First: I know that things occur in cartoons that are impossible in the physical world. (Squashed coyotes do not walk away making an accordion sound.) Nevertheless, this question is based on something I saw in a cartoon.
In the cartoon was an extraterrestrial civilization. They were basically humanoid in form (as are the denizens of most fictional extraterrestrial civilizations), but with one striking difference: their bipedalism was the reverse of ours. From their shoulders, their forelimbs reached the floor and had feet on the ends. From their hips, their hindlimbs were held off the floor and had hands on the ends.
I wonder if this is evolutionarily plausible. Here on earth, when I look at bipeds unrelated to us â bipedal dinosaurs, including todayâs birds â they did it the same way we did, that is, retaining the hindlimbs for walking and modifying the forelimbs for other purposes. Still, there are other animals â whales, sirenians, and sirenidae â which lost the hindlimbs entirely and retained only the forelimbs; although in all of these cases, it occurred in an aquatic context and cannot really be called bipedalism in the terrestrial sense.
So, how 'bout it? Is a terrestrial animal, bipedal on its forelimbs, evolutionarily plausible? If so, how might this come about?
I donât think so, as it seems to be a physically pretty instabile solution. I think it would be more likely for those whales to reuse those genes for hind limbs that are dormant somewhere⌠Or just die off, if walking would be necessity againâŚ
First of all, of course coyotes make accordion sounds when their spines get compressed. You mustâve watched the same documentary I did when I was six.
Secondly, that sort of design would be implausible and inefficient. Our legs are positioned the way they are, directly underneath our center of gravity, specifically to support our weight and aid with balance. Having our legs from our shoulders would put massive strain on the bones and joints, and would cause our âarmsâ and bodies underneath them to sway precariously like one of those swinging pirate ships, causing balance issues and more strain. I could only see this design being biologically efficient if the environment was low-gravity, if the speciesâ heads were massive to counteract the weight below, and the torso and âarmsâ were severely reduced. Otherwise, I think natural selection would wipe that species out within a few generations.
Well, speculatively speaking, I could see it. Basically, it seems like this would involve swapping the positions of the head and genitals. Such evolution would require change the pelvic structure and shoulder structure, of course. But, I could imagine there are circumstances where such a configuration might work.
There are - even in quadrupeds - quite a difference in anatomy between front and rear limbs. Power of movement and flexibility is in the rear, so it makes perfect sense that a meerkat stands up on its hind legs to see around and doesnât do handstands (that plus - heads are at the top! You would need some major changes to move that because it starts from early on in the embryo - including gradients that âcodeâ top from bottom telling everything where to go - and all this would need flipped at almost every development stage!). Even in dog training we often warn people away from teaching handstand tricks because most dogs, their structure, this puts severe strain on, asking them to move beyond safe motion and even if a dog is willing to comply that doesnât mean it is safe; but they like meerkats can easily sit up on their hind.
If anything, human bipedal posture can hold safely a handstand position better than any quadruped; there are plenty of examples of double amputees who walk on their hands. But i doubt this catches on as again, it puts the head in a more precarious place. This said - despite being totally not likely to happen - i think a reverse bipedal posture would be more likely (but not at all plausible) to develop from humans than any other critter. I would also question how different it would look once evolved, from how we are already.
I think one could imagine a gravity, atmosphere, and environment setup on a planet somewhere where a life form like that could exist. Imagine low gravity and abundant tree branches to grab onto, a thick atmosphere, etc. The strong rear arms could be used to affix sideways to tree limbs and the smaller forearms used for reverse bipedalism but only in limited settings as the species spent more time in the trees. That being said, as an in-universe answer, given it is star wars, the species may have been genetically engineered to be able to fit into and quickly drive those pod races or other spaceships, rather than having evolved naturally. Star Wars is definitely not hard science fiction but borrows from such. :) And the article says their natural environment is âdeserts and wastelandsâ and that does not strike me as a good body form for a desert species, unless there were lots of rocks to climb on in canyons or something.
It is both possible and plausible, depending upon the meanderings of evolution.
Macroevolution is an absurdly unpredictable process. Who among us, seeing an early lobe-finned fish, would have thought it could evolve into a hummingbird? Who, seeing early snail-like molluscs could have predicted flying squid? Etc.
There is a wonderful old and widely praised speculative zoology book called âAfter Man.â In a world where humans have long since gone extinct and taken most animal diversity down with us, there is a group of animals, called Night Stalkers, that have evolved from bats, they walk on forelimbs modified from bat wings and grab with the hindlimbs. In the absence of other land mammals, when the hind-limbs are specialized for some non- locomotor function, why not use the forelimbs for getting around?
Function aside, any trait can be selected for if it is found to be âattractiveâ and increase the chances of reproduction. You just need to find a species that digs the anti-Tyrannosaurus look
The question reminds me of the book (somewhere in my library) âThe Snouters: Form and Life of the Rhinogrades.â Surely if we humans can imagine a vertebrate lineage that involves incredible adaptations of the nose for various life styles, evolution could probably come up with a reversed bipedal creature. Whether it would be adaptive for a vertebrate to go down that path is another question.
this triggered some fun imagery in my head. i can imagine a quadruped animal wanting to go biped occasionally (or pseudotriped with the aid of a tail) to get its mouth closer to food. but maybe there would be some case where it would be beneficial to get your genitals or butt closer to some object of desire? imagine the beginnings of that kind of evolutionâŚ
Skipping the vagaries of plausible and possible and going to a scale of 1 to 10 I would give it a 0.5 assuming the original creature was a quadruped. Even if we assume an intermediary form like a bird it seems extremely inefficient to start using the back limbs for grasping and the forelimbs for locomotion. Penguins and ostriches lost their ability to fly yet in neither case was it more effective to use ancient forelimbs to move and rear limbs to grasp. Both use head/beak. Grasping happens at the front. Running happens at the rear.
Fascinating question, Jason! I just finished rereading âLucyâ by Donald Johanson and Maitland Edey. The authors go into excruciating detail about how bipedalism might have arisen in hominids in the first place, with some really good evolutionary context by Prof. Owen Lovejoy in Part Four of that book. Your question might be turned into a type of âmind puzzleâ not unlike those that Albert Einstein would entertain. So, theoretically, what evolutionary pressures (of environment, resource competition, etc., etc.) might result in giving incipient re-bipedalists a slight reproductive advantage?!
Maybe in an arboreal species, like orangutans⌠that stays arboreal. Or, see bats, they donât appear to have developed hind limbs, except that they perch with them, so they are used for grasping
Like others have said: In the context of our current evolutionary reality, the only organisms today that come close to your description are a select few sequipedal arthropods such as Crabs, whose front set of claws might be lower set below the plane of leg attachment in a select few species. Reason being is likely that all land-based organisms have evolved to have stability of movement and a low centre of gravity, as others have said. Reverse bipedalism just didnât provide this along the evolutionary path that life on earth followed. Had evolutionary pressures been different in the early stages of our planet however, Iâm sure this couldâve been a possibility
Do they grasp things with their hind legs while walking on their wings? Or is it just that their primary means of locomotion is their wings and their legs are largely useless?
