The changes in the anatomy of the pelvis and lower limb observed with the appearance of Homo ergaster probably did not fully offset the increased expenditure resulting from a larger body mass. Moreover, the narrow pelvis in modern humans does not contribute to greater efficiency of locomotion.

Objectives: Load transport activities are of vital importance to current foragers for daily subsistence tasks; thus, it has been suggested that these practices have transformed physical and behavioral characteristics through human evolution.Together with the procurement targets and strategies, the transportation of resources acquired while foraging is strongly influenced by the sex of the foragers. In hunter-gatherer societies, women, despite their smaller body size, usually carry heavier burdens than males. In this study, whether those behavioral differences can be explained by a different economy of load-carriage by sex, irrespective of the body mass of the individuals, is investigated. Material and methods: The energy expenditure of a sample of 48 volunteers (21 females, 27 males) during a set of locomotion and burden transport trials was monitored. Two indexes were computed to compare the increment in the cost of locomotion relative to the load carried by sex. Results: The results demonstrate that both males and females, carrying the same relative loads, experience the same increment over the cost of their unloaded locomotion. Therefore, apart from obvious differences in body mass, there is no evidence of a dissimilar economy favoring one sex over the other that would explain the differences in load-carriage activities observed among current foraging populations.Conclusions: These outcomes provide new conclusions about the constraints of the behavioral ecology of burden transport activities, and highlight the necessity to reevaluate, from an evolutionary perspective, the ideas about the sexual division of subsistence labor in hunter-gatherer and agriculturalist populations.

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Explanations for the brain size increments through primate and, particularly, human evolution are numerous. Commonly, these hypotheses rely on the influence that behavioral and ecological variables have on brain size in extant primates, such as diet quality, social group size, or home range (HR) area. However, HR area does not reflect the time spent moving. As such, it has not been properly addressed whether the effort involved in movement could have affected brain size evolution in primates. This study aimed to test the influence of daily movement on primates’ brain sizes, controlling for these other behavioral and ecological factors. We used a large comparative dataset of extant primate species and phylogenetic comparative methods. Our results show a significant correlation between daily movement and brain mass, which is not explained by the influence of diet, social group size, HR, or body mass. Hence, from an evolutionary timescale, a longer daily movement distance is not a constraining factor for the energetic investment in a larger brain. On the contrary, increased mobility could have contributed to brain mass incrementations through evolution.

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Materials and methods: An experimental study was carried out indoors in a sample of 74 children and adolescents of both sexes, between 7 and 14 years of age. Volunteers walked on a treadmill at six different speeds, and the gross cost of transport (CoT), minimum gross energy cost (minCoT), and optimal locomotion speed (OLS) were determined for each individual. These values were compared with the optimal values for adults, as reported in the literature.Results: Our results show that OLS is similar in boys and girls, and that there are no sex differences in minCoT. Older individuals, as a consequence of their larger size, spend more energy at their optimal speed than younger children.Discussion: Juveniles are not a real burden for the rest of the group in foraging societies, neither in energetic terms nor in locomotor efficiency, being able to achieve optimal walking speeds similar to adults. The so-called energetic dilemma for sexmixed walking groups does not affect juveniles when moving together with adults or in sex-mixed parties.