What evolutionary mechanism caused hominids to walk erect? I mean, what evolutionary advantage did they gain? I know ultimately it allowed us to play in marching bands, but what competitive or developmental advantage was gained? Were we we faster? Better hunters? Better reproducers? Or was it the tool making/using that could only come from erectness?
Try picking up a book by Elaine Morgan. She wrote the original “Aquatic Ape” book, and also one called “The Ascent of Woman” (although there has been a later book by somebody else with the same title, about the Suffragette movement).
Lots of Primates walk on their hind legs. But you only really need to stand upright if you spend a proportion of your time in water. Funny things happen to you if you spend a lot of time in water - I mean, as a species. Your body fat rearranges itself. (Human body fat is very different from other primates.)
You tend to lose your body hair. (Some people more than others.)
Just supposing that women spent a lot of time in water, if they were carrying babies their breasts would have to be accessible to the baby without them leaving the water. And they’d need to have some way of stopping the infants just drifting off with the waves. Good thing kids come with that grasping reflex, and that the Males tend to favour women with long hair, for some reason.
And Humans cry. It’s an emotional response, sure, but physiologically, it’s a mechanism for getting salt away from the eye. The only creatures that have this are seabirds, elephants and humans. And elephants are the missing link between pigs and whales. Ever hear about elephants swimming around the Islands in the Indian Ocean? They do. They use the trunk as a snorkel. A few million years hence, that trunk will be a blow-hole on their back.
The evolutionary advance offered in being able to stand upright is the ability to breathe while standing in water out of range of the kind of predator that would skin you alive if you were standing on dry land.
N.B. This hypothesis makes perfect sense to me, but is still not widely accepted in paleontology circles.
I saw a TV show about this a while back. I really like water and I liked the thought of this. I also remember something about the hair on our bodies being hydrodynamic.
The theory that I am familiar with is that standing up allowed us to manipulate objects with our hands, way back when we were tree-dwelling scavangers. This would lead to out ability to manipulate tools and the like. Another thing I have heard which may or may not have something to do with bipedal motion is that humans are the finest marathon runners in the animal kingdom. I’ve a feeling this might be bollucks though.
One evolutionist I talked to told me he believed people began to walk upright due to a need to see farther. You can see farther the higher up your eyes are.
Most of the things presented are current theory. Truth is, they’re probably all true in some respect. Just because you can’t neatly describe the evolutionary advantage of something in less than ten words doesn’t mean it doesn’t have a significant advantage. So, most probably: there are lots of very small evolutionary advantages to walking erect. Many primates spend at least some of their time walking erect, humans just took full evolutionary advantage of bipedalism.
Another interesting controversy about this: anthropologists spend a lot of time arguing about whether our larger brains happened before or after our bipedalism. Some think that bipedalism sparked the need for a larger brain, and some say that a larger brain gave us the capacity for exclusive bipedalism. It’ll probably crop up somewhere in the archaeological record, at some point.
I don’t think anybody knows why we walk erect.
No settled theory. Congratulation’s idea of multiple
advantages makes sense.
The scenario is that forests recede for some reason
and these apes, tree dwellers, faced with receding
forests, shift upright. Why? First, they can see
further across the grasslands–they already have
good vision and this enables them to exploit it
better. Second, they can travel further, also an
advantage, as food isn’t as close by. Third,
it frees their hands.
Bipedalism is about as good a way of getting about
as being four-legged, and these critters needed
to be mobile. As they were probably already able
to walk upright sometimes, the advantage was
to stay up, not go back to four legs–given the
other advantages.
I think it is widely thought that the human body evolved
before brain size went up significantly. You don’t need
a bigger brain to walk upright and austropithecanthropus,
we’re talking what, 3 million years ago, has a small brain
(though how small I don’t remember). These are little
fellas, by the way.
How and why human intelligence evolved is at least as
baffling a question. I mean, the intelligence required to
do calculus and physics was online 100,000 years ago, maybe.
Why?
It happened the day after we got our asses kicked by that upstart tribe from across the plain…
I seem to remember waking up and seeing this…thing…
it was some kind of big, black, square, smooth object that emitted music by Gyorgi Ligeti…next thing I know I was picking up this bone…
I wouldn´t even try competing with a horse! 
On the other hand, I´ve seen very few horses in the olympic marathon race.
Hmmmm…I was once told that wolves can trot for hours on end, so in a sense they would be the marathon runners of the animal kingdom.
My view on the upright stance and brain development… I think it’s entirely possible that they developed together, not separately:
Evolution can be thought of as simultaneously occurring changes that compliment one another.
For example, the pretty much hairless ancestors of the Wooly Mammoth probably had a few somewhat hairy individuals born each generation. That hairiness was just an unusual trait that gave them no advantage–until the climate started to shift at the beginning of the ice age; then those with a bit of body hair were better able to survive (ie…add to the gene pool). Each generation after that, those born with the genes responsible for hairlessness would be at a disadvantage and would likely die off early–with very few oppurtunities to pass on that set of genes. Eventually the genes for hairlessness would be completely eliminated from the gene pool, as more and more young with the gene for hairiness would be born until that trait became a dominant feature of the species.
Likewise, I imagine that an upright stance occurred every so often among our ancestors but was more or less an aberration…until some change in the environment made it a very handy trait to have. And of course, every generation has a few individuals who just seem to do things differently—so a few of the upright-walkers would’ve had the capacity to understand that they had an advantage and to use it best. Those individuals who had both the upright stance and the brains to put it to good use, were the ones who would’ve survived and reproduced best…passing on the characteristics of intelligence and upright stance.
I don’t have the answer, but I remember in one of my college classes we discussed neotony. We have a lot of DNA in common with other apes, and a lot of the differences are due to when genes turn on and off. Baby chimpanzees have their necks and heads arranged like humans, as if they were meant to be more upright. Then as they mature it changes. We retain a lot of the same appearance that baby chimps have throughout our lives. Neotony was supposed to explain this, that we are more alike to infant chimps, but certain genes switch on or off and then we differ.
All that was just to say that it was probably simply a mutation of these switches. And that mutation provided some benefit that allowed us to survive. After all, we do pay a price for our uprightness in that our spines are not built to withstand so many decades of this posture, and that’s why many older people have back problems.
The horse is what came to my mind too when I read this. A Tennesse Walking Horse can keep up a flat walk ( 5 to 7 mph) all day long with little effort. It seems like that would be an advantage in a marathon. And the wolf at around 5 mph,has already been mentioned, certainly a contender.
None of which has anything to do with why we are upright? 
I can walk at 2 or 3 mph for the entire day, minus time to sleep. And I could keep going for weeks or months if necessary.
Odd! When we hike we are lucky to get 6-7 miles in a day…
Assuming we manage to break camp by noon.
What would be real early 
How did he explain the giraffe?
Everyone has overlooked the most obvious advantage of bipedalism . . . it’s impossible to get a good fit in clothing in quadrupedal stance.
That’s largely a good way of thinking, but some of the specifics are off. Remember, bipedalism is not genetic, it’s a behavior. There are genetic traits that make bipedalism easier (rotated pelvis, anterior foramen magnum, bicondylar angle), and these are things that would be selected for once bipedalism became a useful practice. So environmental pressures make bipedalism a healthy alternative to quadrupedalism, which in turn means that genetic traits that predispose a person to bipedalism are selected for. So your explanation is on the right track, but incomplete.
Well, Australopithecus was a little fella, which makes his brain size larger than you’d expect relative to his body size. He may have been a smart little dude.
That’s a good (if sort of unanswerable) question. Remember that the species-defining characteristic of humans is the capacity for innovation. The major thing that’s kept us alive and thriving is our ability to adapt, using culture as a front-line defense against environmental pressures. The ability to innovate requires intelligence.
Here’s wiki (human evolution) on this:
The fossil record seems to indicate that Australopithecus is the common ancestor of the distinct group of hominids, now called Paranthropus (the “robust australopithecines”), and most likely the genus Homo which includes modern humans. Although the intelligence of these early hominids was likely no more sophisticated than modern apes, the bipedal stature is the key evidence which distinguishes the group from previous primates who are quadrupeds. The morphology of Australopithecus upsets what scientists previously believed, namely, that large brains preceded bipedalism. If A. afarensis was the definite hominid which left the footprints at Laetoli, it strengthens the notion that A. afarensis had a small brain but was a biped. Fossil evidence such as this has made it clear that bipedalism far predated large brains. However, it remains a matter of controversy how bipedalism first evolved millions of years ago (several concepts are still being studied). The advantages of bipedalism allowed hands to be free for grasping objects (e.g. carrying food and young), and allowed the eyes to look over tall grasses for possible food sources or predators. However, many anthropologists argue that these advantages were not large enough to cause bipedalism.
…
Climate changes around 11 to 12 million years ago affected forests in East and Central Africa so that there were periods when openings prevented travel through the tree canopy, and at these times ancestral hominids could have adapted the upright walking behaviour for ground travel.
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Most species of Australopithecus were not any more adept at tool use than modern non-human primates, yet modern African apes, chimpanzees, and most recently gorillas, have been known to use simple tools (i.e. cracking open nuts with stones and using long sticks to dig for termites in mounds), and chimpanzees have been observed using spears (not thrown) for hunting. However, Australopithecus garhi some have argued that A. garhi used stone tools due to a loose association of this species and butchered animal remains.
I don’t know…I never asked him about giraffes. Sorry.