Abstract
While human sexual dimorphism is generally expected to be the result of differential reproductive strategies, it has the potential to create differences in the energetics of locomotion and the speed at which each morph travels, particularly since people have been shown to choose walking speeds around their metabolic optimum. Here, people of varying sizes walked around a track at four self-selected speeds while their metabolic rate was collected, in order to test whether the size variation within a population could significantly affect the shape of the optimal walking curve. The data show that larger people have significantly faster optimal walking speeds, higher costs at their optimal speed, and a more acute optimal walking curve (thus an increased penalty for walking at suboptimal speeds). Bigger people who also have wider bitrochanteric breadths have lower metabolic costs at their minimum than bigger people with a more narrow bitrochanteric breadth. Finally, tibia length significantly positively predicts optimal walking speed. These results suggest sex-specific walking groups typical of living human populations may be the result of energy maximizing strategies. In addition, testable hypotheses of group strategies are put forth.
Highlights
In recent years a number of key paleoanthropological finds and reconstructions have pushed into the forefront ideas of mobility strategies within and between hominin groups or species
Body size shows a strong relationship with cost of transport (CoT) curves, and larger people have significantly faster optimal walking speeds; this ability to walk at faster speeds is offset by increased curvature around these faster speeds (∼30% more acute)
This means that the energetic penalty to walk at sub-optimal speeds is much increased in larger people—who are already paying absolutely larger costs to walk (∼20% increase in cost)
Summary
In recent years a number of key paleoanthropological finds and reconstructions have pushed into the forefront ideas of mobility strategies within and between hominin groups or species. Changes in mobility have consistently been shown to influence weight loss/weight gain, and ovarian function and fecundity have consistently been shown to be sensitive to changes in the metabolic balance/weight, such that an increased imbalance between energy in and energy out decreases fertility [12,13,14,15,16,17]. The speed of moving across a landscape and the energetic efficiency of mobility must be assessed together in order to understand the selection pressures involved in maintaining reproduction and accessing resources across any series of niche adaptations
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