Lucy's length: stature reconstruction in Australopithecus afarensis (A.L.288-1) with implications for other small-bodied hominids

A three-dimensional musculoskeletal model of the pelvis and lower limb of Australopithecus afarensis

OBJECTIVES

Musculoskeletal modeling is a powerful approach for studying the biomechanics and energetics of locomotion. Australopithecus (A.) afarensis is among the best represented fossil hominins and provides critical information about the evolution of musculoskeletal design and locomotion in the hominin lineage. Here, we develop and evaluate a three-dimensional (3-D) musculoskeletal model of the pelvis and lower limb of A. afarensis for predicting muscle-tendon moment arms and moment-generating capacities across lower limb joint positions encompassing a range of locomotor behaviors.

MATERIALS AND METHODS

A 3-D musculoskeletal model of an adult A. afarensis pelvis and lower limb was developed based primarily on the A.L. 288-1 partial skeleton. The model includes geometric representations of bones, joints and 35 muscle-tendon units represented using 43 Hill-type muscle models. Two muscle parameter datasets were created from human and chimpanzee sources. 3-D muscle-tendon moment arms and isometric joint moments were predicted over a wide range of joint positions.

RESULTS

Predicted muscle-tendon moment arms generally agreed with skeletal metrics, and corresponded with human and chimpanzee models. Human and chimpanzee-based muscle parameterizations were similar, with some differences in maximum isometric force-producing capabilities. The model is amenable to size scaling from A.L. 288-1 to the larger KSD-VP-1/1, which subsumes a wide range of size variation in A. afarensis.

DISCUSSION

This model represents an important tool for studying the integrated function of the neuromusculoskeletal systems in A. afarensis. It is similar to current human and chimpanzee models in musculoskeletal detail, and will permit direct, comparative 3-D simulation studies.

Beyond Dimorphism: Body Size Variation Among Adult Orangutans Is Not Dichotomous by Sex

Among extant great apes, orangutans are considered the most sexually dimorphic in body size. However, the expression of sexual dimorphism in orangutans is more complex than simply males being larger than females. At sexual maturity, some male orangutans develop cheek pads (flanges), while other males remain unflanged even after becoming reproductively capable. Sometimes flange development is delayed in otherwise sexually mature males for a few years. In other cases, flange development is delayed for many years or decades, with some males even spending their entire lifespan as unflanged adults. Thus, unflanged males of various chronological ages can be mistakenly identified as "subadults." Unflanged adult males are typically described as "female-sized," but this may simply reflect the fact that unflanged male body size has only ever been measured in peri-pubescent individuals. In this study, we measured the skeletons of 111 wild adult orangutans (Pongo spp.), including 20 unflanged males, 45 flanged males, and 46 females, resulting in the largest skeletal sample of unflanged males yet studied. We assessed long bone lengths (as a proxy for stature) for all 111 individuals and recorded weights-at-death, femoral head diameters, bi-iliac breadths, and long bone cross-sectional areas (CSA) (as proxies for mass) for 27 of these individuals, including seven flanged males, three adult confirmed-unflanged males, and three young adult likely-unflanged males. ANOVA and Kruskal-Wallis tests with Tukey and Dunn post-hoc pairwise comparisons, respectively, showed that body sizes for young adult unflanged males are similar to those of the adult females in the sample (all P ≥ 0.09 except bi-iliac breadth), whereas body sizes for adult unflanged males ranged between those of adult flanged males and adult females for several measurements (all P < 0.001). Thus, sexually mature male orangutans exhibit body sizes that range from the female end of the spectrum to the flanged male end of the spectrum. These results exemplify that the term "sexual dimorphism" fails to capture the full range of variation in adult orangutan body size. By including adult unflanged males in analyses of body size and other aspects of morphology, not as aberrations but as an expected part of orangutan variation, we may begin to shift the way that we think about features typically considered dichotomous according to biological sex.

The taxonomic attribution of African hominin postcrania from the Miocene through the Pleistocene: Associations and assumptions

Postcranial bones may provide valuable information about fossil taxa relating to their locomotor habits, manipulative abilities and body sizes. Distinctive features of the postcranial skeleton are sometimes noted in species diagnoses. Although numerous isolated postcranial fossils have become accepted by many workers as belonging to a particular species, it is worthwhile revisiting the evidence for each attribution before including them in comparative samples in relation to the descriptions of new fossils, functional analyses in relation to particular taxa, or in evolutionary contexts. Although some workers eschew the taxonomic attribution of postcranial fossils as being less important (or interesting) than interpreting their functional morphology, it is impossible to consider the evolution of functional anatomy in a taxonomic and phylogenetic vacuum. There are 21 widely recognized hominin taxa that have been described from sites in Africa dated from the Late Miocene to the Middle Pleistocene; postcranial elements have been attributed to 17 of these. The bones that have been thus assigned range from many parts of a skeleton to isolated elements. However, the extent to which postcranial material can be reliably attributed to a specific taxon varies considerably from site to site and species to species, and is often the subject of considerable debate. Here, we review the postcranial remains attributed to African hominin taxa from the Late Miocene to the Middle and Late Pleistocene and place these assignations into categories of reliability. The catalog of attributions presented here may serve as a guide for making taxonomic decisions in the future.

Using BayesModelS to provide Bayesian- and phylogenetically-informed primate body mass predictions

An accurate prediction of the body mass of an extinct species can greatly inform the reconstruction of that species' ecology. Therefore, paleontologists frequently predict the body mass of extinct taxa from fossilized materials, particularly dental dimensions. Body mass prediction has traditionally been performed in a frequentist statistical framework, and accounting for phylogenetic relationships while calibrating prediction models has only recently become more commonplace. In this article, we apply BayesModelS-a phylogenetically informed Bayesian prediction method-to predict body mass in a sample of 49 euarchontan species (24 strepsirrhines, 20 platyrrhines, 3 tarsiids, 1 dermopteran, and 1 scandentian) and compare this approach's body mass prediction accuracy with other commonly used techniques, namely ordinary least squares, phylogenetic generalized least squares, and phylogenetic independent contrasts (PICs). When predicting the body masses of extant euarchontans from dental and postcranial variables, BayesModelS and PICs have substantially higher predictive accuracy than ordinary least squares and phylogenetic generalized least squares. The improved performances of BayesModelS and PIC are most evident for dentally derived body mass proxies or when body mass proxies have high degrees of phylogenetic covariance. Predicted values generated by BayesModelS and PIC methods also show less variance across body mass proxies when applied to the Eocene adapiform Notharctus tenebrosus. These more explicitly phylogenetically based methods should prove useful for predicting body mass in a paleontological context, and we provide executive scripts for both BayesModelS and PIC to increase ease of application.

Allometric scaling and growth: Evaluation and applications in subadult body mass estimation

OBJECTIVES

Previously developed methods in subadult body mass estimation have not been tested in populations other than European-American or African-American. This study uses a contemporary Taiwanese sample to test these methods. Through evaluating their accuracy and bias, we addressed whether the allometric relationships between body mass and skeletal traits commonly used in subadult body mass estimation are conserved among different populations.

MATERIALS AND METHODS

Computed tomography scans of lower limbs from individuals aged 0-17 years old of both sexes were collected from National Taiwan University Hospital along with documented body weight. Polar second moment of area, distal femoral metaphyseal breadth, and maximum superior/inferior femoral head diameter were collected either directly from the scans or from reconstructed 3D models. Estimated body mass was compared with documented body mass to assess the performance of the equations.

RESULTS

Current methods provided good body mass estimates in Taiwanese individuals, with accuracy and bias similar to those reported in other validation studies. A tendency for increasing error with increasing age was observed for all methods. Reduced major axis regression showed the allometric relationships between different skeletal traits and body mass across different age categories can all be summarized using a common fitted line. A revised, maximum likelihood-based approach was proposed for all skeletal traits.

DISCUSSION

The results suggested that the allometric relationships between body mass and different skeletal traits are largely conserved among populations. The revised method provided improved applicability with strong underlying theoretical justifications, and potential for future improvements.

Body mass estimation from footprint size in hominins

Although many studies relating stature to foot length have been carried out, the relationship between foot size and body mass remains poorly understood. Here we investigate this relationship in 193 adult and 50 juvenile habitually unshod/minimally shod individuals from five different populations-Machiguenga, Daasanach, Pumé, Hadzabe, and Samoans-varying greatly in body size and shape. Body mass is highly correlated with foot size, and can be predicted from foot area (maximum length × breadth) in the combined sample with an average error of about 10%. However, comparisons among populations indicate that body shape, as represented by the body mass index (BMI), has a significant effect on foot size proportions, with higher BMI samples exhibiting relatively smaller feet. Thus, we also derive equations for estimating body mass from both foot size and BMI, with BMI in footprint samples taken as an average value for a taxon or population, estimated independently from skeletal remains. Techniques are also developed for estimating body mass in juveniles, who have relatively larger feet than adults, and for converting between foot and footprint size. Sample applications are given for five Pliocene through Holocene hominin footprint samples from Laetoli (Australopithecus afarensis), Ileret (probable Homo erectus), Happisburgh (possible Homo antecessor), Le Rozel (archaic Homo sapiens), and Barcin Höyük (H. sapiens). Body mass estimates for Homo footprint samples appear reasonable when compared to skeletal estimates for related samples. However, estimates for the Laetoli footprint sample using the new formulae appear to be too high when compared to skeletal estimates for A. afarensis. Based on the proportions of A.L. 288-1, this is apparently a result of relatively large feet in this taxon. A different method using a ratio between body mass and foot area in A.L. 288-1 provides estimates more concordant with skeletal estimates and should be used for A. afarensis.

Regression equations for the estimation of stature and body mass using a Greek documented skeletal collection

Body size is an important variable in bioarchaeological and forensic studies, making the accurate calculation of stature and body mass imperative. Given that anatomical and morphometric approaches offer accurate results but require a particularly good preservation of the skeletal material, whereas mathematical and mechanical methods are more easily applicable but they are largely population-specific, the present paper uses a 'hybrid' approach in order to generate regression equations for the prediction of stature and body mass in a modern Greek sample. Specifically, anatomical and morphometric methods were used to calculate the stature and body mass of the individuals and regression equations using the Ordinary Least Squares and Reduced Major Axis methods were generated with long bone lengths and femoral head breadth as predictors. The obtained equations exhibit low random and directional error and perform better than existing equations designed using different samples from the United States, Europe, and the Balkans. Therefore, these equations are more appropriate for modern Greek material.

The evolution of body size and shape in the human career

Body size is a fundamental biological property of organisms, and documenting body size variation in hominin evolution is an important goal of palaeoanthropology. Estimating body mass appears deceptively simple but is laden with theoretical and pragmatic assumptions about best predictors and the most appropriate reference samples. Modern human training samples with known masses are arguably the 'best' for estimating size in early bipedal hominins such as the australopiths and all members of the genus Homo, but it is not clear if they are the most appropriate priors for reconstructing the size of the earliest putative hominins such as Orrorin and Ardipithecus The trajectory of body size evolution in the early part of the human career is reviewed here and found to be complex and nonlinear. Australopith body size varies enormously across both space and time. The pre-erectus early Homo fossil record from Africa is poor and dominated by relatively small-bodied individuals, implying that the emergence of the genus Homo is probably not linked to an increase in body size or unprecedented increases in size variation. Body size differences alone cannot explain the observed variation in hominin body shape, especially when examined in the context of small fossil hominins and pygmy modern humans.This article is part of the themed issue 'Major transitions in human evolution'.

The role of plantigrady and heel-strike in the mechanics and energetics of human walking with implications for the evolution of the human foot

Human bipedal locomotion is characterized by a habitual heel-strike (HS) plantigrade gait, yet the significance of walking foot-posture is not well understood. To date, researchers have not fully investigated the costs of non-heel-strike (NHS) walking. Therefore, we examined walking speed, walk-to-run transition speed, estimated locomotor costs (lower limb muscle volume activated during walking), impact transient (rapid increase in ground force at touchdown) and effective limb length (ELL) in subjects (n=14) who walked at self-selected speeds using HS and NHS gaits. HS walking increases ELL compared with NHS walking since the center of pressure translates anteriorly from heel touchdown to toe-off. NHS gaits led to decreased absolute walking speeds (P=0.012) and walk-to-run transition speeds (P=0.0025), and increased estimated locomotor energy costs (P<0.0001) compared with HS gaits. These differences lost significance after using the dynamic similarity hypothesis to account for the effects of foot landing posture on ELL. Thus, reduced locomotor costs and increased maximum walking speeds in HS gaits are linked to the increased ELL compared with NHS gaits. However, HS walking significantly increases impact transient values at all speeds (P<0.0001). These trade-offs may be key to understanding the functional benefits of HS walking. Given the current debate over the locomotor mechanics of early hominins and the range of foot landing postures used by nonhuman apes, we suggest the consistent use of HS gaits provides key locomotor advantages to striding bipeds and may have appeared early in hominin evolution.

A Critical Evaluation of the Down Syndrome Diagnosis for LB1, Type Specimen of Homo floresiensis

The Liang Bua hominins from Flores, Indonesia, have been the subject of intense scrutiny and debate since their initial description and classification in 2004. These remains have been assigned to a new species, Homo floresiensis, with the partial skeleton LB1 as the type specimen. The Liang Bua hominins are notable for their short stature, small endocranial volume, and many features that appear phylogenetically primitive relative to modern humans, despite their late Pleistocene age. Recently, some workers suggested that the remains represent members of a small-bodied island population of modern Austro-Melanesian humans, with LB1 exhibiting clinical signs of Down syndrome. Many classic Down syndrome signs are soft tissue features that could not be assessed in skeletal remains. Moreover, a definitive diagnosis of Down syndrome can only be made by genetic analysis as the phenotypes associated with Down syndrome are variable. Most features that contribute to the Down syndrome phenotype are not restricted to Down syndrome but are seen in other chromosomal disorders and in the general population. Nevertheless, we re-evaluated the presence of those phenotypic features used to support this classification by comparing LB1 to samples of modern humans diagnosed with Down syndrome and euploid modern humans using comparative morphometric analyses. We present new data regarding neurocranial, brain, and symphyseal shape in Down syndrome, additional estimates of stature for LB1, and analyses of inter- and intralimb proportions. The presence of cranial sinuses is addressed using CT images of LB1. We found minimal congruence between the LB1 phenotype and clinical descriptions of Down syndrome. We present important differences between the phenotypes of LB1 and individuals with Down syndrome, and quantitative data that characterize LB1 as an outlier compared with Down syndrome and non-Down syndrome groups. Homo floresiensis remains a phenotypically unique, valid species with its roots in Plio-Pleistocene Homo taxa.

Architecture and functional ecology of the human gastrocnemius muscle-tendon unit

The gastrocnemius muscle-tendon unit (MTU) is central to human locomotion. Structural variation in the human gastrocnemius MTU is predicted to affect the efficiency of locomotion, a concept most often explored in the context of performance activities. For example, stiffness of the Achilles tendon varies among individuals with different histories of competitive running. Such a finding highlights the functional variation of individuals and raises the possibility of similar variation between populations, perhaps in response to specific ecological or environmental demands. Researchers often assume minimal variation in human populations, or that industrialized populations represent the human species as well as any other. Yet rainforest hunter-gatherers, which often express the human pygmy phenotype, contradict such assumptions. Indeed, the human pygmy phenotype is a potential model system for exploring the range of ecomorphological variation in the architecture of human hindlimb muscles, a concept we review here.

Body mass estimates of hominin fossils and the evolution of human body size

Body size directly influences an animal's place in the natural world, including its energy requirements, home range size, relative brain size, locomotion, diet, life history, and behavior. Thus, an understanding of the biology of extinct organisms, including species in our own lineage, requires accurate estimates of body size. Since the last major review of hominin body size based on postcranial morphology over 20 years ago, new fossils have been discovered, species attributions have been clarified, and methods improved. Here, we present the most comprehensive and thoroughly vetted set of individual fossil hominin body mass predictions to date, and estimation equations based on a large (n = 220) sample of modern humans of known body masses. We also present species averages based exclusively on fossils with reliable taxonomic attributions, estimates of species averages by sex, and a metric for levels of sexual dimorphism. Finally, we identify individual traits that appear to be the most reliable for mass estimation for each fossil species, for use when only one measurement is available for a fossil. Our results show that many early hominins were generally smaller-bodied than previously thought, an outcome likely due to larger estimates in previous studies resulting from the use of large-bodied modern human reference samples. Current evidence indicates that modern human-like large size first appeared by at least 3-3.5 Ma in some Australopithecus afarensis individuals. Our results challenge an evolutionary model arguing that body size increased from Australopithecus to early Homo. Instead, we show that there is no reliable evidence that the body size of non-erectus early Homo differed from that of australopiths, and confirm that Homo erectus evolved larger average body size than earlier hominins.

Spatial and temporal variation of body size among early Homo

The estimation of body size among the earliest members of the genus Homo (2.4-1.5Myr [millions of years ago]) is central to interpretations of their biology. It is widely accepted that Homo ergaster possessed increased body size compared with Homo habilis and Homo rudolfensis, and that this may have been a factor involved with the dispersal of Homo out of Africa. The study of taxonomic differences in body size, however, is problematic. Postcranial remains are rarely associated with craniodental fossils, and taxonomic attributions frequently rest upon the size of skeletal elements. Previous body size estimates have been based upon well-preserved specimens with a more reliable species assessment. Since these samples are small (n < 5) and disparate in space and time, little is known about geographical and chronological variation in body size within early Homo. We investigate temporal and spatial variation in body size among fossils of early Homo using a 'taxon-free' approach, considering evidence for size variation from isolated and fragmentary postcranial remains (n = 39). To render the size of disparate fossil elements comparable, we derived new regression equations for common parameters of body size from a globally representative sample of hunter-gatherers and applied them to available postcranial measurements from the fossils. The results demonstrate chronological and spatial variation but no simple temporal or geographical trends for the evolution of body size among early Homo. Pronounced body size increases within Africa take place only after hominin populations were established at Dmanisi, suggesting that migrations into Eurasia were not contingent on larger body sizes. The primary evidence for these marked changes among early Homo is based upon material from Koobi Fora after 1.7Myr, indicating regional size variation. The significant body size differences between specimens from Koobi Fora and Olduvai support the cranial evidence for at least two co-existing morphotypes in the Early Pleistocene of eastern Africa.

Human footprint variation while performing load bearing tasks

Human footprint fossils have provided essential evidence about the evolution of human bipedalism as well as the social dynamics of the footprint makers, including estimates of speed, sex and group composition. Generally such estimates are made by comparing footprint evidence with modern controls; however, previous studies have not accounted for the variation in footprint dimensions coming from load bearing activities. It is likely that a portion of the hominins who created these fossil footprints were carrying a significant load, such as offspring or foraging loads, which caused variation in the footprint which could extend to variation in any estimations concerning the footprint’s maker. To identify significant variation in footprints due to load-bearing tasks, we had participants (N = 30, 15 males and 15 females) walk at a series of speeds carrying a 20kg pack on their back, side and front. Paint was applied to the bare feet of each participant to create footprints that were compared in terms of foot length, foot width and foot area. Female foot length and width increased during multiple loaded conditions. An appreciation of footprint variability associated with carrying loads adds an additional layer to our understanding of the behavior and morphology of extinct hominin populations.

Stature estimation in ancient Egyptians: a new technique based on anatomical reconstruction of stature

Trotter and Gleser's (Trotter and Gleser: Am J Phys Anthropol 10 (1952) 469-514; Trotter and Gleser: Am J Phys Anthropol 16 (1958) 79-123) long bone formulae for US Blacks or derivations thereof (Robins and Shute: Hum Evol 1 (1986) 313-324) have been previously used to estimate the stature of ancient Egyptians. However, limb length to stature proportions differ between human populations; consequently, the most accurate mathematical stature estimates will be obtained when the population being examined is as similar as possible in proportions to the population used to create the equations. The purpose of this study was to create new stature regression formulae based on direct reconstructions of stature in ancient Egyptians and assess their accuracy in comparison to other stature estimation methods. We also compare Egyptian body proportions to those of modern American Blacks and Whites. Living stature estimates were derived using a revised Fully anatomical method (Raxter et al.: Am J Phys Anthropol 130 (2006) 374-384). Long bone stature regression equations were then derived for each sex. Our results confirm that, although ancient Egyptians are closer in body proportion to modern American Blacks than they are to American Whites, proportions in Blacks and Egyptians are not identical. The newly generated Egyptian-based stature regression formulae have standard errors of estimate of 1.9-4.2 cm. All mean directional differences are less than 0.4% compared to anatomically estimated stature, while results using previous formulae are more variable, with mean directional biases varying between 0.2% and 1.1%, tibial and radial estimates being the most biased. There is no evidence for significant variation in proportions among temporal or social groupings; thus, the new formulae may be broadly applicable to ancient Egyptian remains.

Revision of the Fully technique for estimating statures

The "anatomical" method of Fully (1956 Ann. Legale Med. 35:266-273) for reconstructing stature, involving the addition of skeletal elements from the calcaneus to the skull, has been increasingly used in anthropological and forensic contexts, but has undergone little systematic testing on samples other than the original sample used to develop the technique. The original description by Fully of the method also does not provide completely explicit directions for taking all of the necessary measurements. This study tested the accuracy and applicability of his method, and clarified measurement procedures. The study sample consisted of 119 adult black and white males and females of known cadaveric statures from the Terry Collection. Cadaveric statures were adjusted to living statures, following the recommendations of Trotter and Gleser (1952 Am. J. Phys. Anthropol. 10:469-514). We obtained the best results using maximum vertebral body heights (anterior to the pedicles) and measurement of the articulated talus and calcaneus height in anatomical position. Statures derived using the original Fully technique are strongly correlated with living statures in our sample (r = 0.96), but underestimate living stature by an average of about 2.4 cm. Anatomical considerations also suggest that the correction factors applied by Fully to convert summed skeletal height to living stature are too small. New formulae are derived to calculate living stature from skeletal height. There is no effect of sex or ancestry on stature prediction. Resulting stature estimates are accurate to within 4.5 cm in 95% of the individuals in our sample, with no directional bias.

The short legs of great apes: evidence for aggressive behavior in australopiths

Early hominins, australopiths, were similar to most large primates in having relatively short hindlimbs for their body size. The short legs of large primates are thought to represent specialization for vertical climbing and quadrupedal stability on branches. Although this may be true, there are reasons to suspect that the evolution of short legs may also represent specialization for physical aggression. Fighting in apes is a behavior in which short legs are expected to improve performance by lowering the center of mass during bipedal stance and by increasing the leverage through which muscle forces can be applied to the ground. Among anthropoid primates, body size sexual dimorphism (SSD) and canine height sexual dimorphism (CSD) are strongly correlated with levels of male-male competition, allowing SSD and CSD to be used as indices of male-male aggression. Here I show that the evolution of hindlimb length in apes is inversely correlated with the evolution of SSD (R(2)= 0.683, P-value = 0.006) and the evolution of CSD (R(2)= 0.630, P-value = 0.013). In contrast, a significant correlation was not observed for the relationship between the evolution of hindlimb and forelimb lengths. These observations are consistent with the suggestion that selection for fighting performance has maintained relatively short hindlimbs in species of Hominoidea with high levels of male-male competition. Although australopiths were highly derived for striding bipedalism when traveling on the ground, they retained short legs compared to those of Homo for over two million years, approximately 100,000 generations. Their short legs may be indicative of persistent selection for high levels of aggression.

Body size prediction from juvenile skeletal remains

There are currently no methods for predicting body mass from juvenile skeletal remains and only a very limited number for predicting stature. In this study, stature and body mass prediction equations are generated for each year from 1 to 17 years of age using a subset of the Denver Growth Study sample, followed longitudinally (n = 20 individuals, 340 observations). Radiographic measurements of femoral distal metaphyseal and head breadth are used to predict body mass and long bone lengths are used to predict stature. In addition, pelvic bi-iliac breadth and long bone lengths are used to predict body mass in older adolescents. Relative prediction errors are equal to or smaller than those associated with similar adult estimation formulae. Body proportions change continuously throughout growth, necessitating age-specific formulae. Adult formulae overestimate stature and body mass in younger juveniles, but work well in 17-year-olds from the sample, indicating that in terms of body proportions they are representative of the general population. To illustrate use of the techniques, they are applied to the juvenile Homo erectus (ergaster) KNM-WT 15000 skeleton. New body mass and stature estimates for this specimen are similar to previous estimates derived using other methods. Body mass estimates range from 50 to 53 kg, and stature was probably slightly under 157 cm, although a precise stature estimate is difficult to determine due to differences in linear body proportions between KNM-WT 15000 and the Denver reference sample.

Femur length, body mass, and stature estimates of Orrorin tugenensis, a 6 Ma hominid from Kenya

To understand the palaeobiology of extinct hominids it is useful to estimate their body mass and stature. Although many species of early hominid are poorly preserved, it is occasionally possible to calculate these characteristics by comparison with different extant groups, by use of regression analysis. Calculated body masses and stature determined using these models can then be compared. This approach has been applied to 6 Ma hominid femoral remains from the Tugen Hills, Kenya, attributed to Orrorin tugenensis. It is suggested that the best-preserved young adult individual probably weighed approximately 35-50 kg. Another fragmentary femur results in larger estimates of body mass, indicative of individual variation. The length of the femur of the young adult individual was estimated, by using anthropoid-based regression, to be a minimum of 298 mm. Because whole-femur proportions for Orrorin are unknown, this prediction is conservative and should be revised when additional specimens become available. When this predicted value was used for regression analysis of bonobos and humans it was estimated to be 1.1-1.2 m tall. This value should, however, be viewed as a lower limit.

Flores hominid: New species or microcephalic dwarf?

The proposed new hominid "Homo floresiensis" is based on specimens from cave deposits on the Indonesian island Flores. The primary evidence, dated at approximately 18,000 y, is a skull and partial skeleton of a very small but dentally adult individual (LB1). Incomplete specimens are attributed to eight additional individuals. Stone tools at the site are also attributed to H. floresiensis. The discoverers interpreted H. floresiensis as an insular dwarf derived from Homo erectus, but others see LB1 as a small-bodied microcephalic Homo sapiens. Study of virtual endocasts, including LB1 and a European microcephalic, purportedly excluded microcephaly, but reconsideration reveals several problems. The cranial capacity of LB1 ( approximately 400 cc) is smaller than in any other known hominid < 3.5 Ma and is far too small to derive from Homo erectus by normal dwarfing. By contrast, some associated tools were generated with a prepared-core technique previously unknown for H. erectus, including bladelets otherwise associated exclusively with H. sapiens. The single European microcephalic skull used in comparing virtual endocasts was particularly unsuitable. The specimen was a cast, not the original skull (traced to Stuttgart), from a 10-year-old child with massive pathology. Moreover, the calotte does not fit well with the rest of the cast, probably being a later addition of unknown history. Consideration of various forms of human microcephaly and of two adult specimens indicates that LB1 could well be a microcephalic Homo sapiens. This is the most likely explanation for the incongruous association of a small-brained recent hominid with advanced stone tools.

Patterns of size sexual dimorphism in Australopithecus afarensis: Another look

Size sexual dimorphism is one of the major components of morphological variation and has been associated with socio-ecology and behavioral variables such as mating patterns. Although several studies have addressed the magnitude and pattern of sexual dimorphism in Australopithecus afarensis, one of the earliest hominids, consensus has yet to be reached. This paper uses assigned re-sampling method, a data re-sampling method to estimate the magnitude of sexual dimorphism without relying on individual sex assessments, to examine the fossil hominid sample from Hadar. Two questions are asked: first, whether sexual dimorphism in a selected sample of skeletal elements of A. afarensis is the same as that in living humans, chimpanzees, or gorillas; and second, whether different skeletal elements reflect variation in sexual dimorphism in the same way. All possible metric variables were used as data in applying the method, including seven variables from three elements (mandibular canine, humerus, femur). Analyses show that A. afarensis is similar in size sexual dimorphism to gorillas in femoral variables, to humans in humeral variables, and to chimpanzees in canine variables. The results of this study are compatible with the hypothesis that the pattern of sexual dimorphism in A. afarensis is different from any that are observed in living humans or apes.

Neuromusculoskeletal computer modeling and simulation of upright, straight-legged, bipedal locomotion of Australopithecus afarensis (A.L. 288-1)

The skeleton of Australopithecus afarensis (A.L. 288-1, better known as "Lucy") is by far the most complete record of locomotor morphology of early hominids currently available. Even though researchers agree that the postcranial skeleton of Lucy shows morphological features indicative of bipedality, only a few studies have investigated Lucy's bipedal locomotion itself. Lucy's energy expenditure during locomotion has been the topic of much speculation, but has not been investigated, except for several estimates derived from experimental data collected on other animals. To gain further insights into how Lucy may have walked, we generated a full three-dimensional (3D) reconstruction and forward-dynamic simulation of upright bipedal locomotion of this ancient human ancestor. Laser-scanned 3D bone geometries were combined with state-of-the-art neuromusculoskeletal modeling and simulation techniques from computational biomechanics. A detailed full 3D neuromusculoskeletal model was developed that encompassed all major bones, joints (10), and muscles (52) of the lower extremity. A model of muscle force and heat production was used to actuate the musculoskeletal system, and to estimate total energy expenditure during locomotion. Neural activation profiles for each of the 52 muscles that produced a single step of locomotion, while at the same time minimizing the energy consumed per meter traveled, were searched through numerical optimization. The numerical optimization resulted in smooth locomotor kinematics, and the predicted energy expenditure was appropriate for upright bipedal walking in an individual of Lucy's body size.

A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia

Currently, it is widely accepted that only one hominin genus, Homo, was present in Pleistocene Asia, represented by two species, Homo erectus and Homo sapiens. Both species are characterized by greater brain size, increased body height and smaller teeth relative to Pliocene Australopithecus in Africa. Here we report the discovery, from the Late Pleistocene of Flores, Indonesia, of an adult hominin with stature and endocranial volume approximating 1 m and 380 cm3, respectively--equal to the smallest-known australopithecines. The combination of primitive and derived features assigns this hominin to a new species, Homo floresiensis. The most likely explanation for its existence on Flores is long-term isolation, with subsequent endemic dwarfing, of an ancestral H. erectus population. Importantly, H. floresiensis shows that the genus Homo is morphologically more varied and flexible in its adaptive responses than previously thought.

The role of load-carrying in the evolution of modern body proportions

The first unquestionably bipedal early human ancestors, the species Australopithecus afarensis, were markedly different to ourselves in body proportions, having a long trunk and short legs. Some have argued that 'chimpanzee-like' features such as these suggest a 'bent-hip, bent-knee' (BHBK) posture would have been adopted during gait. Computer modelling studies, however, indicate that this early human ancestor could have walked in a reasonably efficient upright posture, whereas BHBK posture would have nearly doubled the mechanical energy cost of locomotion, as it does the physiological cost of locomotion in ourselves. More modern body proportions first appear at around 1.8-1.5 Ma, with Homo ergaster (early African Homo erectus), represented by the Nariokotome skeleton KNM-WT 15000, in which the legs were considerably longer in relation to the trunk than they are in human adults, although this skeleton represents an adolescent. Several authors have suggested that this morphology would have allowed faster, more endurant walking. But during the same period, the archaeological record indicates a sharp rise in distances over which stone tools or raw materials are transported. Is this coincidental, or can load-carrying also be implicated in selection for a more modern morphology? Computer simulations of loaded walking, verified against kinetic data for humans, show that BHBK gait is even more ineffective while load-carrying. However, walking erect, the Nariokotome individual could have carried loads of 10-15% body mass for less cost, relative to body size, than AL 288-1 walking erect but unloaded. In fact, to the extent that our sample of humans is typical, KNM-WT 15000 would have had better mechanical effectiveness in bearing light loads on the back than modern human adults. Thus, selection for effectiveness in load-carrying, as well as in endurant walking, is indeed likely to have been implicated in the evolution of modern body proportions.

Body proportions of Homo habilis reviewed

The ratio of fore- to hindlimb size plays an important role in our understanding of human evolution. Although Homo habilis was relatively modern craniodentally, its body proportions are commonly believed to have been more apelike than in the earlier Australopithecus afarensis. The evidence for this, however, rests, on two fragmentary skeletons, OH 62 and KNM-ER 3735. The upper limb of the better-preserved OH 62 from Olduvai Gorge is long and slender, but its hindlimb is represented mainly by the proximal portion of a thin femur of uncertain length. The present analysis shows that upper-to-lower limb shaft proportions of both OH 62 and AL 288-1 (A. afarensis) fall in the modern human range of variation, although OH 62 also falls inside that of chimpanzees due to their overlap in small individuals. Despite being more fragmentary, the larger-bodied KNM-ER 3735 lies outside the chimpanzee range and close to the human mean. Because the differences between any of the three individuals are compatible with the range of variation seen in extant hominoid groups, it is not legitimate to infer more primitive upper-to-lower limb shaft proportions for either H. habilis or A. afarensis. Femur length of OH 62 can only be estimated by comparison. Its closest match in size and morphology is with the gracile OH 34 specimen, which therefore provides a better analogue for the reconstruction of OH 62 than the stocky AL 288-1 femur that is traditionally used. OH 34's slender proportions are hardly due to abrasion, but match those of a modern human of that body-size, suggesting that the relative length of OH 62's leg may have been human-like. Brachial proportions, however, remained primitive. Long legs may imply long distance terrestrial travel. Perhaps this adaptation evolved early in the genus Homo, with H. habilis providing an early representative of this important change.

Size and power required for motion with implication for the evolution of early hominids

The fossil record of early hominids (early human ancestors) suggests that their stature and weight had a tendency to increase, but their robusticity (the proportion of radius to length) to decrease. Using a simple musculo-skeletal model, this paper explores possible relationships between size, power required for motion (PRM) and cycle-time, deriving relationships which indicate that PRM per unit of mass and velocity is proportional to robusticity, but inversely proportional to stature. The results derived appear to be in general agreement with published data from physiological experiments. If the material properties of early hominids were similar to those of modern humans and the achievement of minimum PRM was the selective criterion, human stature might tend to increase slightly in human evolution (and, if selective pressures are not removed, might do so in the future but at lower rate). If mobility and stability under loading are the selective criteria, however, human size should not substantially increase in the future.

Estimation of body size and physique from hominin skeletal remains

Three methods of measuring stature from skeletal remains are reviewed: the reconstructed skeletal length, the correspondence of long bone length to stature and the regression of stature on long bone length. Each involves problems and difficulties. For the anthropologist, there is the additional problem of applying findings from extant taxa to extinct taxa with potentially different morphologies and limb proportions. Of the various studies involving regression of the stature the findings of Trotter and Gleser are judged the most robust and useful notwithstanding problems and limitations. The lumbar vertebrae are potentially important as stature predictors. Estimation of body mass from the skeleton is also beset with problems. Eight methods are reviewed: Hartwig-Scherer's taxon independent solution, four methods involving measurements from the weight-bearing appendicular skeleton, Ruff's method using the length of the reconstructed skeleton and an estimate of body breadth, estimates from the total skeletal mass and estimates from the body mass index when the stature is known approximately. Lumbar vertebrae provide reasonable estimates of both body mass and stature and thus by derivation the body mass index. At present both forensic scientists and anthropologists lack adequate data and methods to estimate body size and shape from hominin skeletons. A further large and well-designed study using magnetic resonance imaging is required.

Variation in Human Body Size and Shape

▪ Abstract  Evolutionary trends in human body form provide important context for interpreting variation among modern populations. Average body mass in living humans is smaller than it was during most of the Pleistocene, possibly owing to technological improvements during the past 50,000 years that no longer favored large body size. Sexual dimorphism in body size reached modern levels at least 150,000 years ago and probably earlier. Geographic variation in both body size and shape in earlier humans paralleled latitudinal clines observed today. Climatic adaptation is the most likely primary cause for these gradients, overlain in more recent populations by nutritional effects on growth. Thus, to distinguish growth disturbances, it is necessary to partition out the (presumably genetic) long-term differences in body form between populations that have resulted from climatic selection. An example is given from a study of Inupiat children, using a new index of body shape to assess relative body mass.

Modeling three-dimensional sculptures of australopithecines (Australopithecus afarensis) for the Museum of Natural History of Vienna (Austria): the post-cranial hypothesis

In March 1999, E. Daynes, a sculptor specializing in fossil hominid reconstruction, asked C. Berge to take over the scientific supervision of the reconstruction of two australopithecine post-crania. The heads had been modeled from two skulls found in Hadar (AL 444-2, AL 417). The sculptures were to be represented in a walking stance. The female proportions (AL 417) are estimated from the skeleton of 'Lucy' (AL 288), and the male proportions (AL 444-2) extrapolated from the female ones. Biomechanical and anatomical data (comparison with great apes and humans) are used to reconstruct both dynamic equilibrium and muscular systems. The reconstruction suggests that the fossils moved the pelvis and shoulders extensively when they walked. The hindlimb muscles (such as adductors, gluteal muscles and calf) are fleshy and not or very little tendinous. As indicated by the Laetoli step prints (belonging to a close and contemporaneous species), the foot is adducted during the walk and the support is internal just before take off. In spite of inevitable approximations, such a reconstruction appears to be particularly helpful to bring out morphological and functional traits of the first hominids which are both close to and different from modern humans.

Human evolution: taxonomy and paleobiology

This review begins by setting out the context and the scope of human evolution. Several classes of evidence, morphological, molecular, and genetic, support a particularly close relationship between modern humans and the species within the genus Pan, the chimpanzee. Thus human evolution is the study of the lineage, or clade, comprising species more closely related to modern humans than to chimpanzees. Its stem species is the so-called 'common hominin ancestor', and its only extant member is Homo sapiens. This clade contains all the species more closely-related to modern humans than to any other living primate. Until recently, these species were all subsumed into a family, Hominidae, but this group is now more usually recognised as a tribe, the Hominini. The rest of the review sets out the formal nomenclature, history of discovery, and information about the characteristic morphology, and its behavioural implications, of the species presently included in the human clade. The taxa are considered within their assigned genera, beginning with the most primitive and finishing with Homo. Within genera, species are presented in order of geological age. The entries conclude with a list of the more important items of fossil evidence, and a summary of relevant taxonomic issues.

Estimating stature in fossil hominids: which regression model and reference sample to use?

coResearchers have long appreciated the significant relationship between body size and an animal's overall adaptive strategy and life history. However, much more emphasis has been placed on interpreting body size than on the actual calculation of it. One measure of size that is especially important for human evolutionary studies is stature. Despite a long history of investigation, stature estimation remains plagued by two methodological problems: (1) the choice of the statistical estimator, and (2) the choice of the reference population from which to derive the parameters. This work addresses both of these problems in estimating stature for fossil hominids, with special reference to A.L. 288-1 (Australopithecus afarensis) and WT 15000 (Homo erectus). Three reference samples of known stature with maximum humerus and femur lengths are used in this study: a large (n=2209) human sample from North America, a smaller sample of modern human pygmies (n=19) from Africa, and a sample of wild-collected African great apes (n=85). Five regression techniques are used to estimate stature in the fossil hominids using both univariate and multivariate parameters derived from the reference samples: classical calibration, inverse calibration, major axis, reduced major axis and the zero-intercept ratio model. We also explore a new diagnostic to test extrapolation and allometric differences with multivariate data, and we calculate 95% confidence intervals to examine the range of variation in estimates for A.L. 288-1, WT 15000 and the new Bouri hominid (contemporary with [corrected] Australopithecus garhi). Results frequently vary depending on whether the data are univariate or multivariate. Unique limb proportions and fragmented remains complicate the choice of estimator. We are usually left in the end with the classical calibrator as the best choice. It is the maximum likelihood estimator that performs best overall, especially in scenarios where extrapolation occurs away from the mean of the reference sample. The new diagnostic appears to be a quick and efficient way to determine at the outset whether extrapolation exists in size and/or shape of the long bones between the reference sample and the target specimen.

Axial and appendicular skeleton of Homo antecessor

The human trunk and limb bones recovered from the Gran Dolina site, in the Sierra de Atapuerca (Burgos, Spain) are studied. All these fossils were excavated at the level called TD6 between 1994 and 1995 and have been dated in excess of 780,000 years ago. These remains have been recently attributed to a new Homo species named Homo antecessor. Axial (vertebrae and ribs) and part of the appendicular (clavicles, radii, femur and patellae) skeleton are studied here. Hand and foot bones have been studied elsewhere (Lorenzo et al., 1999). Four is the minimum number of individuals represented by the postcranial remains recovered up to now. All elements are briefly described anatomically, measured and compared with other fossil hominids and modern humans in order to establish, as far as possible, what postcranial morphology characterized this new species of our genus. The H. antecessor postcrania, generally, display a set of morphological traits that are more similar to modern humans than to the Middle and Upper Pleistocene European hominids. Our results do not contradict the previous phylogenetic analysis, i.e., that H. antecessor represents the last common ancestor for H. sapiens (modern humans) and H. neanderthalensis (Neandertals).

Estimation of African ape body length from femur length

The estimation from long bone lengths of stature in humans or body size in apes has a deep history in physical anthropology. To date, we can enumerate at least five different statistical methods for making such estimations. These methods are: (1) the regression of body length on long bone length (inverse calibration), (2) regression of long bone length on body length followed by solving for body length (classical calibration), (3) major axis regression of body length on long bone length, (4) reduced major axis regression of body length on long bone length, and (5) use of a long bone/body length ratio. We examine some of the statistical properties of these estimators using a large sample of humans (n = 2053) to derive the estimators, and applying them to smaller samples of Pan troglodytes (n = 42), Pan paniscus (n = 8), and Gorilla gorilla (n = 35). Based on the root mean-squared error (RMSE), the reduced major axis is the preferred estimator for body length in the combined Pan sample. However, inverse calibration is the best estimator for body length in gorillas based on the RMSE. Many estimators grossly underestimate body length in the apes. Differences in allometries between humans and great apes are obvious, but it is important to show the assumptions necessary in estimating body size from fossil remains, especially when isolated long bones are recovered and the global allometry is consequently unknown.

Locomotor activity differences between sympatric patas monkeys (Erythrocebus patas) and vervet monkeys (Cercopithecus aethiops): implications for the evolution of long hindlimb length in Homo

Homo erectus is notable for its taller stature and longer lower limbs relative to earlier hominids, but the selective pressures favoring such long limbs are unclear. Among anthropoid primates, patas monkeys (Erythrocebus patas) and extant hominids share several extreme characteristics involved with foraging and movement, including the relatively longest lower limb proportions, longest daily travel distances and largest home ranges for their body or group size, occupancy of some of the driest habitats, and very efficient thermoregulatory systems. We suggest that patas monkeys are an appropriate behavioral model with which to speculate on the selective pressures that might have operated on H. erectus to increase lower limb length. Here, in a comparison of the locomotor activities of patas monkeys and sympatric, closely related vervet monkeys (Cercopithecus aethiops), we provide evidence for the hypothesis that patas use their long stride more to increase foraging efficiency while walking than to run, either from predators or otherwise.