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Why did humans straighten up?

1. IfIAmNotWrong, Humans are one of the few animals able to hold a spear/Javalin in the hand. And we holds world record to be able to throw them far in the animal kingdom. This gives a strong indication of the purpose of our unique ability of our body.

2. It is difficult to move on all four carrying a long stick (spear). Better to carry it away from the ground and away from obstruction.

3. I find it easier to imagine human using spear as a defensive weapon. Unless you can throw one spear at predator and kill it, it seems to make sense to hold on to a spear, point it in the direction of the predator.
It is easier to hold it a long stick with 2 hands than one.

4. To be able to survive a "stand-off" long enough you must be able to hold it long enough.

5. To walkaway from a "stand-off" with a predator you'd have to hold your spear up all the time.

6. Human stand taller to "intimidate" Predator to stay alive.
http://www.fs.fed.us/r6/olympic/aboutonf/aboutonf.htm
"If approached on the trail by cougars, stand your ground, make eye contact, and do not turn your back. Making loud noises and making yourself appear taller by staying on higher ground seems to intimidate them. With bears, stay calm, give them plenty of room and make loud noises to discourage them."

7. The younger you are, the greater the chance that standing upright make you taller than a dog, hyena, wolf, fox, leopard.
 
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The thing with evolutionary pressures is that there is often no single 'cause' behind an adaptation. In an environment, if a physiology or a genetically inherited trait does not detract from its fitness in some small way, it tends to remain part of the gene flow. If it gives even a small amount of competitive edge, then overall those who have the trait might have (on average) proportionately a few more offspring in a lifetime.

We know one thing; a common ancestor of modern humans evolved a series of traits that allowed bi-pedal locomotion. Any suggestion that might of influenced it probably did have a small impact on the fitness of the organism somewhere along the line. The tricky part is considering any factors that might have impeded it.

Athon
 
I think the tools explanation is a chicken/egg argument. Did we stand up to use tools or did we start to use tools because we stood up? Personally, I believe the latter.
 
Or did we stand up somewhat, find that our hands were free to use tools, and then spend more time standing up because of it?
 
Starthinker said:
I think the tools explanation is a chicken/egg argument. Did we stand up to use tools or did we start to use tools because we stood up? Personally, I believe the latter.
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It's neither, since other animals besides ourselves are able to use tools. In fact, given the anatomy of the apes' foot, they are probably more dexterous than we are, and therefore are more physically adept at tool use. What makes us more advanced is our ability to use tools to greater purpose.

Tool use had absolutely nothing to do with our standing erect. If it had played any part at all, we would have kept opposable thumbs on our feet and instead have developed wider asses for a more-stable platform, so we could wield hammer and tongs with all four "hands" at once.
 
Uh, I'm not trying to be a damp towel or anything, but we don't have to posit one reason for all phases, or even multiple reasons for one phase. That's the whole problem with the "unfit intermediaries" argument from ID. Standing could have developed before walking, simply because it is useful to stand up. Once standing, those that could still move well while keeping this benefit would have fared still better, as they could have both the benefit and have less effort moving relatively well. In the plains it pays to be on the move, as forage does not sit still, so moving relatively well over long distances paid off as well. We have the beginnings of bipedalism.

It could have been a series of steps, independant of the final "purpose" of bipedal motion; simply modification of what otherwise was a beneficial trait. In other words, bipedalism is not an all-or-nothing has to happen all at once (partially bipedal, then fully bipedal), but a series of modifications that could each have had their own uses, like energy conservation or being able to use tools standing or rearing up being a survival trait before truly efficient gait.
 
BTW there was a study that bipedalism is a far more efficient form of locomotion than knuckle walking. When our ancestral ape was faced with the need to move longer distances due to environmental changes the choice was not between galloping like a horse and bipedalism. It was between moving like a chimp and bipedalism.

I think the human lineage is the only primate group that travels long distances . (I could be wrong, not being a biologist)
 
athon said:
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.
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A packet a day, maybe. One per year, I have a hard time believing that would be a sufficient cause to evolve upright locomotion. Surely the speed advantage of all fours would vastly outweigh the savings of one medium-sized meal per year. Heck, reducing the average height/size by a millimeter or two would probably save more energy per year.
 
Beerina said:
A packet a day, maybe. One per year, I have a hard time believing that would be a sufficient cause to evolve upright locomotion. Surely the speed advantage of all fours would vastly outweigh the savings of one medium-sized meal per year. Heck, reducing the average height/size by a millimeter or two would probably save more energy per year.
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Saving one pack a day! Hell, we would hardly have been able to find that much, let alone save. There's quite a few calories in a pack of chocolate biscuits.

Besides, that's not the point. Even a small amount of energy saved will give an advantage. Think of it this way; imagine a competition where two people are identical. They have to fight over £1. Over 1000 trials, you'd expect that they would each have £500. Sure, there'd be other factors at play and so it's likely that due to pure luck one might have a little more than the other. But for arguments sake, you would imagine £500 a piece.

Now, let's say that I make the other a tiny bit faster. Just a little. That might give him enough of an edge that he might get £502, while the other guy only £498.

That's only £2! Hardly anything (it's basically a pack of biscuits!). But, in a competition, that is better than his competitor. It might mean enough to have one more baby in a lifetime, while the other guy might not.

Time will multiply this out. In a competition for resources, having 502 babies that have your trait versus 498 babies without is still in your favour. You now dominate the gene pool, and for as long as that tiny advantage exists, your numbers will climb little by little over subsequent generations (barring any misfortune).

Several calories a year advantage is still an advantage.

Athon
 
So, how big of a packet of biscuits are we talking about here?

(And I assume y'all mean "biscuits" in the British sense of the term, i.e. what we Yanks call "cookies." What an American calls a biscuit is this dry, crumbly, often hard thing that evokes images of burly lumberjacks, who only eat them to show off how tough they are.)
 
There is also the "aquatic ape" theory.

http://www.aquaticape.org/

The Aquatic Ape Theory (often referred to as the AAT or AAH) says humans went through an aquatic or semi-aquatic stage in our evolution and that this accounts for many features seen in human anatomy and physiology. Using the principle of convergent evolution, it says that life in an aquatic environment explains these features, and that a transition from ape to hominid in a non-aquatic environment cannot.
 
Upright walking allowed us to have a variety of ambulations including walking, running, crawling, climbing trees or mountains, swimming, (not to mention a wide variety of sexual positions) besides allowing us to carry and use weapons while walking or running. The question I wonder is why did we loose the tail. I could use an extra appendage quite often.
 
force_redo said:
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
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I think also that bipedal motion is potentially more energy efficient, at least in the human size range.
 
Ziggurat said:
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.
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I would have some argument with the "facts" on that website.

Endurance riding is my sport and i have studied horses at university. It is a subject that I do know a little about.

BTW, it is highly unlikely the horse shown in the picture was the one involved but that's not important.

A fit endurance horse can easily maintain 20Km / hour average for 80 Km depending on terrain and weather conditions. The horse would not have HAD to stop for an hour to eat drink and rest. It would probably have drunk a couple of times during the ride, maybe 5 mins each time, it is highly unlikely that it would have eaten and one stop at the halfway point for maybe 20 minutes, (depending upon tests of heart rate, temperature, dehydration tests and so on). I would say that 5 hours would definitely be a MAXIMUM time for any moderately fit endurance horse and they have some of the best in the Emirates, we breed 'em right here in Oz :)

I guess the point I'm trying to make is, read stuff on web pages with some skepticism.

ETA: Just to show you I'm not completely full of it, you can read the results of a famous Oz endurance ride from last year here:
http://www.abc.net.au/rural/sa/features/safeatures-tomquilty2004.htm
 
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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.
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This mainly comes down to thermoregulation; that is, the ability of an organism to dissipate heat while engaged in activity. Humans are very good that this. When you combine our efficient upright walking with perspiration that is uninhibited by fur, you have an animal that is very well adapted to travel.

Many other animals are physiologically incapable of thermoregulation during strenuous activity, mainly due to the fact that they can't pant very well (if at all) while using their front/upper bodies for locomotion.

Horses are a worthy competitor in this arena because they sweat. However, their hair makes this mechanism less efficient than it could be so even they must take breaks to cool down. Whether or not a human could catch a horse comes down to whether or not the horse's cycle of rest and movement can still outpace the human's slow and steady advancement. The answer is that they tend to be a pretty close match.
 
I would think that part of the comparison of endurance between horses and humans should involve the fact that humans can carry food and water, and consume them while walking. The horse? Not so much.
 
ImaginalDisc said:
I would think that part of the comparison of endurance between horses and humans should involve the fact that humans can carry food and water, and consume them while walking. The horse? Not so much.
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Like any of these sorts of comparisons there are a whole host of qualifiers and exceptions and "ifs" and "buts" that can be applied. So much so that I'm not sure any such comparison is of any value.

Here are a few for example.

Are you putting an olympic level marathon runner against the horse?
Is the horse some old nag out of the paddock or is it an ultra fit endurance champion?
Is the horse carrying somebody or not?
What breed of horse are you using?
What distance are you talking about?
What rules apply?

A human marathon race is, from memory, about 42 Km.
The shortest official endurance ride is 80 Km.
Which distance are you going to use?

...and so on.
 
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