After checking his work the animal climbs up and lies down for sleep or rest. In regard to the physical evolution, in particular to the erection of the body the hands freed from use in locomotion, the distinction of arboreal and terrestrial environments in the habitat is of great importance, as is the transition from one to another in evolutionary theory. But it has been little noticed that nestbuilding is represented in both environments and that it shows different technical characteristics. In the case of the tree nest some strong horizontal branches are enough to support the platform. Stability is provided by the physical conditions of the tree.
Variation is limited by a limited situation.
In contrast to this the materials offered on the ground are of much greater variety and this variety is accessible. The groundnests are therefore more differentiated in terms of construction and form. They vary from heaped types on the ground to woven structures on bushes and to stable and vertically standing structures. This typology can be interpreted in terms of an elementary evolution. The bamboo tower certainly resembles human structures.