Alright, in order for the ancester of the moder human to walk upright, he had to alter the size of his pelvis, which meant than babies couldn't be in the womb as long or they wouldn't be able to get out, and due to the structure of the body, all the weight was forced upon two legs. All these things apear to be negative traits, but if it's still around today, it must have a positive aspect. So my question is what are the benefits of walking upright.
Evolution II
- Thread starter Enigma'07
- Start date
No creature is ever a "finished product", although some things - like crocodiles - haven't changed very much in the last few million years.
The adaptive significance of bipedal motion - that you can use your hands for other things than walking - pre-dates bipedal motion in climbing creatures. We are, effectively, a creature partway between climbing and walking. Our social development (not evolution in the genetic sense) has told most of the story of human development since we discovered/invented any sort of technology.
The adaptive significance of bipedal motion - that you can use your hands for other things than walking - pre-dates bipedal motion in climbing creatures. We are, effectively, a creature partway between climbing and walking. Our social development (not evolution in the genetic sense) has told most of the story of human development since we discovered/invented any sort of technology.
Briefly, the shape of the pelvis of the last common ancestor of humans and chips was somewhat more human-like than chimp-like, or better, it was more gibbon-like, because this ancestor was arboreal. Gibbons (and other arboral simians) natural tendence when not in trees is to walk upright. While terrestrial simians had adapted to quadrupedal locomotion, human ancestors had still being bipeds, improving the bipedalism by enlarging a bit the legs while losing their adaptations to arm-swinging in the trees, by reducting the long arms (and at the same time making bipedal locomotion easier, without those unusefully long arms hitting accidentally everywhere).
Also I've never heard of this thing of bipedal locomotion requiring a alteration of the pelvis's size. The improving of bipedal walk when human ancestors were not primarily arboreal anymore probably led to a alteration in the shape of the pelvis, but not significantly in the size. I think that the gestation time did not shortened, I guess that in fact it got longer, making possible brain development to go further, and then, requiring a bit of enlargement on female pelvis.
But, really, walking upright brings a bunch of probles to tetrapods that mostly had locomoted his spines horizontally. There are the spine problems itself, and other problems such as gravity and what it does with the female vertical standing bodies in pregnancy, I do not know detailed, but there are problems with that. The advantages had to pay the problems, or else it probably would had not be selected. "Lucy: the begginnings of humankind", by Donald Johanson and Maitland Edey explains better than me the hypothesis of Owen Lovejoy that the way to bipedalism led to beings that can have more offspring than arboreal beings, in a positive feedback way.
Basically, being bipedal is a inneficient way of locomotion - it's not faster or economical than quadrupedalism to the same range/time - but with this came things like females being capable of take care of more than one child at once, because that's easier and safer to do in the ground with kids that are not faster than you. The fall from the ground to the same ground is certainly less harmful than the fall from the tree. That's the main point, the more numerous offspring. But with this is hypothetized that a lot of typic human characteristics came together, such as monogamy and the absece of determinant heat on females, the roots of family nucleus, more sociability and etc.
Also I've never heard of this thing of bipedal locomotion requiring a alteration of the pelvis's size. The improving of bipedal walk when human ancestors were not primarily arboreal anymore probably led to a alteration in the shape of the pelvis, but not significantly in the size. I think that the gestation time did not shortened, I guess that in fact it got longer, making possible brain development to go further, and then, requiring a bit of enlargement on female pelvis.
But, really, walking upright brings a bunch of probles to tetrapods that mostly had locomoted his spines horizontally. There are the spine problems itself, and other problems such as gravity and what it does with the female vertical standing bodies in pregnancy, I do not know detailed, but there are problems with that. The advantages had to pay the problems, or else it probably would had not be selected. "Lucy: the begginnings of humankind", by Donald Johanson and Maitland Edey explains better than me the hypothesis of Owen Lovejoy that the way to bipedalism led to beings that can have more offspring than arboreal beings, in a positive feedback way.
Basically, being bipedal is a inneficient way of locomotion - it's not faster or economical than quadrupedalism to the same range/time - but with this came things like females being capable of take care of more than one child at once, because that's easier and safer to do in the ground with kids that are not faster than you. The fall from the ground to the same ground is certainly less harmful than the fall from the tree. That's the main point, the more numerous offspring. But with this is hypothetized that a lot of typic human characteristics came together, such as monogamy and the absece of determinant heat on females, the roots of family nucleus, more sociability and etc.
paulsamuel
Registered Senior Member
I get a little angry at speculations like these. There's just a guy with scientific credentials speculating about the advantages to being bi-pedal and calling it evolutionary analysis. My question is, Where's the data?!!!!!???Danniel said:
...I do not think that's a quite satisfactory, but at least is a reasonable assumption, better than leaving a enormous theoric gap. I think that the more relavant data is the difference of the quantity of offspring of humans and arboreal and terrestrial apes. Maybe totally arboreal can have a bit less offspring than terrestrial, and terrestrial quadrupeds can have less than terrestrial bipeds, than were inferring and veryfing what can cause these differences, such as the difficulty to take care of multiple offspring up in the trees, and other sort of observations of the costs of parental caring in terrestrial apes... altough I'm just suposing this, I've only read the book, I do not know if there's any "official" paper at all about this...paulsamuel said:
to add to the original post: in order to stand in an upright posture, the shape and position of the pelvis had to change. it became longer and narrower as opposed to the spread tilted shape that allowed for walking on all fours. gestation period had to decrease as the narrower birth canal wouldn't have been able to accommodate babies of the same size. babies had to be born earlier and were more dependant on their mother for a longer period of time. why is this important? because mothers who were receptive to their mate all year long kept them around as protection and food providers, resulting in more successful offspring. mothers who were only receptive during estrus had less successful offspring...they had to find their own food and fend off predators all while caring for young helpless babies. that doesn't work so well. so thank your ability to walk upright for our human year-round sex.
paulsamuel
Registered Senior Member
Danniel said:
My problem with it is that it's misleading. The lay public with a passing interest in science may give this speculation more credence than it has, given that it's just speculation. Crap, any armchair anthropologist could do that, with no data!
Did you ever here of "just so" stories. Look it up, it's worth the analogy.
Heh, I didn't knew those stories... I see what you mean. I prefer to stick with most obvious things only, such as the thing of already being bipedal when arboreal, and then just suffering minor stretch and shrink adaptations to walk on the ground, unecessarily associated with any other thing. The other stuff I prefer to leave as just whatever evolution had done, probably mainly by natural selection.paulsamuel said:
But I still like Lovejoy's hypothesis, even being impossible to say that was definitely that what happened (and at the same time impossible to say that didn't I guess, what's some problem), still a plausible, totally natural explanation to much of our uniqueness. It's specially interesting to show to some people that argue that human evolution isn't yet explained ("we evolved too fas" is common), being a special mistery in nature and filling the gap with astronaut gods or something like it. I prefer that people recently interested in science to give credance to that than Daniken stuff.
I always figured it was a combination of a few things...
We left the forests and jungles to explore and eventually settle outside.
After settling communities ouside the abundant lush vegitation, we began eating more meat because that was more readily available since we had not begun to cultivate crops yet.
Our communities began growing in size.
The more animals you have in a group, the more food you have to supply.
If you are running after a wild boar with a spear it seems like it would be a benefit to have your hands free.
We left the forests and jungles to explore and eventually settle outside.
After settling communities ouside the abundant lush vegitation, we began eating more meat because that was more readily available since we had not begun to cultivate crops yet.
Our communities began growing in size.
The more animals you have in a group, the more food you have to supply.
If you are running after a wild boar with a spear it seems like it would be a benefit to have your hands free.