It is typically thought that the diets of early "Homo" had a greater proportion of meat than "Australopithecus", and that this led to brain growth. The main hypotheses regarding this are: meat is energy- and nutrient-rich and put evolutionary pressure on developing enhanced cognitive skills to facilitate strategic scavenging and monopolise fresh carcasses, or meat allowed the large and calorie-expensive ape gut to decrease in size allowing this energy to be diverted to brain growth. Alternatively, it is also suggested that early "Homo", in a drying climate with scarcer food options, relied primarily on underground storage organs (such as tubers) and food sharing, which facilitated social bonding among both male and female group members. However, unlike what is presumed for "H. ergaster" and later "Homo", short-statured early "Homo" were likely incapable of endurance running and hunting, and the long and "Australopithecus"-like forearm of "H. habilis" could indicate early "Homo" were still arboreal to a degree. Also, organised hunting and gathering is thought to have emerged in "H. ergaster". Nonetheless, the proposed food-gathering models to explain large brain growth necessitate increased daily travel distance. Large incisor size in "H. rudolfensis" and "H. habilis" compared to "Australopithecus" predecessors implies these two species relied on incisors more. The large, "Australopithecus"-like molars could indicate more mechanically challenging food compared to later "Homo". The bodies of the mandibles of "H. rudolfensis" and other early "Homo" are thicker than those of modern humans and all living apes, more comparable to "Australopithecus". The mandibular body resists torsion from the bite force or chewing, meaning their jaws could produce unusually powerful stresses while eating.