A Unified Theory of Animal Locomotion

Roland Piquepaille writes "You probably already know that there is a master equation for all life processes based on metabolism. Now, physicists from Duke University have applied the so-called 'constructal theory' to explain how running, flying and swimming modes of locomotion are similar even if they're apparently unrelated. This single unifying physics theory explains how fast animals get from one place to another and how rapidly and forcefully they step, flap or paddle in relation to their mass. In other words, these scientists argue that the characteristics of animal shape and locomotion are predictable from physics."

Roland Piquepaille

[Anonymous Coward]

Roland Piquepaille and Slashdot [slashdot.org]

Swimming Fish = Flying Bird?

[jackb_guppy]

This is question I have asked my daughter from time to thing about... Are Bird and Fish the same or different?

This article starts to show that yes they are.

For me thought the answer is yes they are. They both can move 3 dimentally in they fuild mediums... Air and Water. Just one is just more dense then the other.

Best example of this is Penguin. They "fly" in water.

Re:Swimming Fish = Flying Bird?

[Akaihiryuu]

Stingrays "fly" in water too (I mean the larger kind that have "wings", not the smaller ones that look like fish frisbees). They are very interesting to watch. They're also very curious...they don't act like fish at all. They act more like puppies than fish actually.

Re:Some solutions missing.

[Jeremi]

If such methods are better, why has no animal evolved them?

It could be just "bad luck" -- evolution isn't guaranteed to find the best solution to anything, only a solution that is "good enough" to guarantee survival of the species (otherwise the species would have gone extinct). But putting that aside, there are probably structural reasons why animals never evolved wheels -- for example, how would do you connect nerves or blood vessels to an appendage that needs to be able to rotate freely?

Finally, it could be that in nature wheels aren't actually "better" after all. There wouldn't be much use in being able to roll down a freeway at 50MPH if there are no freeways, and your snazzy evolved bio-wheels keep getting stuck in the mud...

It seems like the most important thing said...

[gbutler69]

...in this article is, "...with a given gravity and density of their tissues, the same basic patterns of their design would evolve again."

This is important because it would suggest that were humans ever to travel to an "Earth-like" planet, we would likely find life-forms that would appear quite familiar to us. We would not likely find "exotic" life-forms that were nothing like what we'd seen before.

Re:Swimming Fish = Flying Bird?

[Deadstick]

No. Fish receive most of their vertical support from hydrostatic buoyancy; if a fish doesn't move a muscle, it will neither rise nor sink very quickly. All the muscular energy it expends goes into overcoming the drag that resists its forward movement.

Birds have to expend some energy just to stay aloft, plus more to travel. If a bird doesn't move a muscle, assuming it's holding its wings in the gliding position, it will continuously lose altitude. Its drag has two components: parasite drag which resists its forward motion and induced drag which results from the lift-producing process.

When a penguin (or other diving bird) swims underwater, it has to expend energy just to avoid floating up, because it's positively buoyant in water -- in effect, it's flying upside down.

rj

Re:Some robot guys already discovered that

[qray]

Actually, it's what you'd expect. Animals would naturally evolve to move in an efficient manner.

I be they were pretty funny to watch before they started moving in an efficient manner.

Watching my dog chase its tail gives me a glimpse of what it must have been like.
--
Q

Re:Swimming Fish = Flying Bird?

[aussie_a]

Land animals have to do a lot more work than them in order to move in anything but the "plane" of the Earth.

But they can still do it (for instance moving down through the ground can be easier then moving up, but in some cases it can be easier to move up then down, and near cliffs or other walls it is just as easy to move up or down, then it is to move forward or side to side).

Dinosaurs

[samkass]

I'm curious what his equations would reveal about dinosaur locomotion. I've seen a lot of people claim that dinosaurs could never move under today's Earth gravity, or that pterodactyls could never fly. Wouldn't this guy's equations tell us not only whether or not they could, but how fast they'd likely travel and what they're walking, swimming, and flying capabilities might have been?

Did you read the actual article?

[wass]

Good God this article, posted at Duke university, is at the intellectual level of a 5 year old. In print and in person, seems like people are getting really dumb.

However, it's not as 'dumb' as someone mistaking a press release for the actual scholarly scientific article.

I didn't find a link to the article in the press release, and I'm too lazy to bother searching through the journal's Table of Contents to find the authors to get the appropriate link to the article itself, so instead I'll cut and paste the relevent part from the press release.

"The findings, published in the January 2006 issue of The Journal of Experimental Biology, challenge the notion that fundamental differences between apparently unrelated forms of locomotion exist."

Re:Swimming Fish = Flying Bird?

[EvanED]

It does seem like there's a qualitative difference in how they move. You yourself argued in other threads [slashdot.org] that the motions of a bird and fish are different than a mole, because the latter digs. I would add to your distinction the observation that the holes left behind by a mole are permanent in the short term, while the "holes" behind the bird and the fish refill pretty much instantly.

You can take this point further and say that once a mole digs out a nice house, almost all his motion is constrained to the tunnels that are already dug. So while he has the capability to exercise full 3D motion, the natural state is that he does not. And more than that, even if he does keep digging just so that he can prove that he can go in any direction, he'll eventually make a cavern. At that point his 3D control has been lost, as he can't go up without refilling his home.

None of these apply to the bird or the fish. Their motion is, to a large extent, not constrained. Look at the paths of either; they don't go in the same motion. There's no loss of control once they have flown a particular route, nor is there any factor to make them fly that exact route again. And the constraints that the DO face, for instance trees in the case of a bird, have parallels in the mole universe: they can't dig through rocks for instance.

Yeah, but do you think...

[MacDork]

that would be enough to assist a 5 oz. bird carrying a 1 lb. coconut to Mercia? ;-)

So did some computer graphics guys

[Pseudonym]

Famously, Pixar's first film Luxo Jr is based on the same principle. They set up the armature, and then did a global optimisation process to minimise the energy expended for the lamps to hop around.

(BTW, for the would-be pedants present: André & Wally B was not technically a Pixar film, since it was made while everyone was still at Lucasfilm.)