about themselves needs confirmation by another method — but it sure seems credible.
Well, imagine my surprise when, the very next day, I caught a strangely reminiscent Perspectives article in Science by P. Martin Sander and Marcus Clauss at the universities of Bonn and Zurich. Their paper discussed the latest findings on what allowed giant sauropod dinosaurs like Apatosaurus and Brachiosaurus to supersize themselves.
Can you see this one coming? They didn’t stop to chew their food.
Here’s the conceptual problem with these animals’ overly ample size: mammals, such as elephants and the extinct Paraceratherium, can and could get pretty big. So could other, distantly related dinosaurs, such as the duck-billed Shantungosaurus and the perennial favorite, Triceratops (these are all vegetarians, BTW; we’ll get to the carnivores shortly). Interestingly enough, this set of giants tops out at roughly 10 to 20 metric tons. But the sauropods were literally in a class of their own, with masses up to 80 metric tons.
Sauropods got that large for a number of reasons: But one primitive feature — a characteristic they shared with the species they evolved from but not necessarily later species – seems to be the enabling issue. Namely, the fact that they neither chewed their food (their jaws were relatively tiny and weak, their teeth designed for clipping rather than chewing) nor ground it up internally with a crop or rumen.
See, if you’re going to swallow leaves, twigs, and whole branches without grinding them up, you need to give them a lot of time to digest. And that requires a big, huge stomach, which slows digestion to the required rate even if you’re shoveling it in. (Which, if you’re going to grow to 80 tonnes, seems de rigueur.)
’Course, if you are going to grow that large, you need to get hold of food that other animals can’t. Hence the long neck, which would be a huge vulnerability if you weren’t big enough to crush the predators. And an anatomical impossibility if you didn’t have a relatively tiny head: that, in turn, possible because as you have no need to chew, you require no heavy jaw musculature or skeletal structures in your head. Nicely synergistic, no?
One other primitive feature played into the sauropods’ vast size: Big mammals can’t get much bigger, in part, because raising a small number of large, live-borne offspring would be ruinously expensive; since sauropods laid many eggs, they sidestepped this issue. Add the one decidedly modern sauropod characteristic (one that they didn’t share with ancestor species), a bird-like respiratory system that can actually get air down that long windpipe, and it all sounds like a body plan.
And the top predators? Well, they tend to be smaller than their prey, to avoid a metabolic pyramid scheme. But the Jurassic period (when sauropods flourished), and the Cretaceous (when they were present but much less predominant), grew their meat-eaters big, too (think Allosaurus and Tyrannosaurus, vs. the more “normal,” dog-sized Velociraptor). Sander and Clauss suggest that all them herbivore eggs were the reason: Lots of offspring for the veggies meant lots of food for the carnies, while still letting enough of the prey survive to feed the next generation of jabberwockies.
Lest you think I’ve dropped my original thread: Apatosaurus got to its huge size a bite at a time, and so have we. Check out the U.S. data between 1960 and 2002 for adults age 20-29, when we’re supposed to be young and skinny:
Source: U.S. National Center for Health Statistics, Mean Body Weight, Height, and Body Mass Index, United States 1960-2002. Advance Data No. 347. 18 pp. (PHS 2005-1250).
Holy crap. I guess we’d better start chewing.