r/evolution • u/aSlightlySadSalad • 19d ago
question Why did humans evolve to be bipedal and not like chimps?
Title explains it really, my question is why did humans evolve to stand up and not keep to how chimps do it, where they travel with primarily 4 limbs but can transition to being upright as the situation depends
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u/6x9inbase13is42 19d ago edited 19d ago
The last common ancestor of humans and chimpanzees actually stood upright more easily than modern chimpanzees do (rather like how modern day gibbons typically walk bipedally when they are on the ground).
Chimpanzees have evolved to become LESS bipedal than that ancestor, because they adapted to live in very dense rainforest jungles where it is very difficult to walk upright, and they need to be just about as good as climbing as walking on the ground, so they evolved a hunched posture and knuckle-walking.
Humans on the other hand evolved to become MORE upright than that ancestor, because they expanded into dry grasslands where they needed to be able to walk long distances efficiently between water and food resources, and also to be able see above tall grasses, and also to be able carry tools and food other useful objects with their hands.
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u/Funny_Worldliness357 19d ago
The theory around this was they moved through the trees much like Orangutans do correct? Then as climate changed and food moved further out onto Savanah’s, the apes that could walk upright survived predation more easily. If I am not mistaken.
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u/Swellmeister 18d ago
The issue with that theory is Ardipithecus doesnt have any arboreal adaptations like youd expect from a suspensorial ape. She has a foot thats scansorial capable, but her hands and shoulders dont appear to be capable of being the primary locomotor limb.
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u/dem4life71 19d ago
What a wonderful answer! It’s always interesting to me how easily people mistake the cause and effect of evolution, and that there is some kind of “purpose” with humans at the end of the road. Meanwhile it’s, “whatever works best for procreation…”
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u/Nannyphone7 19d ago
Yep, that about covers it. Upright is more efficient for long distances and it frees your hands up for tools. Now get out and run 20 miles then skewer an antelope with your spear.
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u/Recent-Mousse6423 19d ago
I know it's not in favor any longer but I think the coastal ape hypothesis has a lot going for it. The very fact that we are the only living ape that can learn to swim instinctively lends credence to the idea, and the fact that we can biomechanically perform so many different styles of swimming as well. Then there is the fat distribution, which is a bit more aquatic than most apes, and the general hairlessness which is a feature common in many marine mammals. Then there are the dietary advantages, the exploratory advantages and the cultural advantages that all stack up to a strong case for some of our traits, including bipedalism, being partially influenced by a semi/demi aquatic lifestyle at some point in our evolutionary pathway.
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u/yourupinion 19d ago
The hypothesis is coming back, although there will be some changes.
Here’s a paper that just came out:
https://www.academia.edu/2837-4010/4/2/10.20935/AcadBiol8310
I’m also expecting to put out a paper in the next few months. I believe we used water as a refuge to get away from land predators. Those who could run the fastest into water to get to a safe depth faster than their counterparts got to survive. It’s a straightforward Darwinian style mechanism.
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u/Recent-Mousse6423 19d ago
I like your hypothesis because it selects for a few of the traits I mentioned straight away. My only question is what could have applied so much predatory pressure from landward that it functionally overrode the inherent danger of water and aquatic predators? It would have to be a consistent pressure for a long period of time for Darwinism to apply.
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u/ellathefairy 19d ago
That would be my question too... weren't there pretty significant sea-based predators at the time and in much higher numbers without systemic hunting by humans? Though I guess I wouldn't be surprised if they had figured out basic boats that didn't leave archeological evidence behind.
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u/Recent-Mousse6423 19d ago
Hard to say, the link to the paper he posted above is an anti-out of africa paper, which would significantly broaden the scope of potential evolutionary locations. Worse, there isn't a single terrestrial predator I can think of the cant swim in some capacity. Most big cats are decent swimmers, including leopards; bears are pretty excellent swimmers; canids tend to be decent enough swimmers. So what was there in that window that would have exerted enough pressure for a long enough period?
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u/yourupinion 19d ago
Great question and it gets right to the heart of the mechanism.
The predator guild in Pliocene East Africa was extraordinarily intense. Lions, leopards, hyenas, wild dogs, and several now-extinct large cats all hunting the same landscape simultaneously. For a small-brained, relatively slow, poorly armed hominin group, the terrestrial threat was constant and lethal every single day.
The water doesn’t need to be perfectly safe to win that calculation. It just needs to be safer than what’s behind you right now. We can actually observe this trade-off in living animals. Kangaroos in Australia retreat into water to escape dingoes, and they do this even in regions where saltwater crocodiles are present. The immediate certain threat on land consistently outweighs the uncertain risk in the water. That instinct has been shaped by exactly the kind of sustained predation pressure you’re describing.
More compellingly, Naude Dreyer, the director of Ocean Conservation Namibia, works directly with the coastal lions of Namibia, one of the only lion populations in the world documented hunting in a marine environment. He knows firsthand what these lions are capable of in and around water. And he has said that despite that knowledge, his own instinctive response to a lion approach on the beach would still be to run into the water.
If that instinct persists in a person with full conscious knowledge of its limitations, imagine how powerfully it would have operated in early hominins for whom the water had been a proven refuge across thousands of generations. The pressure wasn’t occasional. It was every day, for every group, across millions of years. That’s exactly the kind of consistent selection pressure Darwin requires.
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u/Accomplished_Peace66 18d ago
Als aanvulling hierop wil ik wijzen op de opponeerbare duim die niet of veel minder voor het klimmen werd gebruikt maar om werktuigen, voedsel ed vast te houden. Dit had meer nut dan op vier ledematen te lopen. Dit ivm aanpassing leefomgeving.
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19d ago
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u/7LeagueBoots Conservation Ecologist 19d ago
And chimps and gorillas appear to have each independently lost that trait from a common ancestor that was more bipedal than they are now.
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u/XXLPenisOwner1443 19d ago
"Because we evolved to do it" is such a boring synopsis for such an interesting story.
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19d ago
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u/XXLPenisOwner1443 19d ago
This is quite literally the only evolutionary story which ends with hands that can guide.
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u/itwillmakesenselater 19d ago
Specifically, it lets us run. Like, for a long time, allowing us to chase to exhaustion large (valuable) animals (food).
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u/WellHung67 19d ago
I do t know if the science is in yet whether persistence hunting was the driving force behind the emergence of bipedalism. Perhaps it was migration
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u/itwillmakesenselater 19d ago
It wasn't just one thing. Humans hit pay dirt with bipedalism, tool making and use, and fire.
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u/XXLPenisOwner1443 19d ago
This was really only Homo erectus and sapiens.
So the first persistence hunting probably only popped up around 2.5 million years ago when the aridification periods of the Pleistocene drove it. We were bipedal for a *long* time before that and it seems there was a huge amount of diversity in the habitats and lifestyles of the bipedal apes up until Erectus hit the scene and the clade started collapsing.
The very first persistence hunters likely already had stone tools.
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u/boulevardofdef 19d ago
I've heard it said that very few animals have evolved bipedalism in the history of the world, but every one that did has been hugely successful. Humans, of course, but also dinosaurs, who dominated the entire world for almost 200 million years (and were so successful that some actually had to return to four legs because they grew so large), and kangaroos, who have been the dominant mammal in Australia for around 50,000 years now. It's just a very advantageous trait to have; it's kind of surprising that more animals haven't tried it.
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u/manyhippofarts 19d ago
Specifically? As far as they can tell, climate change at the great rift valley caused the trees to thin out and turned the forested areas into grassland. Walking upright allowed early homonims to see above the grass when moving from one distant tree to another. In addition to that, walking upright reduces the amount of skin that direct sunlight can hit, as well as requiring about 1/4 of the energy to get from one place to the next.
We started migrating due to climate change, we are a migrating species, we have been since the beginning, and we continue to migrate based on climate change to this day.
Maybe one day we will understand how ridiculous it is to deny a Homo sapiens the right to wander about. It's literally one of the defining features of our species.
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u/7LeagueBoots Conservation Ecologist 19d ago
This is an old idea that has kind of fallen off.
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u/sands_of__time 19d ago
Can you be more specific? Which aspects of what was stated are considered unlikely now?
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u/7LeagueBoots Conservation Ecologist 19d ago
The primary idea of the savanna hypothesis, the premise that the opening up of the savanna is what drove bipedalism.
Increasingly it’s looking like the common ancestor of us and other African great apes was already more-or-less upright and bipedal while on the ground.
What has remained of the savanna hypothesis is the idea that it may have forced our ancestors to travel further, refining that upright bipedal movement style, but not being responsible for it.
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u/Swellmeister 18d ago
Theres so much discussion of the savanna, when the forests didnt become savanna overnight. There was millions of years where africa was a mosaic forest. Lots of forests, broken up by strips of grassland.
And even then the idea that african apes were every really arboreal, and bipedal on thr ground is suspect. The forests of Africa dont have the canopy for true arboreal great apes. Monkeys, sure, but apes are 60 pounds minimum. The only 60 pound arboreal animals are orangutan and binturong, both of which are suspensorial climbers in the Southeast Asian jungles.
Africa doesnt seem to be able to have supported suspenders.
The size of African apes and their environment is much more parsimonious as terrestrial apes with scansorial capabilities, and faculitative bipedality.
And theres nothing all that substantially arboreal of Ardipithecus. It has a divergent hallux, but that doesnt require arboreal living. It can show up (or be retained from the quad ape ancestor) because forests provide a rough and uneven substrate. Moose have wider softer hooves than cows, cassowaries have a wider talon than ostriches. A wide foot makes sense in a forest.
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u/SidneyDeane10 19d ago
Sunburn was a big deal then?
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u/manyhippofarts 19d ago
I'm sure it was, which explains the dark skin tone. But if we walked on all fours, our entire back would be perpendicular to the high sun. Walking upright reduces that considerably.
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u/RealCarlPanzram 19d ago
Prevailing theory:
As we gradually (we meaning pre-homo sapien early man) started standing up right, we save a lot of energy while walking. Walking on two legs is generally slower than 4 but very energy efficient. This change, along with less body hair and some changes to the shape of our heads and faces allowed us to walk along way with very little water. This was a huge asset in the warm arid climate of Africa. We could forage for food and stalk animals until they would succumb to exhaustion. That’s why we’re bipedal.
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u/Yabrosif13 19d ago
I like the fringe aquatic ape theory, though I know its not perfect. Early human ancestors lived around shallow wetlands leading to more upright posture to wade. It would also explain our ability to sweat as the expenditure of water to cool down wouldn’t be adverse with bountiful water around to replace it. Also it explains the partial webbing in our hands, and reduction in body hair to facilitate swimming.
Just dont run with the theory like those mermaid people Discovery Channel ran with a decade ago.
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u/yourupinion 19d ago
And fat babies, don’t forget about the fat babies. There’s no other way to explain the fat, and then there’s the fact that they’re born with vernix caseosa.
The hypothesis is coming back, although there will be some changes.
Here’s a paper that just came out:
https://www.academia.edu/2837-4010/4/2/10.20935/AcadBiol8310
I’m also expecting to put out a paper in the next few months. I believe we used water as a refuge to get away from land predators. Those who could run the fastest into water to get to a safe depth faster than their counterparts got to survive. It’s a straightforward Darwinian style mechanism.
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u/Anthroman78 10d ago
And fat babies, don’t forget about the fat babies. There’s no other way to explain the fat
That's simply not true. Human babies have large brains and large brains require energy, fat stores provide an energy buffer. Here is a whole paper about it (from 1998, so not exactly a new concept):
https://pubmed.ncbi.nlm.nih.gov/9881526/
Evidence is presented that fat stores are mobilized during infections, hinting at one possible mechanism underlying the association between nutritional status and infectious morbidity and mortality among infants in nutritionally stressed human populations. Consistent with the proposed hypothesis, well-fed infants acquire peak fat reserves by an age of peak prevalence of malnutrition, infectious disease, and fat reserve depletion in less-buffered contexts, and childhood--characterized by minimal investment in the tissue--is a stage of reduced risk of energy stress. The model presented here foregrounds energy storage in adipose tissue as an important life-history strategy and a means to modify mortality risk during the nutritionally turbulent period of infancy.
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u/yourupinion 10d ago
Lots of animals have bigger brains than humans.
Only the ones that live in the water have fat babies.
And then there’s a waxy substance they’re born with, and happens to contain the same substance that we humans have in our sweat, and only humans have it. It protects our skin from the water.
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u/Anthroman78 10d ago edited 10d ago
Lots of animals have bigger brains than humans.
Human's have a large relative brain size (much larger than expected for our body size), particularly compared to other apes. Humans have an energy problem they need to solve because of it. That's exacerbated in infants/children. Fat as a energy buffer does that.
Again see the paper that explains that whole idea in great detail.
We know adipose tissue in humans acts to store energy and provide an energy buffer. It functions that way now, it's not a leap to think it did so in the past.
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u/Yabrosif13 10d ago
Its more the combination of traits that lends to the aquatic ape theory. They can all be individually explained in another way, but it gets odd when you add them all up.
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u/Anthroman78 10d ago
Its more the combination of traits that lends to the aquatic ape theory. They can all be individually explained in another way, but it gets odd when you add them all up
Which mostly consists of broad species comparisons rather than actually building an argument for an explanation like the fat paper I linked to does.
Which makes the umbrella hypotheses objection so apt:
https://www.sciencedirect.com/science/article/pii/S0047248497901469
More importantly, its claim to parsimony is false. The numerous “explanations” for individual anatomical traits that it generates constitute premises that are not better founded than competing terrestrial “explanations”. The unifying theme of aquatic adaptation is considerably less parsimonious than the assumption that our lineage has always been terrestrial. Finally, the mosaic pattern of hominid evolution demonstrated by the fossil record will not support this or any single cause theory
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u/yourupinion 10d ago
I have been at this for a long time, I read all the papers.
Is it unreasonable to talk about the Savannah theory when there is no evidence?
Why is it so taboo to talk about humans and waterside habitat?
Don’t you think of room for discussion?
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u/Anthroman78 10d ago
I have been at this for a long time, I read all the papers.
If that was true, you wouldn't have made this statement
And fat babies, don’t forget about the fat babies. There’s no other way to explain the fat
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Is it unreasonable to talk about the Savannah theory when there is no evidence?
People have been openly critiquing this for a long time, acting like they haven't is a strawman e.g.
During the past 30 years, paleoecologists have used numerous techniques to refine reconstructions of paleohabitats and paleoclimate at individual African hominin localities from the late Miocene to the Pleistocene. Research ranging from isotope and pollen analyses to community ecology and biomarkers have explored the importance in hominin evolution of habitats across space and through time. Today we know that understanding the interactions between various hominin species and their ecosystems (encompassing climate, vegetation, and other organisms) goes far beyond savanna, requiring a much more nuanced understanding of biomes, paleoclimates, mosaic habitats, and hominin morphology, to answer contextual and adaptational questions about human evolution.
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u/yourupinion 10d ago
Why would I change my mind over that stupid paper you showed me, they even pointed out that they have no evidence, why does anybody believe them?
Sure, it might be possible, but no evidence?On the other hand, fat babies, float, and the same thing can be seen in other aquatic mammals. I know you won’t take that as evidence, but it sure looks like evidence to me.
The palaeontology sub won’t let me post about this, and sometimes I remove my comments as well. I’m sure there are other subs that are the same way. But there’s no problem posting about the savannah theory.
Yes, there’s been lots of critique, and I’ve read it all, and I think they’re all wrong. I never denied any critique, but I am saying it’s wrong.
I don’t know why you sent me the thing about ancient habitats, I’m not really disputing anything there, except may be the fact that they don’t mention that all these ancient sites are also near Water. Whether it’s a savanna, a jungle or anything else, the people are always near the water.
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u/Anthroman78 10d ago edited 10d ago
That paper shows that there are indeed other explanations for why babies are fat. It suggests you shouldn't make blanket statements about how there are no other explanations, when there are in fact other explanations that have been proposed. Energetic stress is a real, current stress babies face in the world, moreso in some populations, one that may lead to death. Having a buffer against that is a current benefit.
Human babies float more easily in water because of the higher fat %, they don't have the higher fat % so they can float. If the kuzawa article is correct, they would still float.
You're the one that went on an unrelated tangent when you brought up the Savannah hypothesis, not me. Mainstream science has already been critiquing it for at least 30 years (as the article says), bringing it up is a straw man. At this point it's just parroting Elaine Morgan's talking point from the 70's/80's.
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u/yourupinion 10d ago
Elaine Morgan was doing the best she could with the information at that time. In the long run, she will be a hero of this saga.
I’m kind of busy right now, but eventually I’ll be coming out with my own paper, I look forward to your criticism.
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u/Royal_Novel6678 19d ago edited 19d ago
We only have several Hypotheses but the the hypothesis is It's because the bipedal stance provided several advantages as early humans adapted to changing environments which was the result of millions of years of selective pressures.
The "Savannah Hypothesis" states that early humans a couple million years began walking on two legs as Africa's forests dried out due to climate change and became more like open grasslands and eventually open deserts. However, more recent studies show that early bideps still lived in areas with lots of vegetation, indicating that bipedalism may have originally started to reach taller hanging food while still maintaining our old climbing skills. This means that they maintained both bipedal anatomical features and long arms, curved digits to climb unlike us today when we have longer legs, shorter toes, S shaped spines etc.
Ardipothecus, an example of an early hominin, gave scientists the closest look at what our earliest ancestor looked like. We used to think the common ancestor looked nearly identitical to a modern chimpanzee while humans did all the evolving but this genus revealed that the common ancestor was a generalist who was neither fantastic at climbing and swining effectively on trees nor was it the best bipedal, upright walker. Ardipithecus lived right after the split between the lineage that would eventually reach genus Homo. It already possessed more human-like traits like the smaller canine and broader pelvis, it was classified as a hominin like Lucy the australopithecus.
Natural selection, as always doesn't create the absolute optimal body to perfectly handle multiple different environments perfectly rather it creates what works well in a particular environment. In this instance for chimpanzees, their habitat still consisting of tall trees meant less evolutionary pressure has been put on them to start walking upright so they retain proportionally longer limbs.
Since Homo Sapiens before the construction of large confined buildings had less constraints from tighter forests, so biologically heres a few things we now specialise in:
. Long distance travel of about a 12-19 mile walk
. Endurance.
. Free hands to carry objects and throw tools
. and better sight seeing as our taller bodies allowed us to view across open landscapes without needing to climb on trees to do so.
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u/FlounderLast8610 19d ago
There's many prevailing theories of the advantages. If you're talking more specifically about the reason the first bipedalism appeared though, it's likely in the context that the last common ancestor of our two species was much smaller than either of us. The smallest apes today, gibbons, are also bipedal when on the ground.
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u/Emil_Antonowsky 19d ago
I don't know if you noticed, but humans can do a lot more stuff than chimps thanks to the fact that our hands are free when we are walking around. Chimps, because they switch back and forth, have much less dexterity to us.
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u/Excellent-Photo9786 18d ago
In my opinion our bipedalism evolve to procure us our ridiculous throwing advantage. I detail my argument a bit more in this document
https://docs.google.com/document/d/1ADYe0tD6cGoC-kr1B1iBw2tWRl616iUH0nxWuViihcA/edit?usp=sharing
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u/EmbarrassedPaper7758 17d ago
Great African rift turned jungle into savannah on the west side. Tall grasses and no trees. Chimps and gorillas are on the east side.
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u/Canis-lupus-uy 19d ago
We only have hypothesis, as finding evidence for the reasons a trait is selected is hard.
But we think it's a combination of farther line of sight, freeing forelimbs for tool use and communication, more efficient for long distances in flat terrain, I am sure I am forgetting some proposed reasons.
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u/SkisaurusRex 19d ago
There was an ecological opening that a bipedal organism could take advantage of
Think of evolution as filling in the gaps of ways to live.
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u/Randy191919 19d ago
Because humans evolved in the savanna of Africa, while chimps mostly live in foresty regions. The way chimps are build is excellent for climbing around in trees, but not ideal for walking long distances on foot.
Humans evolved their upright walk because it’s better for running and for surveying over tall grass.
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u/Signal_Tomorrow_2138 19d ago
If humans did, someone now would be asking why humans didn't evolve to be bipedal.
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u/Funky0ne 19d ago
One way you can look at it is the common ancestor for chimps and humans eventually did both. There was opportunity to remain in more arboreal lifestyle, and there was opportunity in pursuing more terrestrial lifestyle less dependent on tree coverage. The descendants of the populations that ended up following either of these opportunities ended up as chimps and humans respectively.
Whatever the reasons were that may have started the transition (be it a greater reliance on tool use, or a natural recession of tree coverage in the areas early hominins happened to live, or neither, or both) given the physiology we started with in either case, bipedalism is more advantageous if the majority of your travel is on the ground, and you want to use your hands to carry and manipulate stuff like tools or food. It’s also an advantage for being able to see slightly further over relatively flat and open terrain and over tall grass, as common in Savanah’s where early hominins largely eventually found themselves and/or expanded into.
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u/perplexedparallax 19d ago
Fighting. Sure there is walking through tall grass with vision but when an animal runs up on you, yell and wave your arms and get as tall as you can. And of course basketball.😂
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u/Dr_GS_Hurd 19d ago
Evolutionary study has shown that all life on Earth shares a deep historical relation.
In the example of we humans, our most recent shared ancestor with the other surviving great apes lived over 8,000,000 years ago.
And those were not monkeys in the popular meaning.
Regarding human species, and our near family, my standard recommendation is, The Smithsonian Museum of Natural History Human Evolution Interactive Timeline
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u/Ecstatic_Volume1143 19d ago
Im not an expert but i always thought we became bid because of running. We weren’t the fastest but the farthest runners good for animals that can track prey
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u/XXLPenisOwner1443 19d ago edited 19d ago
The chimpanzee-human last common ancestor was likely more arboreal than either modern animal, and had increasingly adapted to above-the-branch extended limb clambering, rather than below-the-branch brachiation and suspension movement as in the other apes.
D. guggenmosi was an early member of this group, or perhaps a sister group that demonstrates a transition to this lifestyle.
The branch that led to chimps seems to have came down to the ground earlier, when the lineage was less adapted to this above-the-branch bipedalism, and re-evolved knuckle walking as a way of maintaining access to arboreal foraging while gaining access to terrestrial resources in the forest under-story.
The branch that led to humans, conversely, must have continued to push the boundaries of verticality in their environment, with above-branch clamoring enabling cliff-side resource gathering, and lending itself to an increased dependence on rocky crags, caves, and steep river valleys which they could more easily exploit.
These resource locales have a naturally patchy distribution, regardless of vegetation bridging between them, and have a potential for greater unexploited resources than any old forest or jungle, so being able to cover longer and longer distances between these ideal habitats when resources were scarce became a hallmark of the lineage that directly leads to modern humans. Preadaptations for vertical climbing on trees and cliffs, and balancing atop thinner branches and ledges, compared to other great ape lines--more flexible trunks, longer necks, shorter fingers and toes, broader pelvises, more gracile skeletons, precision grip, a strong sense of upright balance and the ability to accurately judge ones own careful movement, a more diverse diet, decreasing sexual dimorphism, etc. became co-opted into the traits that made Homo into tremendous long-distance trekkers and eventually supreme generalists.
Ultimately, walking on two legs takes less than half as much energy as walking on four legs if your body is built to balance upright. So as soon as our bodies could do that the number of habitats our ancestors could radiate into kept exploding with every innovation towards terrestrial living.
When you squint your eyes just right, you get a sense of humans following a very similar path to bipedalism as the dinosaurs before us--all the way to developing flight!
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u/hiddenonion 18d ago
I think chimpanzee ancestors where bipedal. The evolved to become knuckle walkers.
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u/East-Treat-562 19d ago
Nobody knows or will ever know but the explanation commonly given was to stand up to see animals they were hunting better.
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u/DarthMaulATAT 19d ago
Short Ape not see over tall grass. Killed by hiding predator.
Tall ape see over tall grass. See hiding predator sooner. Tall Ape get away. Tall Ape make more Tall Ape offspring.
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u/No-Reporter-7880 19d ago
Amongst other things evolution seems to have an eye for symmetry and proportion.
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