Jane Goodall made an interesting observation about the chimpanzees she studied: she found that nearly 50% of the fatalities she observed were due to infants falling to the ground as the mothers they were clinging to moved through the trees. This was one of the bases of C Owen Lovejoy’s interesting (and largely unknown today in popular Paleoanthropology) theory that bipedality in the human lineage evolved primarily because it greatly reduced this source of mortality.