Evolution and Building Products

I have developed a new theory to explain how bipedal humanoids evolved from lower orders of primates that walked on all four limbs.

My theory is based upon recent findings that apes "show engineering skills when building", in the words of the BBC. According to the research, published in the Proceedings of the National Academy of the United States of America:
Nest-building orangutans demonstrate engineering know-how to produce safe, comfortable beds

Nest-building orangutans must daily build safe and comfortable nest structures in the forest canopy and do this quickly and effectively using the branches that surround them. This study aimed to investigate the mechanical design and architecture of orangutan nests and determine the degree of technical sophistication used in their construction. We measured the whole nest compliance and the thickness of the branches used and recorded the ways in which the branches were fractured. Branch samples were also collected from the nests and subjected to three-point bending tests to determine their mechanical properties. We demonstrated that the center of the nest is more compliant than the edges; this may add extra comfort and safety to the structure. During construction orangutans use the fact that branches only break half-way across in “greenstick” fracture to weave the main nest structure. They choose thicker branches with greater rigidity and strength to build the main structure in this way. They then detach thinner branches by following greenstick fracture with a twisting action to make the lining. These results suggest that orangutans exhibit a degree of technical knowledge and choice in the construction of nests.
So how does this explain the evolution of humans that walk on the ground instead of climbing in trees?

Simple -- How else could a sales rep deliver samples if the rep had to use all four limbs for climbing.  ;-)
Artist Unknown
www.pnas.org/content/early/2012/04/09/1200902109.abstract?sid=98ebca9d-e99b-499e-aaf3-84536cf7d36f, accessed 2012-Apr-16, 

Authors: Adam van Casteren, William I. Sellers, Susannah K. S. Thorpe, Sam Coward, Robin H. Crompton, Julia P. Myatt, A. Roland Ennos