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Among the costs of reproduction, carrying one's infant incurs one of the greatest drains on maternal energy, simply because of the added mass alone. Because of the dearth of archaeological evidence, however, how early bipeds dealt with the additional cost of having to carry infants who were less able to support their body weight against gravity is not particularly well understood. This article presents evidence on the caloric drain of carrying an infant in one's arms versus having a tool with which to sling the infant and carry her passively. The burden of carrying an infant in one's arms is on average 16% greater than having a tool to support the baby's mass and seems to have the potential to be a greater energetic burden even than lactation. In addition, carrying a baby in one's arms shortens and quickens the stride. An anthropometric trait that seems to offset some of the increased cost of carrying a baby in the arms is a wider bi-trochanteric width. [ABSTRACT FROM AUTHOR]

Objectives: Long lower limbs relative to body size are thought to be an adaptation to prevent excessive increases in body temperature during running in hot climate. The advantage of long lower limbs relative to body size is usually explained by an increase in body surface area relative to mass; however, the influence of limb length on relative body surface area was shown to be minor. We aimed to experimentally test the effect of relative lower-limb length (LLL) on body temperature changes during running. Furthermore, we tested the effect of relative LLL on relative body surface area., Materials and Methods: Adult men (n = 37) ran for 40 min on a treadmill, while their core temperature (ingestible thermometer), skin temperature (infrared thermography), and oxygen consumption (indirect calorimetry) were measured. Relative LLL was calculated as residuals from linear regression of LLL on stature. Linear regression was used to test the effect of relative LLL on standardized heat loss (heat loss/heat production), mean body temperature (weighted mean of skin and core temperatures), and body surface area., Results: Relative LLL had a positive effect on standardized heat loss and a negative effect on mean body temperature change during running. Relative LLL had a positive effect on the proportion of body surface area allocated to the lower limbs but not on the relative body surface area., Discussion: The reduced increase in mean body temperature associated with long lower limbs suggests an advantage of relatively long lower limbs for greater endurance and speed during persistence hunting or contemporary running events., (© 2024 The Author(s). American Journal of Biological Anthropology published by Wiley Periodicals LLC.)

Recent research on the pelvis has clarified the flexibility of pelvic bones to manage nearly infinite possibilities in terms of selection and drift, while still maintaining excellent bipedalism. Despite this work, and the studies outlining the diversity of pelvic morphology across the hominin lineage, conversations continue to be stymied by distractions related to purported trade-offs that the different functions the pelvis must either allow for (e.g., parturition) or directly perform (e.g., attachment sites of muscles). Here we show that tight constraints on morphology are not evident in the pelvic variation of multiple human populations. We thus provide further evidence that human pelves are not geometrically similar and that pelvic morphology successfully balances the intersection of population history, active selective, and drift., (© 2023 The Authors. Evolutionary Anthropology published by Wiley Periodicals LLC.)

The sexual division of labor among human foraging populations has typically been recognized as involving males as hunters and females as gatherers. Recent archeological research has questioned this paradigm with evidence that females hunted (and went to war) throughout the Homo sapiens lineage, though many of these authors assert the pattern of women hunting may only have occurred in the past. The current project gleans data from across the ethnographic literature to investigate the prevalence of women hunting in foraging societies in more recent times. Evidence from the past one hundred years supports archaeological finds from the Holocene that women from a broad range of cultures intentionally hunt for subsistence. These results aim to shift the male-hunter female-gatherer paradigm to account for the significant role females have in hunting, thus dramatically shifting stereotypes of labor, as well as mobility., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Anderson et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

A major portion of humans' activity-based energy expenditure is taken up by locomotion, particularly walking. Walking behaviors have energetic outcomes and as such can be important windows into how populations and groups adjust to different environmental and task constraints. While sex differences in the speed of paired walkers have been established by others, the dynamics of how walkers adjust their speed in more varied groups and in groups containing children remains unexplored. Furthermore, little ecological data exists to illustrate the relationships between walking speed and child-carrying. Here, we aim to determine how culture impacts the effects of group composition and infant-carrying on walking speed. Because the determinants of group dynamics and parental investment are partially cultural, we examine walking behavior in the Northwestern United States and in Central Uganda. Using an observational method, we recorded the speed, load carriage, and group composition of pedestrians in a single naturalistic urban environment within each country. Our data suggest that children are treated fundamentally differently than other loads or the presence of walking partners, and that major speed adjustments are child-dependent. Our data furthermore indicate that Ugandans walk more slowly in groups than when alone, while Americans walk more quickly in groups. Clear distinctions between the groups make large generalizations about walking behavior difficult, and highlight the importance of culturally specific contexts., Competing Interests: The authors declare there are no competing interests.

Background: Gender differences in kinematics during running have been speculated to be a contributing factor to the lower extremity injury rate disparity between men and women. Specifically, increased non-sagittal motion of the pelvis and hip has been implicated; however it is not known if this difference exists under a variety of locomotion conditions. The purpose of this study was to characterize gender differences in gait kinematics and muscle activities as a function of speed and surface incline and to determine if lower extremity anthropometrics contribute to these differences., Methods: Whole body kinematics of 34 healthy volunteers were recorded along with electromyography of muscles on the right lower limb while each subject walked at 1.2, 1.5, and 1.8m/s and ran at 1.8, 2.7, and 3.6m/s with surface inclinations of 0%, 10%, and 15% grade. Joint angles and muscle activities were compared between genders across each speed-incline condition. Pelvis and lower extremity segment lengths were also measured and compared., Findings: Females displayed greater peak hip internal rotation and adduction, as well as gluteus maximus activity for all conditions. Significant interactions (speed-gender, incline-gender) were present for the gluteus medius and vastus lateralis. Hip adduction during walking was moderately correlated to the ratio of bi-trochanteric width to leg length., Interpretation: Our findings indicate females display greater non-sagittal motion. Future studies are needed to better define the relationship of these differences to injury risk.

Numerous studies have discussed the influence of thermoregulation on hominin body shape concluding, in accordance with Allen's rule, that the presence of relatively short limbs on both extant as well as extinct hominin populations offers an advantage for survival in cold climates by reducing the limb's surface area to volume ratio. Moreover, it has been suggested that shortening the distal limb segment compared to the proximal limb segment may play a larger role in thermoregulation due to a greater relative surface area of the shank. If longer limbs result in greater heat dissipation, we should see higher resting metabolic rates (RMR) in longer-limbed individuals when temperature conditions fall, since the resting rate will need to replace the lost heat. We collected resting oxygen consumption on volunteer human subjects to assess the correlation between RMR and lower limb length in human subjects, as well as to reexamine the prediction that shortening the distal segment would have a larger effect on heat loss and, thus, RMR than the shortening of the proximal segment. Total lower limb length exhibits a statistically significant relationship with resting metabolic rate (p<0.001; R(2)=0.794). While this supports the hypothesis that as limb length increases, resting metabolic rate increases, it also appears that thigh length, rather than the length of the shank, drives this relationship. The results of the present study confirm the widely-held expectation of Allen's rule, that short limbs reduce the metabolic cost of maintaining body temperature, while long limbs result in greater heat dissipation regardless of the effect of mass. The present results suggest that the shorter limbs of Neandertals, despite being energetically disadvantageous while walking, would indeed have been advantageous for thermoregulation.