Interesting (?) question about bipedal locomotion

[Bulldog Psion]

As a combined sci-fi and fantasy geek, I'm sometimes compulsively interested about the weirdest parts and corner cases of fiction.

Disclaimer: I realize you can cover anything, including my current topic, with the explanation "Magic did it." While that's fine, what I want to talk about here is whether a bipedal stance could occur without magic and without being like human bipedalism, in a sapient species.

It looks like dinosaurian bipedalism would be adapted to sapience, since it frees up the hands for manipulation of objects, writing, tool use, weapon use, etc.

However, what about something that is basically digitigrade (walks on its toes, like a dog) or unguligrade (horse-like animals)?

Fictional depictions of wolf-folk, for example, often show them with crooked back legs and feet that are walking on the toes. Draenei from World of Warcraft have big clunky hooves at the end of crooked legs.

My question is, in the absence of magic, would all sapient bipedal species tend to evolve legs similar to human legs for the sake of stability, regardless of what their base stock was? (Note that similar does not mean identical -- they could be longer, shorter, with narrower or wider feet, different number of toes, etc. But a plantigrade foot with a knee that bends forward and a leg that is completely straight when standing still.)

The dog-like legs seem highly unstable to me. The hooves seem a little more stable -- at least there's a flat surface on the ground -- but I'm not sure if the crooked leg would remain once a quadrupedal gait was abandoned.

Could a sapient with a human-like straight leg but a hoof on the end evolve? Or is the heel-arch-ball-toe arrangement too advantageous for fine balancing for evolution to ignore it?

Any thoughts?

[Mx.Silver]

Could a sapient with a human-like straight leg but a hoof on the end evolve? Or is the heel-arch-ball-toe arrangement too advantageous for fine balancing for evolution to ignore it?

Any thoughts?

You seem to be coming at this from a bit of a teleological standpoint. Evolution doesn't 'ignore' things, and natural selection only selects for the most advantages trait that's already present in the population. The question you should be asking is whether or not hooves can work, or what modifcations will be needed to improve for bipedal balance.

As to whether its can evolve, the trouble is that hoofed animals don't really gain much by freeing their hands. Being able to balance on the hind legs might be useful for getting a better view, or reaching food (which some gazelle do) but hooves don't lend themselves well to manipulating things.

[Ravens_cry]

They could go the elephant route instead, evolve a different organ into a manipulator. By manipulator I mean any organ or set of organs used as hands and arms are used, without necessarily being hands as we think of them. The beak claw combination of many birds, the tentacles and arms of a squid or octopus, and the aforementioned trunk, are but some possibilities.

[Teddy]

Actually, the dog legs aren't all too unstable, at least not in principle. I'm having trouble with hurting my heels when I walk too much on hard surfaces without wearing shoes with thick and repressive soles. In order to counteract this, I often walk around on my toes when at home, and balance has never been a problem. Sure, I am more unstable this way, but not so significantly that I can't get along, and if you would push me backwards, I'd still have my heels to fall back on.

That said, bipedal wolves would probably either evolve into walking on their heel joints as well in due time, or grow longer toes to provide forward balance.

[hamishspence]

It looks like dinosaurian bipedalism would be adapted to sapience, since it frees up the hands for manipulation of objects, writing, tool use, weapon use, etc.

However, what about something that is basically digitigrade (walks on its toes, like a dog) or unguligrade (horse-like animals)?

Theropod dinosaurs (including birds) are already digitigrade- so I could see "walking on the toes" never actually being lost.

[Bulldog Psion]

Theropod dinosaurs (including birds) are already digitigrade- so I could see "walking on the toes" never actually being lost.

True, I guess I should have said "mammalian digitigrade," since mammal toes tend to be much shorter, and are closely packed, unlike the spreading toes of therapods.

[hamishspence]

Evolution has been known to solve things in rather odd ways- so I'm not sure if "lengthen toes" would be significantly less likely than "become plantigrade".

Though I suppose it does happen more often- bears, for example- a plantigrade creature, a bit more bipedal than its digitigrade ancestors.

[Don Julio Anejo]

One question you may want to answer is whether there is common ancestry between organisms.

Dinosaur feet, human feet and bird claws still have the same basic skeletal frame - several flexible bones radiating forward. This is because the foot has been essentially the same (frog) organ that evolved into its respective counterparts. Sure, there are some differences - birds and dinosaurs (more closely related/on the same phylogenic clade in a tree) have a "thumb" that points back for stability; humans have a flatter foot and toes for the same reason.

If the organisms have a common ancestor, the end result would likely be the same.

Now, on the other hand, if you have a bipedal insect, they might use a completely different scheme. For example, two long flat sticks at an angle to each other (similar to skis) that I'm pretty sure grasshoppers can stand up on.

Hooves (think satyr - human hands and hooved legs) probably won't work, for the reason mentioned above. There is simply no advantage for hooved animals to stand up, and since their front legs can't be used as manipulators, this feature won't be selected for.

And finally, dogs have essentially the same skeletal structure, with modifications for length. I would imagine over the course of millions of years of bipedalism, their foot would turn into something that's more stable, so likely longer and flatter. Not necessarily the same as a human foot, but at least somewhat similar in a perfect case of analogous evolution.

[hamishspence]

And finally, dogs have essentially the same skeletal structure, with modifications for length. I would imagine over the course of millions of years of bipedalism, their foot would turn into something that's more stable, so likely longer and flatter. Not necessarily the same as a human foot, but at least somewhat similar in a perfect case of analogous evolution.

Something like when bears evolved from doglike ancestors.
EDIT- I was sure at first- but it's a bit less clear when I look it up- though if the prototype bear was something like this:

http://en.wikipedia.org/wiki/Hemicyonidae

it may have been digitigrade.

[Ravens_cry]

Evolution has been known to solve things in rather odd ways- so I'm not sure if "lengthen toes" would be significantly less likely than "become plantigrade".

Evolution tends to work with what it has, changing an existing organ than making an entirely new one from scratch. Human style feet are a development of primate feet changed for bipedalism.

[Don Julio Anejo]

Something like when bears evolved from doglike ancestors.
Bears are actually an interesting case in and of themselves: if you look at a bear skeleton without the skull, it would look almost indistinguishable from a human one with really long arms.

[hamishspence]

It's certainly something interesting to think about.

Red Pandas are a very distant relative of common pandas (which are within the bear family) yet both evolved an almost identical "false thumb" for holding bamboo.

[Ravens_cry]

Bears are actually an interesting case in and of themselves: if you look at a bear skeleton without the skull, it would look almost indistinguishable from a human one with really long arms.
I wouldn't say 'almost indistinguishable', but certainly surprisingly similar.

[WarKitty]

One question you may want to answer is whether there is common ancestry between organisms.

Dinosaur feet, human feet and bird claws still have the same basic skeletal frame - several flexible bones radiating forward. This is because the foot has been essentially the same (frog) organ that evolved into its respective counterparts. Sure, there are some differences - birds and dinosaurs (more closely related/on the same phylogenic clade in a tree) have a "thumb" that points back for stability; humans have a flatter foot and toes for the same reason.

If the organisms have a common ancestor, the end result would likely be the same.

Now, on the other hand, if you have a bipedal insect, they might use a completely different scheme. For example, two long flat sticks at an angle to each other (similar to skis) that I'm pretty sure grasshoppers can stand up on.

Hooves (think satyr - human hands and hooved legs) probably won't work, for the reason mentioned above. There is simply no advantage for hooved animals to stand up, and since their front legs can't be used as manipulators, this feature won't be selected for.

And finally, dogs have essentially the same skeletal structure, with modifications for length. I would imagine over the course of millions of years of bipedalism, their foot would turn into something that's more stable, so likely longer and flatter. Not necessarily the same as a human foot, but at least somewhat similar in a perfect case of analogous evolution.

Of course, this also brings up an interesting idea. If the end goal is the use of something akin to hands, there's no reason we couldn't have, say, quadripedal spiderfolk.

[Ravens_cry]

Of course, this also brings up an interesting idea. If the end goal is the use of something akin to hands, there's no reason we couldn't have, say, quadripedal spiderfolk.
So, centauroids.

[Bulldog Psion]

So, basically, the summary of the thread thus far is:

Digitigrade feet work for bipedalism if the toes spread like a bird or dinosaurs, and probably work for mammal-type feet but are likely to evolve into plantigrade feet in that case.

Plantigrade feet are likely for mammalian bipeds even if they are somewhat different from human feet.

No hoofed biped would be likely to evolve naturally, so anything in fiction with an upright stance and hooves would have to result from magic.

Creatures with more than four legs could evolve a centaur-like build to free up two or more limbs to provide tool-manipulating hands.

A quadruped with different manipulators could potentially be a sapient tool-user (though I think that having only a single manipulator, like an elephant's trunk, would be a massive disadvantage, since you would need several creatures to perform even a simple task like driving a nail).

Does that sound about right thus far?

[erikun]

No hoofed biped would be likely to evolve naturally, so anything in fiction with an upright stance and hooves would have to result from magic.
Somewhat. A hooved biped that gained its hooved feet after walking upright (and this had non-hooved "hands") or one a hooved quadruped that had only hooved back legs could possibly evolve into a hooved biped, although both situations would probably be noticably odd. The problem is that a something like a horse would have little use for two limbs with only a single digit.

Also, not all hooved animals (ungulates) are single-toed ungulates. Even-toed ungulates (http://en.wikipedia.org/wiki/Even-toed_ungulate), such as goats, would find freeing up their front limbs much more useful and so are far more likely. There are even odd-toed ungulates which walk on more than one toe, such as tapir (http://en.wikipedia.org/wiki/Tapir) and even rhinoceros (http://en.wikipedia.org/wiki/Rhinoceros) that would get more benefit from having limbs free.


A quadruped with different manipulators could potentially be a sapient tool-user (though I think that having only a single manipulator, like an elephant's trunk, would be a massive disadvantage, since you would need several creatures to perform even a simple task like driving a nail).
It would be a significant disadvantage for an elephant to use a human tool, true. I'm not sure how much of a disadvantage it would be for an elephant to use an elephant-deisgned too, though.

In this hammer-nail example, it would be easy for an elephant to design a nail-holder that can be manipluated with the trunk, and a foot pedal to stomp on to drive the nail.

[hamishspence]

The problem is that a something like a horse would have little use for two limbs with only a single digit.

Multi-digited horses were around till fairly recently:

http://en.wikipedia.org/wiki/Hipparion

[WarKitty]

So, centauroids.

Right. The trouble here would be what the ancestor would be. Some form of insect or spider ancestor seems the most likely, but then you have size issues since exoskeletons don't scale well. It would probably be more likely for a quadraped to evolve bipedalism than extra limbs.

[warty goblin]

Right. The trouble here would be what the ancestor would be. Some form of insect or spider ancestor seems the most likely, but then you have size issues since exoskeletons don't scale well. It would probably be more likely for a quadraped to evolve bipedalism than extra limbs.

If the context is science fiction, there's no reason why you couldn't have a planet where vertebrate analogs evolved with six limbs instead of just the four.

[Ravens_cry]

If the context is science fiction, there's no reason why you couldn't have a planet where vertebrate analogs evolved with six limbs instead of just the four.
Or genetic engineering by intentional actions by other, earlier species.

[warty goblin]

Or genetic engineering by intentional actions by other, earlier species.

That would take some rather hardcore genetic engineering, at least if one starts with Earth stock. Either you'd need to figure out how to code for an embryo developing six limbs instead of four - and get those limbs to have useful and effective musculature which in turn requires knowing what that musculature is - or do some really freaky stuff with insects.

Frogs can develop extra limbs due to chemical or parasite damage to the embryo, so it's not completely out there. I think this is fairly unique to frogs - and certainly to amphibians however.

[Ravens_cry]

That would take some rather hardcore genetic engineering, at least if one starts with Earth stock. Either you'd need to figure out how to code for an embryo developing six limbs instead of four - and get those limbs to have useful and effective musculature which in turn requires knowing what that musculature is - or do some really freaky stuff with insects.

Frogs can develop extra limbs due to chemical or parasite damage to the embryo, so it's not completely out there. I think this is fairly unique to frogs - and certainly to amphibians however.
Not saying it would be easy, but I can see it being doable, especially if genetic engineering moves beyond splicing features from one creature to another and more actual engineering from the ground up.

[warty goblin]

Not saying it would be easy, but I can see it being doable, especially if genetic engineering moves beyond splicing features from one creature to another and more actual engineering from the ground up.

There may also be hard limits on what can be tweaked in any particular species, at least over a reasonable timespan; simply because making large changes to one system throws another fatally out of whack. I remember crossing bantam and fullsize chickens once for instance; about half to two thirds of the hatched chicks died, presumably from non-viable anatomy. There was no evidence of disease, and no more accidents than usual; but the mortality rate was significantly above my previous or later experience. And that's just from two varieties within a species. Trying to add a whole new set of limbs is an entirely different ballgame.

[Ravens_cry]

There may also be hard limits on what can be tweaked in any particular species, at least over a reasonable timespan; simply because making large changes to one system throws another fatally out of whack. I remember crossing bantam and fullsize chickens once for instance; about half to two thirds of the hatched chicks died, presumably from non-viable anatomy. There was no evidence of disease, and no more accidents than usual; but the mortality rate was significantly above my previous or later experience. And that's just from two varieties within a species. Trying to add a whole new set of limbs is an entirely different ballgame.
What is a 'reasonable time span'? A thousand years? How about ten thousand? Given that crossing the distance between stars could in itself take hundreds if not thousands of years with plausible technology, I am assuming any extrasolar modders would be used to playing with long, long times.
Moreover, plausible, if non existent, technologies like artificial wombs could also help speed the process, as, unlike the purely biological variety, they wouldn't reject creatures that are too different from the base creature.

[Don Julio Anejo]

Actually, adding extra limbs wouldn't be all that difficult as long as they're the same as already existing limbs. An organism's structure is encoded by a set of hox genes, and given the way it develops, the embryo would simply grow and expand in more directions. Things like nerves grow along with the organism, it's for this reason siamese twins are viable. There's already a lot of examples with extremely mutated fruitflies. Some even have perfectly working limbs growing out of their eyes.. not for the faint hearted.

It may not happen in the next 20 to 50 years, but as long as you allow for a lot of trial and error (say, on mice), it would be possible.

The problem would be adding things to an organism that it doesn't have. Sticking in human hox genes, even perfectly identified/compensated for a slightly different embryonic system into a horse won't suddenly add arms. More likely you'd have a weird (and possibly dead) hybrid. Same with, say, adding a second heart.

But giving a human 4 arms? Should eventually be possible. I can do some research and address the topic more when I have some spare time in a few weeks, if you guys want.

[Avilan the Grey]

I wouldn't say 'almost indistinguishable', but certainly surprisingly similar.

Not human, but "Primate". Just like the ancient giant ground sloths. Both bear skeletons and sloth skeletons look somewhat like oversized gorillas.

As for feet...

Bears, ferrets (badgers, wolverines, whathave you) all are heel walkers too (like monkeys, apes and humans). Many rodents, racoons and kangaroos too. Cats and dogs are not. It DOES seem a lot of predators and omnivores that do use their front limbs to any degree walk on their heels, probably for balance. As we all know, mice and rats use their hands to actually hold things very well; bears have a far more limited gripping system but have fine control and "arms" that can move sideways for swiping, climbing and gripping and "hugging", and despite having no thumbs at all they can perform very delicate tasks like opening clams without actually cracking the shells.

The key, however, is if it is beneficial for the species to walk, or at least spend significant time, on it's hind legs. Again, both bears and rodents very often stand up on their hind legs. Both seem to do it mainly to just get a good view of things arround them. The smaller members of the ferret family also do this, but not the heavier ones (badgers, wolverines do not, to my knowledge, ever sit up on their hind legs). The more time you spend on your back feet alone, the better they must evolve to keep the balance.

However there are great exceptions, for example all walking birds (including dinosaurs), that walks on their toes.

...And now I realized people have already summed all this up.

[Teddy]

But giving a human 4 arms? Should eventually be possible. I can do some research and address the topic more when I have some spare time in a few weeks, if you guys want.

There are known cases of people being born with an extra leg, so it shouldn't be outside the realm of possibility, no.

[Avilan the Grey]

There are known cases of people being born with an extra leg, so it shouldn't be outside the realm of possibility, no.

Of course the gene must also be dominant and the mutation common enough that the four-armed human can forward his or her mutation to common generations AND that it gives a large enough advantage to eventually overtake the "competition".

On the other hand, human evolution at this stage is hampered by the fact that we don't really want to, or need, to evolve:

Not only do we solve our problems at this stage in our evolution by just building machines that can do it for us, negating the need for an extra arm, or better eyesight, or radar orientation. We also have... taste. A four-armed man might simply not be able to spread his genes because no female wants to mate with him.

...On the other hand... Power Perversion Potential might kick in and EVERY female wants to mate with him... :smallwink::smalltongue:

[thubby]

i would direct the threads attention to the ostrich, it's legs work in the same basic manner as a dog's, having a heel well off the ground running to toes. so it's certainly possible for a biped to have non-humanoid legs.

as for hooves, i would question their ability to exert the fine control necessary on the ground to maintain balance. you don't realize how important all of your toes are when it comes to balance.
draenie at least have cloven hooves so it's more believable.

[Avilan the Grey]

i would direct the threads attention to the ostrich, it's legs work in the same basic manner as a dog's, having a heel well off the ground running to toes. so it's certainly possible for a biped to have non-humanoid legs.

Exactly. All running birds, be it an ostrich, emu or allosaurus run in the same way. On their toes. But note that the toes in that case is significantly wider than on a canine or feline.

When it comes to hooves, the only "model" I deem realistic (because of the sensitivity and fine control) is the camel toe foot. It has actually evolved back from a hard surface to basically soft sandals, and are cloven to boot.

[thubby]

the primary difficulty with something evolving more than 2 arms is just how much more energy it takes to create and maintain a limb compared to the benefit.
if i were determined to create a 6 limbed alien, i would expect something that walked like a gorilla, then had an extra smaller set of limbs for manipulating things delicately.
but it would have to exist in an environment where it was vital that it be able to both hold a thing and manipulate it at the same time. for example, some 6 legged mammal analogue that fought off predators with its central legs while holding with its front ones.

[Don Julio Anejo]

the primary difficulty with something evolving more than 2 arms is just how much more energy it takes to create and maintain a limb compared to the benefit.
if i were determined to create a 6 limbed alien, i would expect something that walked like a gorilla, then had an extra smaller set of limbs for manipulating things delicately.
but it would have to exist in an environment where it was vital that it be able to both hold a thing and manipulate it at the same time. for example, some 6 legged mammal analogue that fought off predators with its central legs while holding with its front ones.
Easy. Speed. Four-legged animals run much faster than two-legged ones, and legs designed for sprinting don't make for good manipulators.

[thubby]

Easy. Speed. Four-legged animals run much faster than two-legged ones, and legs designed for sprinting don't make for good manipulators.

if it were a case of sprinting i would expect a 4 legged creature with 2 arms. either a centaur or the like

[Avilan the Grey]

Easy. Speed. Four-legged animals run much faster than two-legged ones, and legs designed for sprinting don't make for good manipulators.

...Well it is entirely situational. In general a four-legged animal gallopping is faster than a two-legged animal "galloping" but a two-legged animal tend to accellerate quicker. Also these kind of things are incredibly individual from species to species. Humans, for example, are masters of endurance. We do not run fast, but we can drive an antilope or deer to death just by jogging after it for hours and hours.

It all boils down to environment and prey. And even more importantly, what already is to work with. If, hypothetically, the fish that eventually evolved into amphibians had six instead of four fins, we might have had four arms, and all mamals, reptiles and amphibians might have had a six-limbed template. Might. Because it is also easier for evolution, it seems, to remove a limb that is not usefull than to create a new one.

Basically, a mutation that is beneficial has a high probability to become part of the genetical make up of a species.

A mutation that is pointless, such as sometimes be blonde, or have green eyes, is a "meh" from nature's point of view (so to speak). It doesn't matter, so it occurs.

A mutation that is harmful, or a mutation that is an annoyance more than a benefit? Has a high posibility to be removed from the genetical make up.

So for example, if a species have an apendage that is not used, but is not in the way and do not cost energy to have? It will probably still be there for a loong time. However if energy can be saved by not developing it as much? Or if it is in the way? Then it will be removed. Snakes is an extreme example. Whales and dolphins as well. Sealions and seals are interesting because they are a good case of parallell evolution, where one species is slightly ahead of the other (seals have been in the ocean longer than sealions, and have completely lost the outer ears and can no longer use the stubs of back legs to walk on; sealions still have very small outer ears and can support their weight on all four limbs, therefore walking instead of rutting along on the beach).

[Korgor]

On the previously mentioned spider - thing, the more usual suggestions I see are a ratio of legs to arms as 6 to 2 rather than 4 to 4, an example being the Warcraft III Crypt Fiend. Majority of your very large fantasy spiders, at least in more recent works, seem to use the front two legs as arms to attack with, but just a thought!

[WarKitty]

On the previously mentioned spider - thing, the more usual suggestions I see are a ratio of legs to arms as 6 to 2 rather than 4 to 4, an example being the Warcraft III Crypt Fiend. Majority of your very large fantasy spiders, at least in more recent works, seem to use the front two legs as arms to attack with, but just a thought!

I could see this being most likely in an environment where stability or 3-dimensional climbing are most valued. 6 legs, especially with most of the weight concentrated in the abdomen, would produce a fairly stable creature with the ability to stay on walls. Especially since spiders already do some manipulation with the front legs.

[Kelb_Panthera]

What is a 'reasonable time span'? A thousand years? How about ten thousand? Given that crossing the distance between stars could in itself take hundreds if not thousands of years with plausible technology, I am assuming any extrasolar modders would be used to playing with long, long times.
Moreover, plausible, if non existent, technologies like artificial wombs could also help speed the process, as, unlike the purely biological variety, they wouldn't reject creatures that are too different from the base creature.

Evolutionary time-scales are better measured in generations than solar-orbits. A species that cyles a generation once every ten years or so will evolve at a faster pace than one that cycles every 20 years, all other factors being the same.

[warty goblin]

Evolutionary time-scales are better measured in generations than solar-orbits. A species that cyles a generation once every ten years or so will evolve at a faster pace than one that cycles every 20 years, all other factors being the same.

Presumably if you're directly inserting and deleting genes instead of simply breeding, the process is a bit faster. It's still gonna be really slow though; particularly for larger, more complex creatures that may have fatal problems that don't express until years into their lifespan.

[noparlpf]

I might be wrong, but don't chickens' knees bend "backwards"? Or is that a misconception? I don't know chicken anatomy.

[Piet Heyn]

Walking on your toes for extended periods of time isn't at all hard for humans with some practice. For this reason, I don't see why it would be impossible for a bipedal species to naturally do so.

There's some advantages to it. As a runner, I've found that I can run faster on my toes, since there is a more spring-like aspect to my gait. The toes hit the ground, my heels move down to absorb the shock and when it's time to move that foot again the foot can move outwards like a spring once more.

[noparlpf]

Walking on your toes for extended periods of time isn't at all hard for humans with some practice. For this reason, I don't see why it would be impossible for a bipedal species to naturally do so.

There's some advantages to it. As a runner, I've found that I can run faster on my toes, since there is a more spring-like aspect to my gait. The toes hit the ground, my heels move down to absorb the shock and when it's time to move that foot again the foot can move outwards like a spring once more.

True, but walking on one's toes for extended periods (think years) is very bad for one's feet and legs. Source: My little sister is in physical therapy because she's managed to deform the skeletal and muscular structure of her feet and calves by walking tip-toe her whole life (despite all my mother's efforts to make her walk normally). Our legs aren't designed to walk tip-toe for extended periods.

[warty goblin]

I might be wrong, but don't chickens' knees bend "backwards"? Or is that a misconception? I don't know chicken anatomy.

What you see as a chicken's knee is actually it's ankle. The knee is very close to the body, and more or less invisible when the chicken's alive, since it's covered by feathers. The chicken is actually walking on its toes, unlike humans who put all of their foot bones flat on the ground. Here's a nice labeled picture (http://windward.hawaii.edu/People/Brian_Richardson/Chickens/images/Chicken_Anatomy_Large.jpg) of a chicken skeleton.

I believe this is the general leg anatomy of most birds. It shows up better on something like an ostrich, which has mostly naked thighs. Here's a video of ostriches running (http://www.youtube.com/watch?v=1r-b8uY7C9E), which also serves as evidence that the universe has a goofy sense of humor.



Walking on your toes for extended periods of time isn't at all hard for humans with some practice. For this reason, I don't see why it would be impossible for a bipedal species to naturally do so.

Walking barefoot, I find my natural stride is to land on the balls and toes of my feet, then roll through onto the heel as the stride progresses. A lot of this is I think an instinctive way to protect the foot from injury, since it avoids putting full weight on it until after I have time to detect any thorns, sticks or other spiky things that could poke me full of nasty little holes. But most of the weight is carried by the rest of the foot for the most part.


There's some advantages to it. As a runner, I've found that I can run faster on my toes, since there is a more spring-like aspect to my gait. The toes hit the ground, my heels move down to absorb the shock and when it's time to move that foot again the foot can move outwards like a spring once more.
I believe this is currently believed to be how people naturally run, and the heel-first gait is an artifact of wearing stupidly built up padded shoes.

[Piet Heyn]

True, but walking on one's toes for extended periods (think years) is very bad for one's feet and legs. Source: My little sister is in physical therapy because she's managed to deform the skeletal and muscular structure of her feet and calves by walking tip-toe her whole life (despite all my mother's efforts to make her walk normally). Our legs aren't designed to walk tip-toe for extended periods.

But another species, one that naturally walks on their toes, probably would not have that issue. Which is why it's entirely feasible.

[noparlpf]

What you see as a chicken's knee is actually it's ankle. The knee is very close to the body, and more or less invisible when the chicken's alive, since it's covered by feathers. The chicken is actually walking on its toes, unlike humans who put all of their foot bones flat on the ground. Here's a nice labeled picture (http://windward.hawaii.edu/People/Brian_Richardson/Chickens/images/Chicken_Anatomy_Large.jpg) of a chicken skeleton.

I believe this is the general leg anatomy of most birds. It shows up better on something like an ostrich, which has mostly naked thighs. Here's a video of ostriches running (http://www.youtube.com/watch?v=1r-b8uY7C9E), which also serves as evidence that the universe has a goofy sense of humor.

Ooh, neat. I'm saving that picture. Thanks!

[Avilan the Grey]

As a sidenote:

Did anyone laugh at the Tali / Garrus discussion about human and asari legs during the Citadel party? They both find our legs looking freaky and can't figure out how we don't fall flat on our noses when we try to walk...