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Why did humans straighten up?

force_redo

Thinker
F
Joined
Jul 28, 2005
Messages
146
I guess I'm once again missing out the correct terminology here, but what I mean is:
At some point we started walking upright as opposed to "on all fours", despite the loss of speed and despite the fact that it's apparently more economical to walk on all fours

I heard two theories a while ago:
1.) Because we needed the hands free for the use of tools.
2.) There was some shortage of supplies (food) so supplies needed to be carried longer ways / more at once.

Whilst I find 2.) more beleivable, since primates use their hands, too and still occasionally walk on all fours, I'd love to know what the current state of this debate is.

Thanks a lot,
FR
 
God designed us that way silly.

Seriously, there is no "why" in evolutionary development, it just happens the way it happens. Natural selection tells us that developing the ability to walk upright either helped our ancestors to survive or, at least, did not hinder their survival.

If I were to make a wild guess at rationalizing it, I would say it was because as the hand specialized as a tool using appendage it became less suitable for use in walking.
 
The short answer is that it had much to do with man's ancestors finding themselves on the wrong side of the great rift in Africa which put them in a grassy steppe instead of in a forested or bushy region. Knuckle-walking through 4' or 5' tall grass is not a great idea because you can't see predators that might be lurking nearby and that could probably hear you shuffling through the grass. Learning to stand up to look over the grass gave you a distinct advantage over those who didn't.
 
Psi Baba said:
The short answer is that it had much to do with man's ancestors finding themselves on the wrong side of the great rift in Africa which put them in a grassy steppe instead of in a forested or bushy region. Knuckle-walking through 4' or 5' tall grass is not a great idea because you can't see predators that might be lurking nearby and that could probably hear you shuffling through the grass. Learning to stand up to look over the grass gave you a distinct advantage over those who didn't.
Click to expand...

Aha! Thanks a lot. I haven't heard that one yet. Is this the current "state of the art" explaination? Or is there still a debate going on?
(I don't mean the "usual" sort of debate that is always going on, more like the "you are ignorant" - "no you are ignorant" sort of debate)

Because from my naive point of view I would argue that a monkey's or meerkat's approach would do the trick, too. As in: Stand upright to spot the predator and then use the advantage of speed on all fours to get away from it. But, I'm really not arguing, I don't know anyting about it, I just want to learn.

ETA: Or what about growing a long neck and stay on all fours?
(Yes, I'm perfectly clear that "choices" of evolution are by no means "decided" by somebody. I'm just curious why one approach prove to be fitter than another. I just use this baby-language, since my english is a bit limited)

FR
 
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I'm currently reading Taking Darwin Seriously my Michael Ruse. Along the lines of what Psi Baba wrote, he says it was because of changing climate (drought) in Africa that changed the environment from forest/jungle to grasslands.
 
It should be added that true bipedal locomotion is a very efficent way of covering long distances (although perhaps not quickly). Efficiency of motion allowed our ancestors to travel farther while searching for food/water/shelter, especially with the added benefit of having hands free to carry supplies & tools, rather than having to rely on what would be available on site. Our ancestors populated the entire world largely by foot whilst other primates have been tied to their native habitats.
 
Watch meerkats sometime, or prarie dogs, both plains-living group-living animals. The sentry position is enough to warrant some ability to stand bipedally, as when one person is sentry over a large group, it reduces the time for each spent watching for predators. A lone ostrich spends roughly 30% of its time scanning for approaching animals. An ostrich in a group, by contrast, spends less than 10%, relying on the other animals for an alert and allowing it to forage more.

If being able to stand was an advantage, the folks who could do it without much of a break would allow their fellows a better survival chance, and provide a survival advantage for the group. A sentry who has to get up and down a lot draws attention to the group, as does frequently changing sentries. Baboons rely on other prey animals for some of their warning, and most prey animals will be alert to a nearby giraffe.

In the plains, distance is the best cover you have.
 
There are lots of factors that contributed to the ability. However, in short, the reward was more energy. Walking upright saves you a few calories a year when compared to walking on all fours. Momentum helps take the next step, so when you're scavenging for food being able to trek longer distances is of advantage. I think I heard it said somewhere (Sir. Robert Winston perhaps) that you save roughly the equivalent of a packet of biscuits a year by walking upright.

Dry climates also meant that large open expanses were the mainstay of the environments of food-seeking proto-humans. Selection favoured less hair and more sweat glands to help dispense of body heat more efficiently as well; it's argued that the development of early forms of language around this time meant the mouth and tongue was more useful for communicating than heat loss, hence adapting in a different way.

Athon
 
I remember reading somewhere, years ago (I wish I still had the source) that walking upright also prevented early bipeds from soaking up too much sun (less surface area exposed), once they made the move from forests to grasslands.
 
Beady said:
I'm told that, over long distances, a human can outwalk a horse. Not sure how true this is, but it would be a good illustration of the point if you can substantiate it.
Click to expand...

There have been long-distance races between people and horses. This was the first thing I found from google, not very informative, but I know it's not the only example:
http://www.kidzworld.com/site/p1808.htm

So humans are definitely competitive with horses at long-distance running.
 
Most animals overheat very easily. Most big cats have to stop or will kill themselves through heat exhaustion, so for us I guess it would have been a further advantage against predators.

Athon
 
I thought it was because God made us that way.

No, but seriously, if I walk on all fours for more than an hour or so my back really hurts. I'll bet knuckle-walkers had sore backs.
 
Starthinker said:
I thought it was because God made us that way.

No, but seriously, if I walk on all fours for more than an hour or so my back really hurts. I'll bet knuckle-walkers had sore backs.
Click to expand...
Why do you walk on all fours for up to an hour? :eye-poppi
 
force_redo said:
Because from my naive point of view I would argue that a monkey's or meerkat's approach would do the trick, too. As in: Stand upright to spot the predator and then use the advantage of speed on all fours to get away from it. But, I'm really not arguing, I don't know anyting about it, I just want to learn.
Click to expand...

Proto-humans in a savannah environment did not have such a speed advantage, however. In addition, it's a grassy environ - they needed to stand -all the time-. Chimps can do this, but their neck, back, legs, etc. do not support it well.

ETA: Or what about growing a long neck and stay on all fours?
(Yes, I'm perfectly clear that "choices" of evolution are by no means "decided" by somebody. I'm just curious why one approach prove to be fitter than another. I just use this baby-language, since my english is a bit limited)

FR
Click to expand...

IIRC our necks are longer. It's just that the 'walking upright' bit was the easier, faster transition, since our ancestors were already capable of the basic posture.
 
Psi Baba said:
The short answer is that it had much to do with man's ancestors finding themselves on the wrong side of the great rift in Africa which put them in a grassy steppe instead of in a forested or bushy region.
Click to expand...
Not if the Toumai skull really belonged to a biped, it didn't.
 
Beady said:
I'm told that, over long distances, a human can outwalk a horse. Not sure how true this is, but it would be a good illustration of the point if you can substantiate it.
Click to expand...
In David Atenborough's "Life of Mammals" there's a cool part where they show San tribesmen hunting a large herbivore (don't remember what it was...).

Anyway, the tactic they were using was to just exhaust it by chasing it for a long time. At one point one man alone follows it for hours on end. Eventually the animal colapses from exhaustion.

I thought it was neat.
 
I don't think it's all that clear why bipedalism evolved. There've been a lot of ideas proposed.

I've seen it suggested that it was to carry food (to store for oneself, to give to one's mate, relative, or friend). To use tools. So that men could better show off their penises and women better conceal their genitals. To keep less body area exposed to the sun. To keep the hands free while collecting and eating food (sqat feeding) which prepared us for later evolution of true bepedality. To get a better veiw of predators. Because it became fashionable to walk bipedaly, and those who were better at it had more offspring.

The point is that I doubt we'll ever be able to differentiate between the above, or other explanations. The best we can do is rule some of them out. One or all might have had some part to play in the evolution of bipedality.
 
Humans did not evolve an upright posture.
Australopithecines did.
Or their ancestors did.
Whether we got it from them is open to argument, but likely.
Whether they developed it on the ground, or like gibbons , learned to walk upright on branches while holding onto higher branches with their hands, simply is not known.
 
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