Short and sweet -
A practical 'object' lesson: Which is strongest – A circle/sphere or a an equilateral triangle/pyramid?
It depends on what the loading is, a sphere will resist uniform pressure better (as in a compressed gas tank or submarine) though a sphere is often not the most convenient or easy to build, so a cylinder (also based on the circle) is more common.
A triangle can resist a point load better (if applied to a vertex) and combinations of triangles (trusses) are very common in construction.
If an engineer combines the two, see Buckminster Fuller...(and Leonardo da Vinci) there you have it. And this exact concept is seen in creation - the bone structure matrix:
Bone structure and function*
*As a side note, an interesting one at that, Calcium the element that most makes up bone matter is classified a METAL...http://wiki.answers.com/Q/Why_is_calcium_classified_as_a_metal#page2
Next: What is 'dark matter'?