CARRIER, David/R: Functional Tradeoffs in the Running and Fighting of Early Hominids

Characters that enhance fighting ability often limit locomotor stamina. Some of the characters that distinguish Australopithecus and Homo (e.g., limb and trunk proportions and robustness) may reflect a dichotomy between selection for fighting ability versus selection for locomotor stamina. We are studying functional tradeoffs between fighting and running by comparing two breeds of domestic dog that have experienced strong selection for fighting (pit bulls) and high-speed, economical running (greyhounds). Many of the of the differences that distinguish these two dog breeds are expected to improve running but limit fighting ability in greyhounds, and improve fighting but limit running ability in pit bulls. A number of the skeletal differences observed in greyhounds and pit bulls are also present in the comparison of Australopithecus and early Homo. Aspects of the skeletal anatomy of australopithocines, combined with their relatively high level of sexual dimorphism in body size, raise the possibility that they may have been specialized for male-male aggression. In contrast, Homo exhibits less sexual dimorphism in body size and is characterized by features that are believed to have increased locomotor stamina. These differences between Australopithecus and Homo may be due, in part, to the invention of new weapon technology in the lineage that gave rise to Homo. New weapons may have reduced the conflict between selection for locomotor stamina versus selection for male-male aggression, and allowed a greater independence in the evolution of characters associated with locomotor stamina. In other words, invention of new weapon technology may have opened new avenues for cursorial specialization in Homo.