Predicting the metabolic energy costs of bipedalism using evolutionary robotics

To understand the evolution of bipedalism among the homnoids in an ecological context we need to be able to estimate theenerrgetic cost of locomotion in fossil forms. Ideally such an estimate would be based entirely on morphology since, except for the rare instances where footprints are preserved, this is hte only primary source of evidence available. In this paper we use evolutionary robotics techniques (genetic algoritms, pattern generators and mechanical modeling) to produce a biomimentic simulation of bipedalism based on human body dimensions. The mechnaical simulation is a seven-segment, two-dimensional model with motive force provided by tension generators representing the major muscle groups acting around the lower-limb joints. Metabolic energy costs are calculated from the muscel model, and bipedal gait is generated using a finite-state pattern generator whose parameters are produced using a genetic algorithm with locomotor economy (maximum distance for a fixed energy cost) as the fitness criterion. The model is validated by comparing the values it generates with those for modern humans. The result (maximum efficiency of 200 J m-1) is within 15% of the experimentally derived value, which is very encouraging and suggests that this is a useful analytic technique for investigating the locomotor behaviour of fossil forms. Initial work suggests that in the future this technique could be used to estimate other locomotor parameters such as top speed. In addition, the animations produced by this technique are qualitatively very convincing, which suggests that this may also be a useful technique for visualizing bipedal locomotion.

Anticipatory Accounts

C. Wright Mills called for a truly sociological analysis of actors’ “motive talk,” which decouples the commonsense link between the reasons actors give for their actions and their mental state prior to those actions. Subsequent theoretical and empirical work has focused almost entirely on actors’ retrospective accounting for untoward conduct that has already taken place. The other aspect of Mills’s program, the reasons actors give for potentially untoward future conduct and in particular the empirical investigation of the link between the availability of an acceptable vocabulary of motives for anticipated conduct and the eventual enactment of that conduct, has been largely ignored. This article seeks to rehabilitate these lost dimensions using data from a longitudinal study of mothers’ infant feeding choices and practices. It examines how mothers account, in advance, for the possibility that they may eventually feed their babies in ways they consider suboptimal. Thirty of the thirty-six women interviewed indicated that they intended to breastfeed, emphasizing the benefits of this practice to their babies. However, seventeen of these women also anticipated that they might abandon breastfeeding and presented elaborate accounts of the motives that could lead them to do so. The findings support Mills’s claim that the availability of an acceptable vocabulary of motives for untoward conduct increases the probability that one will engage in such conduct. Mothers who had offered elaborate anticipatory accounts for abandoning breastfeeding were much more likely to do so than those who did not offer such accounts.