Human Body Proportion

Not really sure of the question, but you might get some help from Leonardo DaVinci's Notebook. I'm not sure of the exact spelling, but it provides some really good insights, at least from an artistic standpoint. Might help; might not. Probably not, but it's worth a look-see if you can find a library copy.

This and the referenced sources should give you a good start:

http://en.m.wikipedia.org/wiki/Human_skeletal_changes_due_to_bipedalism

http://ngm.nationalgeographic.com/print/2006/07/bipedal-body/ackerman-text

Years ago I read something about the body´s shape.
You should be able to reach around your wrist with your fingers.
Your neck should be twice the size of your wrist.
Your waist line again should be 3 or 4 times your neck.
The length of you head should be 1/7 of your body
Every detail was like that.
Maybe it really is supposed to be like that or
maybe it is the perfect body in some century long ago
maybe it has to do with Leonardo da Vinci

Study your body.
The toes sit in the right spot for wlaking.
Spreading the toes give a better grip
bown your knees and you will see you can rest without touching earth
kneel and you can rest on your heals
etc etc

You should go back into developmental biology to see why such things as extremities have these lengths.
Neil Shubins 2005 book Your Inner Fish discusses the evolutionary significance of extremities in lower species and how this affects our own structure.
Hes a paleontologist but because of his unique perspective, hes chairman of the dept of anatomy at the U of Chicago Med SChool.

I think a lot of it can be traced back to when they started delivering pizza.

Yeah, I already tried to read about that.... Instead, it's the first thing come in my mind. But, no luck... Thx 4 your suggestion .

Wow. Thank you very much. It's really close to what I'm looking for. You are so helpful.

Thank you for your help. I'll try to look for the book.

I'm not sure I understand the focus of the question exactly, but here are a few thoughts...

Our basic body plan comes from the fact that we are evolved primates, so our body plan over this period of evolution wouldn't be expected to deviate from the basic plan too much.

Beyond that there are some very basic forces which affect the limits of all organisms. For example, insects can only get so large in their current environment due to respiratory and exoskeletal limitations. Likewise, human leg bones are not going to get so long that they become a liability by breaking all the time. So stable body proportions which make us robust and functional within our environment are going to be our limiting factor.

I'm not sure I've done more than state the obvious with all that, which makes me think I still may not understand the question. Perhaps if you could provide more examples we could focus our answers more accurately.

First thank you for your response and sorry for my confusing question. Well, I'm not good in English, so it's a little hard for me to explained it more detail. But, here are some examples/explanations which maybe can help you to understand more of my question.

Some references says that our body proportion have a basis, and it must be fullfilled to be called an ideal body. Like Leonardo Da Vinci in his Vitruvian Man painted in rectangtular and circle line, or 7-8 heads theorem which counts the body size using heads as the unit, etc.
Another example is like what @saab said above....

What I want to know is simply why ??
You said that if our leg bones get so long it will be fragile, right? then in your case, I want to know, what is the ideal length and why??? in what basis you can say that it's too long or it's to short.... Same case with the hand, body, and etc lengths.
Another example, in my first post I said that why our leg have to be longer than our hands... What's wrong if the hands is longer??? who knows maybe in the past it is supposed to be like that.

When you said "stable body proportions", means there must be some researchs that had been done.... That's why they can know It's the most stable, right??

I want to know the reasons..... that's all.

One more thing, for your information. I'm doing this in my research for my thesis. I'm making a humanoid robot of human size in 1:5 scale, roughly. And my supervisor want me to find an explanation from human body relationship to the stability of the body.
Why our hands size have to be in range between xxx cm- xxx cm, same question for the legs and the other parts of body.

This is the reason why I'm asking this. I tried searching it through libraries and internet. They give me the ideal size number for a human body... but no reason written why It supposed to be like that.

I hope this can make it clearer. Thank for your attention.

There are many forces at play in body plans.

As to why our (and other animals bodies) are proportional in relation to some of their own structures (which I think is the main thrust of your question), I would guess that physics is one of the forces involved as well as genetics which carries symmetry. If you're asking specifically why humans have the body proportionality that DaVinci observed, and why those proportions seem to align with simple geometric shapes (square and circle), then I guess I don't really know. I would note however that humans are adapted for intelligence and tool making rather than for extreme body performance. I would bet that an Orangutan would proportion out very differently in a Vetruvian Man diagram. And I believe there is an underlying selective force in nature which selects for "simplicity" over specialization unless there is overwhelming benefit from the specialization. Because of this, it may be that human proportionality seeks some equilibrium of simplicity when overriding physical specialization is not present.

As for proportionality between species I would say that selection is the driving force. For example, Giraffe's necks and legs are very long and in some sense provide a liability for them. It makes it difficult for them to drink water for example. But over all they must get more benefit from those structures than liability or the genes for them would not have accumulated in the gene pool.

That's a difficult challenge. I don't think Da Vinci himself could figure out why the proportions of the human body are the way they are, he only observed them.

If I had to guess I would say that the underlying reason comes down to the physics of how bones and muscles function best in earth gravity and based on the survival needs of the organism. Because humans are not specialized for extreme physical requirements our basic body plan may tend toward a neutral equilibrium in which simple physics takes precedence within natural selection.

There is also the possibility of a sexual selection bias in which "golden" proportions are perceived as more attractive and therefor more likely to reproduce. There are probably whole studies related that that possibility.

Yeah, what you said makes sense. Thank you very much for your help. Your opinions had open a new side of my point of views... I'm really appreciated it.

Thank you once again, and it's nice to talk with you. I'll try to search some more in other sources.

http://sci.waikato.ac.nz/evolution/HumanEvolution.shtml

Glad I could help. Good luck. Come back if you need more help.

True. I wanted to say something, and that's all I had.