Fig. 3. View from the top of pelvic inlets of Pan, Lucy (AL 288-1) and Homo. The anteroposterior (AP) diameter is widest in Pan which changed to platypelloid in Lucy whose widest diameter is the transverse diameter due to adaptation of bipedal gait. The increase in fetal head size increased the size of birth canal of Homo mainly in anterior region but the maximum diameter still is transverse diameter. The fetal head enters the Pan pelvis in AP dimension but transversely in Lucy and Homo.