Department of Anthropology, Hunter College, NYCEP
Saturday Morning, Alexander's
How are hind limb length and locomotor economy related to ranging ecology in hominins and other mammals? It is often proposed that increased ranging leads to selection for improved economy and longer limbs, yet there is little evidence supporting these links among extant mammals. Here, I model the selection pressures acting on limb length and locomotor economy in terrestrial animals, using net energy intake during foraging as a proximate measure of fitness. This simple model indicates that selection for improved economy and increased limb length is highly dependent on foraging efficiency. For species that obtain ten or more calories of food energy for every calorie spent foraging, the selection pressure for improved economy (i.e., lower foraging costs) is very low. Examining daily ranging distances and locomotor costs among 166 extant species suggests that nearly all terrestrial animals, including the great apes, obtain sufficiently high foraging efficiencies that selection for improved locomotor economy is minimal. However, the model suggests that, as early hominins transitioned to habitats or diets with lower foraging return rates, selection for improved economy would have increased dramatically. This may help explain the persistence of poor locomotor economy in apes and the evolution of anatomical features that improve walking economy in australopiths and later hominins, including modern humans.
This work was supported by Hunter College.