Willow trees bend, cottonwood trees break. God has designed our bones with a perfect balance between strength and flexibility. Consider this article by Dr. Randy Guliuzza: “Inside, a three-dimensional network of small boney material resembling a porous sponge, called spongy bone, is found throughout small bones and at the ends of long bones. Spongy bone absorbs shocks and also contributes inner bracing or stiffness. The thin bony inner bracing elements do not grow randomly, but look and function like the support struts in the Eiffel Tower. Some studies demonstrate that if engineers apply a stress-strain analysis to a cross section of bone, it reveals that the boney braces are built along lines of maximum stress relative to the mechanical forces applied to them.” If our bones were solid, they would too heavy for us to move easily. Hollow bones would not be as strong, nor would they produce blood cells as the marrow does. God uses great efficiency in His designs.
Guliuzza, Randy 2009. “Made in His Image: Bone, An Engineering Marvel” ICR Acts & Facts. 38 (7): 10.