The estimation and evolution of hominin body mass

Impact of relative lower-limb length on heat loss and body temperature during running

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.

Footprint evidence for locomotor diversity and shared habitats among early Pleistocene hominins

For much of the Pliocene and Pleistocene, multiple hominin species coexisted in the same regions of eastern and southern Africa. Due to the limitations of the skeletal fossil record, questions regarding their interspecific interactions remain unanswered. We report the discovery of footprints (~1.5 million years old) from Koobi Fora, Kenya, that provide the first evidence of two different patterns of Pleistocene hominin bipedalism appearing on the same footprint surface. New analyses show that this is observed repeatedly across multiple contemporaneous sites in the eastern Turkana Basin. These data indicate a sympatric relationship between Homo erectus and Paranthropus boisei, suggesting that lake margin habitats were important to both species and highlighting the possible influence of varying levels of coexistence, competition, and niche partitioning in human evolution.

Technical note: Prediction of body mass from stature and pelvic breadth

Equations for predicting body mass from stature and bi-iliac (maximum pelvic) breadth have been developed, but have had variable success when applied to living or recently deceased individuals, calling into question their general applicability. Here we test these equations on a large, ethnically diverse sample. Skeletal and anthropometric data for 507 recently deceased Indigenous, Hispanic, and non-Hispanic White adults were obtained from the New Mexico Decedent Image Database. The body mass of individuals with a "normal" body mass index (BMI = 18.5-24.9) is very accurately predicted, with an average directional bias of about 1% and an average random error of less than 8%. Underweight individuals (BMI < 18.5) are overpredicted, while overweight (BMI = 25-29.9) and especially obese (BMI≥30) individuals are underpredicted. Within BMI categories, there is a strong and isometric relationship between predicted and true body mass. Individual body mass prediction errors using the stature/bi-iliac method are mainly dependent on variation in BMI. Because earlier humans were more likely to fall within or close to the normal BMI range, the equations should be applicable, on an individual basis, in archeological and paleontological contexts. Because of the prevalence of obesity in many modern populations, these equations are not applicable in a general forensic context. We derive new equations from nonobese individuals in our sample (n = 338), which produce reasonable average prediction errors. If obese individuals can be identified using other skeletal parameters, these equations may be useful in estimating body mass in nonobese forensic cases.

The effects of the industrial transition on lower limb bone structure: A comparison of the inhabitants of Pecos Pueblo and present-day Indigenous peoples of New Mexico

OBJECTIVES

Comparisons between Indigenous peoples over time and within a particular geographic region can shed light on the impact of environmental transitions on the skeleton, including relative bone strength, sexual dimorphism, and age-related changes. Here we compare long bone structural properties of the inhabitants of the late prehistoric-early historic Pecos Pueblo with those of present-day Indigenous individuals from New Mexico.

MATERIALS AND METHODS

Femora and tibiae of 126 adults from Pecos Pueblo and 226 present-day adults were included in the study. Cross-sectional diaphyseal properties-areas and second moments of area-were obtained from past studies of the Pecos Pueblo skeletal sample, and from computed tomography scans of recently deceased individuals in the present-day sample.

RESULTS

Femora and tibiae from Pecos individuals are stronger relative to body size than those of present-day Indigenous individuals. Present-day individuals are taller but not wider, and this body shape difference affects cross-sectional shape, more strongly proximally. The tibia shows anteroposterior strengthening among Pecos individuals, especially among males. Sexual dimorphism in midshaft bone shape is stronger within the Pecos Pueblo sample. With aging, Pecos individuals show more medullary expansion but also more subperiosteal expansion than present-day individuals, maintaining bone strength despite cortical thinning.

DISCUSSION

Higher activity levels, carried out over rough terrain and throughout adult life, likely explain the relatively stronger lower limb bones of the Pecos individuals, as well as their greater subperiosteal expansion with aging. Greater sexual dimorphism in bone structure among Pecos individuals potentially reflects greater gender-based differences in behavioral patterns.