Out of Africa: modern human origins special feature: the meaning of neandertal skeletal morphology

The effect of bi-iliac breadth on core body temperature

Thermoregulation is argued to be an important factor influencing body breadth in hominins based on the relationship of surface area to body mass first proposed by Bergmann. Selection for a narrow thorax, and thus a narrow pelvis, increases body surface area relative to body mass, which could be beneficial in hot climates if it leads to a decrease in core body temperature. However, the relationship between pelvic breadth and thermoregulation in humans has not been established. Although previous work has shown that bi-iliac breadth is significantly positively associated with latitude in humans, we lack an understanding of whether this association is due to climate-related selection, neutral evolutionary processes, or other selective pressures. A missing piece of the puzzle is whether body breadth at the iliac blades is an important factor in thermoregulation. Here, we examine this in a mixed-sex sample of 28 adult runners who ran for one hour at 3.14 m s-1 in a variety of climatic conditions while their core body temperatures were measured using internal temperature sensors. The association of maximum core temperature with anthropometric and demographic variables such as age, sex, mass, body fat percentage, and bi-iliac breadth was analyzed using a linear mixed-effect model. Due to the small sample size, the model was also bootstrapped. We found that an increase in absolute bi-iliac breadth was significantly associated with an increase in maximum core temperature. Overall, this preliminary analysis suggests a link between variation in bi-iliac breadth and maximum core body temperature during running, but further investigation is needed.

Uncovering the adult morphology of the forearm bones from the Sima de los Huesos Site in Atapuerca (Spain), with comments on biomechanical features

The forearm skeleton is composed of two bones: the radius and the ulna. This is closely related to manipulative movements. The ulna is part of the elbow joint, whereas the radius and ulna together with the scaphoid and lunate bones, form the wrist joints. Thus, morphofunctional analysis of the adult Sima de los Huesos (SH) forearm bones, provides clues about manipulative activities in one Pleistocene population. From 1976 to the present, over 7000 human fossils have been recovered from the SH site. The radial sample comprised 98 labeled fragments, of which 49 belonged to adult individuals, representing at least 7 individuals. The ulnar sample included 31 labeled adult fossils representing at least nine individuals. In this study, we describe the SH radii and ulnae and analyze their functional implications for manipulative and forearm movements. We confirmed that the SH radii are long and curved, with variations in robusticity and radial tuberosity orientation. The SH ulnae are characterized by an anteriorly oriented trochlear notch, a massive olecranon process, an obliquely oriented radial notch, a blunt and short supinator crest, a gracile and curved diaphysis, and a round and anteriorly oriented pronator crests. In general, they exhibit Neanderthal morphology. The SH collection provides a unique opportunity to conduct morphological analyses of these bones in the Middle Pleistocene population.

Main morphological characteristics and sexual dimorphism of hominin adult femora from the Sima de los Huesos Middle Pleistocene site (Sierra de Atapuerca, Spain)

The excellent fossil record from Sima de los Huesos (SH) includes three well-known complete adult femora and several partial specimens that have not yet been published in detail. This fossil record provides an opportunity to analyze the morphology of European pre-Neandertal adult femur and its variation with different evolution patterns. Currently, there are a minimum of five adult individuals (males or females). In this study, we compiled previously published basic anatomical and biometric characteristics of SH adult femora, emphasizing the most relevant features compared to other recent and fossil hominins. The SH femora exhibited a primitive morphological pattern common to all non-Homo sapiens femora, as well as most of the Neandertal traits. Therefore, the complete Upper Pleistocene Neandertal pattern was well-established in Middle Pleistocene ancestors long before the proper Neandertals appeared. Additionally, we highlight that the SH and Neandertal femora share some morphological traits and proportions with modern humans that hold sexual significance in our species, regardless of size. Keeping this in mind, we discussed the sex determination of the complete SH specimens and re-evaluated sex allocation in two of them.

Exploring the morphology of adult tibia and fibula from Sima de los Huesos site in sierra de Atapuerca, Burgos, Spain

The analysis of the locomotor anatomy of Late Pleistocene Homo has largely focused on changes in proximal femur and pelvic morphologies, with much attention centered on the emergence of modern humans. Although much of the focus has been on changes in the proximal femur, some research has also been conducted on tibiae and, to a lesser extent, fibulae. With this in mind, we present one of the largest samples of the same population of human tibiae and fibulae from the Middle Pleistocene to determine their main characteristic traits and establish similarities and differences, primarily with those of Neanderthals and modern humans, but also with other Middle Pleistocene specimens in the fossil record. Through this study, we established that the Middle Pleistocene population from the Sima de los Huesos (Atapuerca, Burgos, Spain) had lower leg long bones similar to those of Neanderthals, although there were some important differences, such as bone length, which this fossil individuals resembled those of modern humans and not to Neanderthals. This fact is related to the crural index and leg length, even though we do not have any true association between femora and tibiae yet, it has implications for establishing locomotor efficiency and climate adaptation.

Evolutionary and functional analyses of LRP5 in archaic and extant modern humans

BACKGROUND

The human lineage has undergone a postcranial skeleton gracilization (i.e. lower bone mass and strength relative to body size) compared to other primates and archaic populations such as the Neanderthals. This gracilization has been traditionally explained by differences in the mechanical load that our ancestors exercised. However, there is growing evidence that gracilization could also be genetically influenced.

RESULTS

We have analyzed the LRP5 gene, which is known to be associated with high bone mineral density conditions, from an evolutionary and functional point of view. Taking advantage of the published genomes of archaic Homo populations, our results suggest that this gene has a complex evolutionary history both between archaic and living humans and within living human populations. In particular, we identified the presence of different selective pressures in archaics and extant modern humans, as well as evidence of positive selection in the African and South East Asian populations from the 1000 Genomes Project. Furthermore, we observed a very limited evidence of archaic introgression in this gene (only at three haplotypes of East Asian ancestry out of the 1000 Genomes), compatible with a general erasing of the fingerprint of archaic introgression due to functional differences in archaics compared to extant modern humans. In agreement with this hypothesis, we observed private mutations in the archaic genomes that we experimentally validated as putatively increasing bone mineral density. In particular, four of five archaic missense mutations affecting the first β-propeller of LRP5 displayed enhanced Wnt pathway activation, of which two also displayed reduced negative regulation.

CONCLUSIONS

In summary, these data suggest a genetic component contributing to the understanding of skeletal differences between extant modern humans and archaic Homo populations.

A regulatory variant impacting TBX1 expression contributes to basicranial morphology in Homo sapiens

Changes in gene regulatory elements play critical roles in human phenotypic divergence. However, identifying the base-pair changes responsible for the distinctive morphology of Homo sapiens remains challenging. Here, we report a noncoding single-nucleotide polymorphism (SNP), rs41298798, as a potential causal variant contributing to the morphology of the skull base and vertebral structures found in Homo sapiens. Screening for differentially regulated genes between Homo sapiens and extinct relatives revealed 13 candidate genes associated with basicranial development, with TBX1, implicated in DiGeorge syndrome, playing a pivotal role. Epigenetic markers and in silico analyses prioritized rs41298798 within a TBX1 intron for functional validation. CRISPR editing revealed that the 41-base-pair region surrounding rs41298798 modulates gene expression at 22q11.21. The derived allele of rs41298798 acts as an allele-specific enhancer mediated by E2F1, resulting in increased TBX1 expression levels compared to the ancestral allele. Tbx1-knockout mice exhibited skull base and vertebral abnormalities similar to those seen in DiGeorge syndrome. Phenotypic differences associated with TBX1 deficiency are observed between Homo sapiens and Neanderthals (Homo neanderthalensis). In conclusion, the regulatory divergence of TBX1 contributes to the formation of skull base and vertebral structures found in Homo sapiens.

Sex estimation of the adult Neandertal Regourdou 1 (Montignac, France): Implications for sexing human fossil remains

Sex is a biological trait fundamental to the study of hominin fossils. Among the many questions that can be addressed are those related to taxonomy, biological variability, sexual dimorphism, paleoobstetrics, funerary selection, and paleodemography. While new methodologies such as paleogenomics or paleoproteomics can be used to determine sex, they have not been systematically applied to Pleistocene human remains due to their destructive nature. Therefore, we estimated sex from the coxal bone of the newly discovered pelvic remains of the Regourdou 1 Neandertal (Southwest France, MIS 5) based on morphological and metric data employing two methods that have been recently revised and shown to be reliable in multiple studies. Both methods calculate posterior probabilities of the estimate. The right coxal bone of Regourdou 1 was partially reconstructed providing additional traits for sex estimation. These methods were cross validated on 14 sufficiently preserved coxal bones of specimens from the Neandertal lineage. Our results show that the Regourdou 1 individual, whose postcranial skeleton is not robust, is a male, and that previous sex attributions of comparative Neandertal specimens are largely in agreement with those obtained here. Our results encourage additional morphological research of fossil hominins in order to develop a set of methods that are applicable, reliable, and reproducible.

Finite element analysis of Neanderthal and early Homo sapiens maxillary central incisor

Neanderthal anterior teeth are very large and have a distinctive morphology characterized by robust 'shovel-shaped' crowns. These features are frequently seen as adaptive responses in dissipating heavy mechanical loads resulting from masticatory and non-masticatory activities. Although the long-standing debate surrounding this hypothesis has played a central role in paleoanthropology, is still unclear if Neanderthal anterior teeth can resist high mechanical loads or not. A novel way to answer this question is to use a multidisciplinary approach that considers together tooth architecture, dental wear and jaw movements. The aim of this study is to functionally reposition the teeth of Le Moustier 1 (a Neanderthal adolescent) and Qafzeh 9 (an early Homo sapiens adolescent) derived from wear facet mapping, occlusal fingerprint analysis and physical dental restoration methods. The restored dental arches are then used to perform finite element analysis on the left central maxillary incisor during edge-to-edge occlusion. The results show stress distribution differences between Le Moustier 1 and Qafzeh 9, with the former displaying higher tensile stress in enamel around the lingual fossa but lower concentration of stress in the lingual aspect of the root surface. These results seem to suggest that the presence of labial convexity, lingual tubercle and of a large root surface in Le Moustier 1 incisor helps in dissipating mechanical stress. The absence of these dental features in Qafzeh 9 is compensated by the presence of a thicker enamel, which helps in reducing the stress in the tooth crown.

The estimation and evolution of hominin body mass

Body mass is a critical variable in many hominin evolutionary studies, with implications for reconstructing relative brain size, diet, locomotion, subsistence strategy, and social organization. We review methods that have been proposed for estimating body mass from true and trace fossils, consider their applicability in different contexts, and the appropriateness of different modern reference samples. Recently developed techniques based on a wider range of modern populations hold promise for providing more accurate estimates in earlier hominins, although uncertainties remain, particularly in non-Homo taxa. When these methods are applied to almost 300 Late Miocene through Late Pleistocene specimens, the resulting body mass estimates fall within a 25-60 kg range for early non-Homo taxa, increase in early Homo to about 50-90 kg, then remain constant until the Terminal Pleistocene, when they decline.

Variation in ontogenetic trajectories of limb dimensions in humans is attributable to both climatic effects and neutral evolution

Previous studies showed that there is variation in ontogenetic trajectories of human limb dimensions and proportions. However, little is known about the evolutionary significance of this variation. This study used a global sample of modern human immature long bone measurements and a multivariate linear mixed-effects model to study 1) whether the variation in ontogenetic trajectories of limb dimensions is consistent with ecogeographic predictions and 2) the effects of different evolutionary forces on the variation in ontogenetic trajectories. We found that genetic relatedness arising from neutral (nonselective) evolution, allometric variation associated with the change in size, and directional effects from climate all contributed to the variation in ontogenetic trajectories of all major long bone dimensions in modern humans. After accounting for the effects of neutral evolution and holding other effects considered in the current study constant, extreme temperatures have weak, positive associations with diaphyseal length and breadth measurements, while mean temperature shows negative associations with diaphyseal dimensions. The association with extreme temperatures fits the expectations of ecogeographic rules, while the association with mean temperature may explain the observed among-group variation in intralimb indices. The association with climate is present throughout ontogeny, suggesting an explanation of adaptation by natural selection as the most likely cause. On the other hand, genetic relatedness among groups, as structured by neutral evolutionary factors, is an important consideration when interpreting skeletal morphology, even for nonadult individuals.

Review: The different adaptive trajectories in Neanderthals and Homo sapiens and their implications for contemporary human physiological variation

Neanderthals are our one of our closest evolutionary cousins, but while they evolved in Eurasia, we (anatomically modern humans, AMH) originated in Africa. This contrasting evolutionary history has led to morphological and genetic distinctions between our species. Neanderthals are characterised by a relatively stocky build, high body mass, proportionally wide bodies and shorter limbs, a bell-shaped ribcage with a wide pelvis, and a long, low cranial vault compared with AMH. Classic readings of Neanderthal morphology link many of these traits to cold climate adaptations, however these interpretations have been questioned and alternative hypotheses including behavioural factors, dietary adaptations, locomotor specialisations, evolutionary history and neutral evolutionary processes have been invoked. Compared with AMH, Neanderthals may have been adapted for strength and power rather than endurance and may have consumed a diet high in animal products. However, reviewing these hypotheses highlights a number of limitations in our understanding of contemporary human physiology and metabolism, including the relationship between climate and morphology in AMH and Neanderthals, physiological limits on protein consumption, and the relationship between gut morphology and diet. As various relevant factors are clearly linked (e.g. diet, behaviour, metabolism, morphology, activity), ultimately a more integrated approach may be needed to fully understand Neanderthal biology. Variation among contemporary AMHs may offer, with caveats, a useful model for understanding the evolution of both Neanderthal and modern human characteristics, which in turn may further deepen our understanding of variability within and between contemporary humans. Neanderthals; Anatomically modern humans; morphology; climate adaptation; power adaptations; metabolism; diet; physiology; endurance running.

The contribution of Neanderthal introgression to modern human traits

Neanderthals, our closest extinct relatives, lived in western Eurasia from 400,000 years ago until they went extinct around 40,000 years ago. DNA retrieved from ancient specimens revealed that Neanderthals mated with modern human contemporaries. As a consequence, introgressed Neanderthal DNA survives scattered across the human genome such that 1-4% of the genome of present-day people outside Africa are inherited from Neanderthal ancestors. Patterns of Neanderthal introgressed genomic sequences suggest that Neanderthal alleles had distinct fates in the modern human genetic background. Some Neanderthal alleles facilitated human adaptation to new environments such as novel climate conditions, UV exposure levels and pathogens, while others had deleterious consequences. Here, we review the body of work on Neanderthal introgression over the past decade. We describe how evolutionary forces shaped the genomic landscape of Neanderthal introgression and highlight the impact of introgressed alleles on human biology and phenotypic variation.

Variation in human 3D trunk shape and its functional implications in hominin evolution

This study investigates the contribution of external trunk morphology and posture to running performance in an evolutionary framework. It has been proposed that the evolution from primitive to derived features of torso shape involved changes from a mediolaterally wider into a narrower, and antero-posteriorly deeper into a shallower, more lightly built external trunk configuration, possibly in relation to habitat-related changes in locomotor and running behaviour. In this context we produced experimental data to address the hypothesis that medio-laterally narrow and antero-posteriorly shallow torso morphologies favour endurance running capacities. We used 3D geometric morphometrics to relate external 3D trunk shape of trained, young male volunteers (N = 27) to variation in running velocities during different workloads determined at 45–50%, 70% and 85% of heart rate reserve (HRR) and maximum velocity. Below 85% HRR no relationship existed between torso shape and running velocity. However, at 85% HRR and, more clearly, at maximum velocity, we found highly statistically significant relations between external torso shape and running performance. Among all trained subjects those with a relatively narrow, flat torso, a small thoracic kyphosis and a more pronounced lumbar lordosis achieved significantly higher running velocities. These results support the hypothesis that external trunk morphology relates to running performance. Low thoracic kyphosis with a flatter ribcage may affect positively respiratory biomechanics, while increased lordosis affects trunk posture and may be beneficial for lower limb biomechanics related to leg return. Assuming that running workload at 45–50% HRR occurs within aerobic metabolism, our results may imply that external torso shape is unrelated to the evolution of endurance running performance.

Epigenomic Modifications in Modern and Ancient Genomes

Epigenetic changes have been identified as a major driver of fundamental metabolic pathways. More specifically, the importance of epigenetic regulatory mechanisms for biological processes like speciation and embryogenesis has been well documented and revealed the direct link between epigenetic modifications and various diseases. In this review, we focus on epigenetic changes in animals with special attention on human DNA methylation utilizing ancient and modern genomes. Acknowledging the latest developments in ancient DNA research, we further discuss paleoepigenomic approaches as the only means to infer epigenetic changes in the past. Investigating genome-wide methylation patterns of ancient humans may ultimately yield in a more comprehensive understanding of how our ancestors have adapted to the changing environment, and modified their lifestyles accordingly. We discuss the difficulties of working with ancient DNA in particular utilizing paleoepigenomic approaches, and assess new paleoepigenomic data, which might be helpful in future studies.

Unique foot posture in Neanderthals reflects their body mass and high mechanical stress

Neanderthal foot bone proportions and morphology are mostly indistinguishable from those of Homo sapiens, with the exception of several distinct Neanderthal features in the talus. The biomechanical implications of these distinct talar features remain contentious, fueling debate around the adaptive meaning of this distinctiveness. With the aim of clarifying this controversy, we test phylogenetic and behavioral factors as possible contributors, comparing tali of 10 Neanderthals and 81 H. sapiens (Upper Paleolithic and Holocene hunter-gatherers, agriculturalists, and postindustrial group) along with the Clark Howell talus (Omo, Ethiopia). Variation in external talar structures was assessed through geometric morphometric methods, while bone volume fraction and degree of anisotropy were quantified in a subsample (n = 45). Finally, covariation between point clouds of site-specific trabecular variables and surface landmark coordinates was assessed. Our results show that although Neanderthal talar external and internal morphologies were distinct from those of H. sapiens groups, shape did not significantly covary with either bone volume fraction or degree of anisotropy, suggesting limited covariation between external and internal talar structures. Neanderthal external talar morphology reflects ancestral retentions, along with various adaptations to high levels of mobility correlated to their presumably unshod hunter-gatherer lifestyle. This pairs with their high site-specific trabecular bone volume fraction and anisotropy, suggesting intense and consistently oriented locomotor loading, respectively. Relative to H.sapiens, Neanderthals exhibit differences in the talocrural joint that are potentially attributable to cultural and locomotor behavior dissimilarity, a talonavicular joint that mixes ancestral and functional traits, and a derived subtalar joint that suggests a predisposition for a pronated foot during stance phase. Overall, Neanderthal talar variation is attributable to mobility strategy and phylogenesis, while H. sapiens talar variation results from the same factors plus footwear. Our results suggest that greater Neanderthal body mass and/or higher mechanical stress uniquely led to their habitually pronated foot posture.

Effects of hybridization on pelvic morphology: A macaque model

Ancient DNA analyses have shown that interbreeding between hominin taxa occurred multiple times. Although admixture is often reflected in skeletal phenotype, the relationship between the two remains poorly understood, hampering interpretation of the hominin fossil record. Direct study of this relationship is often impossible due to the paucity of hominin fossils and difficulties retrieving ancient genetic material. Here, we use a sample of known ancestry hybrids between two closely related nonhuman primate taxa (Indian and Chinese Macaca mulatta) to investigate the effect of admixture on skeletal morphology. We focus on pelvic shape, which has potential fitness implications in hybrids, as mismatches between maternal pelvic and fetal cranial morphology are often fatal to mother and offspring. As the pelvis is also one of the skeletal regions that differs most between Homo sapiens and Neanderthals, investigating the pelvic consequences of interbreeding could be informative regarding the viability of their hybrids. We find that the effect of admixture in M. mulatta is small and proportional to the relatively small morphological difference between the parent taxa. Sexual dimorphism appears to be the main determinant of pelvic shape in M. mulatta. The lack of difference in pelvic shape between Chinese and Indian M. mulatta is in contrast to that between Neanderthals and H. sapiens, despite a similar split time (in generations) between the hybridizing pairs. Greater phenotypic divergence between hominins may relate to adaptations to disparate environments but may also highlight how the unique degree of cultural buffering in hominins allowed for greater neutral divergence. In contrast to some previous work identifying extreme morphologies in first- and second-generation hybrids, here the relationship between pelvic shape and admixture is linear. This linearity may be because most sampled animals have a multigenerational admixture history or because of relatively high constraints on the pelvis compared with other skeletal regions.

Early development of the Neanderthal ribcage reveals a different body shape at birth compared to modern humans

Ontogenetic studies provide clues for understanding important paleobiological aspects of extinct species. When compared to that of modern humans, the adult Neanderthal thorax was shorter, deeper, and wider. This is related to the wide Neanderthal body and is consistent with their hypothetical large requirements for energy and oxygen. Whether these differences were already established at birth or appeared later during development is unknown. To delve into this question, we use virtual reconstruction tools and geometric morphometrics to recover the 3D morphology of the ribcages of four Neanderthal individuals from birth to around 3 years old: Mezmaiskaya 1, Le Moustier 2, Dederiyeh 1, and Roc de Marsal. Our results indicate that the comparatively deep and short ribcage of the Neanderthals was already present at birth, as were other skeletal species-specific traits. This morphology possibly represents the plesiomorphic condition shared with Homo erectus, and it is likely linked to large energetic requirements.

A high-coverage Neandertal genome from Chagyrskaya Cave

We sequenced the genome of a Neandertal from Chagyrskaya Cave in the Altai Mountains, Russia, to 27-fold genomic coverage. We show that this Neandertal was a female and that she was more related to Neandertals in western Eurasia [Prüfer et al., Science 358, 655-658 (2017); Hajdinjak et al., Nature 555, 652-656 (2018)] than to Neandertals who lived earlier in Denisova Cave [Prüfer et al., Nature 505, 43-49 (2014)], which is located about 100 km away. About 12.9% of the Chagyrskaya genome is spanned by homozygous regions that are between 2.5 and 10 centiMorgans (cM) long. This is consistent with the fact that Siberian Neandertals lived in relatively isolated populations of less than 60 individuals. In contrast, a Neandertal from Europe, a Denisovan from the Altai Mountains, and ancient modern humans seem to have lived in populations of larger sizes. The availability of three Neandertal genomes of high quality allows a view of genetic features that were unique to Neandertals and that are likely to have been at high frequency among them. We find that genes highly expressed in the striatum in the basal ganglia of the brain carry more amino-acid-changing substitutions than genes expressed elsewhere in the brain, suggesting that the striatum may have evolved unique functions in Neandertals.

Reconstructing Denisovan Anatomy Using DNA Methylation Maps

Denisovans are an extinct group of humans whose morphology remains unknown. Here, we present a method for reconstructing skeletal morphology using DNA methylation patterns. Our method is based on linking unidirectional methylation changes to loss-of-function phenotypes. We tested performance by reconstructing Neanderthal and chimpanzee skeletal morphologies and obtained >85% precision in identifying divergent traits. We then applied this method to the Denisovan and offer a putative morphological profile. We suggest that Denisovans likely shared with Neanderthals traits such as an elongated face and a wide pelvis. We also identify Denisovan-derived changes, such as an increased dental arch and lateral cranial expansion. Our predictions match the only morphologically informative Denisovan bone to date, as well as the Xuchang skull, which was suggested by some to be a Denisovan. We conclude that DNA methylation can be used to reconstruct anatomical features, including some that do not survive in the fossil record.

The study of the lower limb entheses in the Neanderthal sample from El Sidrón (Asturias, Spain): How much musculoskeletal variability did Neanderthals accumulate?

Entheses have rarely been systematically studied in the field of human evolution. However, the investigation of their morphological variability (e.g., robusticity) could provide new insight into their evolutionary significance in the European Neanderthal populations. The aim of this work is to study the entheses and joint features of the lower limbs of El Sidrón Neanderthals (Spain; 49 ka), using standardized scoring methods developed on modern samples. Paleobiology, growth, and development of both juveniles and adults from El Sidrón are studied and compared with those of Krapina Neanderthals (Croatia, 130 ka) and extant humans. The morphological patterns of the gluteus maximus and vastus intermedius entheses in El Sidrón, Krapina, and modern humans differ from one another. Both Neanderthal groups show a definite enthesis design for the gluteus maximus, with little intrapopulation variability with respect to modern humans, who are characterized by a wider range of morphological variability. The gluteus maximus enthesis in the El Sidrón sample shows the osseous features of fibrous entheses, as in modern humans, whereas the Krapina sample shows the aspects of fibrocartilaginous ones. The morphology and anatomical pattern of this enthesis has already been established during growth in all three human groups. One of two and three of five adult femurs from El Sidrón and from Krapina, respectively, show the imprint of the vastus intermedius, which is absent among juveniles from those Neanderthal samples and in modern samples. The scant intrapopulation and the high interpopulation variability in the two Neanderthal samples is likely due to a long-term history of small, isolated populations with high levels of inbreeding, who also lived in different ecological conditions. The comparison of different anatomical entheseal patterns (fibrous vs. fibrocartilaginous) in the Neanderthals and modern humans provides additional elements in the discussion of their functional and genetic origin.

A descriptive and comparative study of two Early Pleistocene immature scapulae from the TD6.2 level of the Gran Dolina cave site (Sierra de Atapuerca, Spain)

Here we present the descriptive and comparative study of two immature scapulae recovered from the TD6.2 level of the Gran Dolina cave site (Sierra de Atapuerca, Spain) and assigned to Homo antecessor. This is the first time that data on the morphology and dimensions of the scapulae of a European late Early Pleistocene hominin population are provided. Considering the state of development and the linear dimensions, the scapula ATD6-116 could belong to a child of about 2-4 years. The morphology of ATD6-116 clearly departs from that of the Australopithecus afarensis juvenile specimen DIK-1-1, pointing to functional differences in locomotor behavior between Australopithecus and the late Early Pleistocene hominins. The immature scapula ATD6-118 belonged to an immature individual with a development of the scapula equivalent to that of adolescents of recent human populations. The scapulae ATD6-118 and KNM-WT 15000 present a similar state of development. Although the scapula KNM-WT 15000 is clearly larger than ATD6-118, these two specimens share some characteristics such as their relative narrowness and the value of the axilloglenoid and spinoglenoid angles. The glenoid fossa of ATD6-116 show a lateral orientation, whereas in ATD6-118 the glenoid fossa is slightly cranially oriented, but still within the range of variation of modern humans. The glenoid index of both ATD6-116 and ATD6-118 is low in accordance to the values usually observed in other early hominins, thus showing the primitive condition for this feature. Both scapulae show a ventrally placed axillary sulcus. The presence of this primitive feature in ATD-116 confirms that the shape of the axillary border has a genetic basis and it is not related to physical activity.

Anterior tooth-use behaviors among early modern humans and Neandertals

Early modern humans (EMH) are often touted as behaviorally advanced to Neandertals, with more sophisticated technologies, expanded resource exploitation, and more complex clothing production. However, recent analyses have indicated that Neandertals were more nuanced in their behavioral adaptations, with the production of the Châtelperronian technocomplex, the processing and cooking of plant foods, and differences in behavioral adaptations according to habitat. This study adds to this debate by addressing the behavioral strategies of EMH (n = 30) within the context of non-dietary anterior tooth-use behaviors to glean possible differences between them and their Neandertal (n = 45) counterparts. High-resolution casts of permanent anterior teeth were used to collect microwear textures of fossil and comparative bioarchaeological samples using a Sensofar white-light confocal profiler with a 100x objective lens. Labial surfaces were scanned, totaling a work envelope of 204 x 276 μm for each individual. The microwear textures were examined for post-mortem damage and uploaded to SSFA software packages for surface characterization. Statistical analyses were performed to examine differences in central tendencies and distributions of anisotropy and textural fill volume variables among the EMH sample itself by habitat, location, and time interval, and between the EMH and Neandertal samples by habitat and location. Descriptive statistics for the EMH sample were compared to seven bioarchaeological samples (n = 156) that utilized different tooth-use behaviors to better elucidate specific activities that may have been performed by EMH. Results show no significant differences between the means within the EMH sample by habitat, location, or time interval. Furthermore, there are no significant differences found here between EMH and Neandertals. Comparisons to the bioarchaeological samples suggest both fossil groups participated in clamping and grasping activities. These results indicate that EMH and Neandertals were similar in their non-dietary anterior tooth-use behaviors and provide additional evidence for overlapping behavioral strategies employed by these two hominins.

Beyond Bergmann's rule: Global variability in human body composition is associated with annual average precipitation and annual temperature volatility

OBJECTIVES

Human populations exhibit substantial geographical variability in body size and shape. However, the ecological stresses underlying this morphological variability remain poorly understood. The prevailing evolutionary explanation, "Bergmann's rule" assumes that morphological variability represents an adaptive response to average thermal conditions. We hypothesized that other climate factors-annual average precipitation, a marker of ecological productivity and inter-annual temperature volatility, a marker of infectious disease spikes-may also contribute to variability in body composition.

MATERIALS AND METHODS

We explored this hypothesis by examining associations between these climate factors and geographic variability in body composition across 133 male and 105 female populations from nonindustrialized settings. We used monthly climate data over 113 years (1901-2013) to develop new climate indices for all worldwide land areas. We stratified our analyses by hot/cold setting (>/<20°C).

RESULTS

In hot environments, lean mass increased as predicted in association with ecological productivity, and decreased in association with ecological volatility. Conversely, levels of body fat increased in association with temperature volatility and precipitation. However, in cold settings, equivalent associations were only partially consistent with our hypotheses, and there was suggestive evidence of sex differences in these associations.

DISCUSSION

Beyond associations with mean annual temperature predicted by Bergmann's rule, variability in human body composition is also associated with mean annual temperature and inter-annual temperature volatility, with these associations further differing between hot and cold settings. Collectively, our results suggest that associations of human body composition with climate are complex for both physique (fat-free mass) and energy stores (adiposity).

Human paleoneurology: Shaping cortical evolution in fossil hominids

Evolutionary neuroanatomy must integrate two different sources of information, namely from fossil and from living species. Fossils supply information concerning the process of evolution, whereas living species supply information on the product of evolution. Unfortunately, the fossil record is partial and fragmented, and often cannot support validations for specific evolutionary hypotheses. Living species can provide more comprehensive indications, but they do not represent ancestral groups or primitive forms. Macaques or chimpanzees are frequently used as proxy for human ancestral conditions, despite the fact they are divergent and specialized lineages, with their own biological features. Similarly, in paleoanthropology independent lineages (such as Neanderthals) should not be confused with ancestral modern human stages. In this comparative framework, paleoneurology deals with the analysis of the endocranial cavity in extinct species, in order to make inferences on brain evolution. A main target of this field is to distinguish the endocranial variations due to brain changes, from those due to cranial constraints. Digital anatomy and computed morphometrics have provided major advances in this field. However, brains and endocasts can be hard to analyze with geometrical models, because of uncertainties due to the localization of cortical landmarks and boundaries. The study of the evolution of the parietal cortex supplies an interesting case-study in which paleontological and neontological data can integrate and test evolutionary hypotheses based on multiple sources of evidence. The relationships with visuospatial functions and brain-body-tool integration stress further that the analysis of the cognitive system should go beyond the neural boundaries of the brain.

Living on the edge: Was demographic weakness the cause of Neanderthal demise?

The causes of disappearance of the Neanderthals, the only human population living in Europe before the arrival of Homo sapiens, have been debated for decades by the scientific community. Different hypotheses have been advanced to explain this demise, such as cognitive, adaptive and cultural inferiority of Neanderthals. Here, we investigate the disappearance of Neanderthals by examining the extent of demographic changes needed over a period of 10,000 years (yrs) to lead to their extinction. In regard to such fossil populations, we inferred demographic parameters from present day and past hunter-gatherer populations, and from bio-anthropological rules. We used demographic modeling and simulations to identify the set of plausible demographic parameters of the Neanderthal population compatible with the observed dynamics, and to explore the circumstances under which they might have led to the disappearance of Neanderthals. A slight (<4%) but continuous decrease in the fertility rate of younger Neanderthal women could have had a significant impact on these dynamics, and could have precipitated their demise. Our results open the way to non-catastrophic events as plausible explanations for Neanderthal extinction.

Big Choanae, Larger Face: Scaling Patterns Between Cranial Airways in Modern Humans and African Apes and Their Significance in Middle and Late Pleistocene Hominin Facial Evolution

This study aimed to understand the ontogenetic and allometric relationships in scaling between the anterior and posterior openings of the cranial airways and facial size, in order to shed light on the mechanisms that might underlie the evolution of a large face and large airways in Middle Pleistocene hominins and Neandertals. Sizes were calculated from 3D landmarks measured on the facial skeleton and airway structures of 403 skulls from two ontogenetic series of H. sapiens and P. troglodytes, an adult sample of gorillas and 11 Middle Pleistocene hominins and Neandertals. RMA regression models were used to compare the patterns in scaling between the anterior and posterior airways in relation to overall facial size. Our results show that the size of the anterior airways correlates more positively with facial size than the size of the posterior airways. This ontogenetic mechanism could explain the large faces and noses in the Neandertal lineage despite the adverse effects of such a phenotype for respiratory air-conditioning in cold climates. A large facial size could be a developmentally constrained consequence of generating airways large enough to provide the necessary oxygen for high energy demand in this large-brained and heavy-bodied hominin lineage.

Morphological trends in arcade shape and size in Middle Pleistocene Homo

OBJECTIVES

Middle Pleistocene fossil hominins, often summarized as Homo heidelbergensis sensu lato, are difficult to interpret due to a fragmentary fossil record and ambiguous combinations of primitive and derived characters. Here, we focus on one aspect of facial shape and analyze shape variation of the dental arcades of these fossils together with other Homo individuals.

MATERIALS AND METHODS

Three-dimensional landmark data were collected on computed tomographic scans and surface scans of Middle Pleistocene fossil hominins (n = 8), Homo erectus s.l. (n = 4), Homo antecessor (n = 1), Homo neanderthalensis (n = 13), recent (n = 52) and fossil (n = 19) Homo sapiens. To increase sample size, we used multiple multivariate regression to reconstruct complementary arches for isolated mandibles, and explored size and shape differences among maxillary arcades.

RESULTS

The shape of the dental arcade in H. erectus s.l. and H. antecessor differs markedly from both Neanderthals and H. sapiens. The latter two show subtle but consistent differences in arcade length and width. Shape variation among Middle Pleistocene fossil hominins does not exceed the amount of variation of other species, but includes individuals with more primitive and more derived morphology, all more similar to Neanderthals and H. sapiens than to H. erectus s.l.

DISCUSSION

Although our results cannot reject the hypothesis that the Middle Pleistocene fossil hominins belong to a single species, their shape variation comprises a more primitive morph that represents a likely candidate for the shape of the last common ancestor of Neanderthals and H. sapiens, and a more derived morph resembling Neanderthals. The arcade shape difference between Neanderthals and H. sapiens might be related to different ways to withstand mechanical stress.

Ribcage measurements indicate greater lung capacity in Neanderthals and Lower Pleistocene hominins compared to modern humans

Our most recent fossil relatives, the Neanderthals, had a large brain and a very heavy body compared to modern humans. This type of body requires high levels of energetic intake. While food (meat and fat consumption) is a source of energy, oxygen via respiration is also necessary for metabolism. We would therefore expect Neanderthals to have large respiratory capacities. Here we estimate the pulmonary capacities of Neanderthals, based on costal measurements and physiological data from a modern human comparative sample. The Kebara 2 male had a lung volume of about 9.04 l; Tabun C1, a female individual, a lung volume of 5.85 l; and a Neanderthal from the El Sidrón site, a lung volume of 9.03 l. These volumes are approximately 20% greater than the corresponding volumes of modern humans of the same body size and sex. These results show that the Neanderthal body was highly sensitive to energy supply.

Daniel García-Martínez et al. report Neanderthal lung volume estimates based on measurements from rib bone fossils and lung capacity data from modern humans. They estimate that Neanderthal individuals had approximately 20% higher lung capacity than modern humans, possibly due to higher energy requirements.

Computer simulations show that Neanderthal facial morphology represents adaptation to cold and high energy demands, but not heavy biting

Three adaptive hypotheses have been forwarded to explain the distinctive Neanderthal face: (i) an improved ability to accommodate high anterior bite forces, (ii) more effective conditioning of cold and/or dry air and, (iii) adaptation to facilitate greater ventilatory demands. We test these hypotheses using three-dimensional models of Neanderthals, modern humans, and a close outgroup (Homo heidelbergensis), applying finite-element analysis (FEA) and computational fluid dynamics (CFD). This is the most comprehensive application of either approach applied to date and the first to include both. FEA reveals few differences between H. heidelbergensis, modern humans, and Neanderthals in their capacities to sustain high anterior tooth loadings. CFD shows that the nasal cavities of Neanderthals and especially modern humans condition air more efficiently than does that of H. heidelbergensis, suggesting that both evolved to better withstand cold and/or dry climates than less derived Homo We further find that Neanderthals could move considerably more air through the nasal pathway than could H. heidelbergensis or modern humans, consistent with the propositions that, relative to our outgroup Homo, Neanderthal facial morphology evolved to reflect improved capacities to better condition cold, dry air, and, to move greater air volumes in response to higher energetic requirements.

What Does Nasal Cavity Size Tell us about Functional Nasal Airways?

Studies on dry human skulls have shown that nasal cavity (NC) morphology varies with eco-geographic factors. These findings have been used by some authors to interpret the facial morphology of Neanderthals. However, respiratory and air-conditioning functions are primarily carried out by the nasal airways (NA), which are delimited by mucosa. The aims of this study were to test whether: (1) NC volume (V) and surface-area-to-volume ratio (SA/ V) are proportional to NA counterparts; (2) measurements for male NC and NA are larger than in females; (3) the centroid size (CS) of a set of landmarks measured on NC provides a reliable proxy for NC V. Head CT (computed tomography) images of adult patients (N = 30) at the University Hospital of Bordeaux were selected retrospectively. NA were defined by segmenting the lumen corresponding to the functional volume. NC was defined by adding to NA the soft tissues delimited by the bones forming the NC. The coordinates of 16 landmarks measured on NC bones were recorded. A rather low correlation was found between NA and NC V while NA SA/V and NC SA/V were not correlated. No significant differences were found between male and female NA and NC measurements. A rather low correlation was found between NC Vand NC CS. If these preliminary results were to be confirmed by future studies, results using NC as a proxy for NA focusing on air-conditioning and respiratory energetics might need to be re-interpreted.

A reassessment of the Montmaurin-La Niche mandible (Haute Garonne, France) in the context of European Pleistocene human evolution

We here present a comparative study of the Montmaurin-LN Middle Pleistocene mandible (Haute-Garonne, France). This mandible, of which its right and left molar series are preserved in situ, was found in La Niche cave (Montmaurin's karst system) in 1949, and was first attributed to the 'Mindel-Riss' interglacial (= MIS 9 to 11) based on its geological context. Later studies based on geological and faunal evidence have attributed the Montmaurin-LN mandible to MIS 7. Following a detailed morphological and metric comparative study of the mandible in the 1970s, it was interpreted in the light of a still limited fossil record and the prevailing paradigm back then. Waiting for geochronological studies in the forthcoming years, here we review the main morphological and metrical features of this mandible and its molars, which have been reassessed in the framework of a remarkably enlarged Pleistocene fossil record since the mandible was first described, and our current, more in-depth understanding of human evolution in Europe. Using a selection of mandibular features with potential taxonomic signal we have found that the Montmaurin-LN mandible shares only a few derived traits with Neandertals. Our analyses reveal that this mandible is more closely related to the ancient specimens from the African and Eurasian Early and Middle Pleistocene, particularly due to the presence of primitive features of the Homo clade. In contrast, the external morphology of the molars is clearly similar to that of Neandertals. The results are assessed in the light of the present competing hypotheses used to explain the European hominin fossil record.

Twentieth anniversary of Homo antecessor (1997-2017): a review

It has been twenty years since diagnosis and publication of the species Homo antecessor.¹ Since then, new human fossils recovered from the TD6 level of the Gran Dolina site (Sierra de Atapuerca, northern Spain) have helped to refine its taxonomic and phylogenetic position. In this paper, we present a synthesis of the most characteristic features of this species, as well as our interpretation derived from the latest investigations. We focus on the phylogenetic interpretation of Homo antecessor, taking into account the most recent paleogenetic analyses and a reassessment of the European Middle Pleistocene hominin record. We try to show that, twenty years after its publication, H. antecessor provides a good opportunity to address the morphology of the last common ancestor of Neandertals and modern humans.

Detecting ancient positive selection in humans using extended lineage sorting

Natural selection that affected modern humans early in their evolution has likely shaped some of the traits that set present-day humans apart from their closest extinct and living relatives. The ability to detect ancient natural selection in the human genome could provide insights into the molecular basis for these human-specific traits. Here, we introduce a method for detecting ancient selective sweeps by scanning for extended genomic regions where our closest extinct relatives, Neandertals and Denisovans, fall outside of the present-day human variation. Regions that are unusually long indicate the presence of lineages that reached fixation in the human population faster than expected under neutral evolution. Using simulations, we show that the method is able to detect ancient events of positive selection and that it can differentiate those from background selection. Applying our method to the 1000 Genomes data set, we find evidence for ancient selective sweeps favoring regulatory changes and present a list of genomic regions that are predicted to underlie positively selected human specific traits.

The Omo-Kibish I pelvis

Omo-Kibish I (Omo I) from southern Ethiopia is the oldest anatomically modern Homo sapiens skeleton currently known (196 ± 5 ka). A partial hipbone (os coxae) of Omo I was recovered more than 30 years after the first portion of the skeleton was recovered, a find which is significant because human pelves can be informative about an individual's sex, age-at-death, body size, obstetrics and parturition, and trunk morphology. Recent human pelves are distinct from earlier Pleistocene Homo spp. pelves because they are mediolaterally narrower in bispinous breadth, have more vertically oriented ilia, lack a well-developed iliac pillar, and have distinct pubic morphology. The pelvis of Omo I provides an opportunity to test whether the earliest modern humans had the pelvic morphology characteristic of modern humans today and to shed light onto the paleobiology of the earliest humans. Here, we formally describe the preservation and morphology of the Omo I hipbone, and quantitatively and qualitatively compare the hipbone to recent humans and relevant fossil Homo. The Omo I hipbone is modern human in appearance, displaying a moderate iliac tubercle (suggesting a reduced iliac pillar) and an ilium that is not as laterally flaring as earlier Homo. Among those examined in this study, the Omo I ischium is most similar in shape to (but substantially larger than) that of recent Sudanese people. Omo I has features that suggest this skeleton belonged to a female. The stature estimates in this study were derived from multiple bones from the upper and lower part of the body, and suggest that there may be differences in the upper and lower limb proportions of the earliest modern humans compared to recent humans. The large size and robusticity of the Omo I pelvis is in agreement with other studies that have found that modern human reduction in postcranial robusticity occurred later in our evolutionary history.

Evolutionary anatomy of the Neandertal ulna and radius in the light of the new El Sidrón sample

This paper aims to improve our understanding of the phylogenetic trait polarity related to hominin forearm evolution, in particular those traits traditionally defined as "Neandertal features." To this aim, twelve adult and adolescent fragmented forelimb elements (including ulnae and radii) of Homo neanderthalensis recovered from the site of El Sidrón (Asturias, Spain) were examined comparatively using three-dimensional geometric and traditional morphometrics. Mean centroid size and shape comparisons, principal components analysis, and phylogenetic signal analysis were undertaken. Our investigations revealed that the proximal region of the ulna discriminated best between Neandertals and modern humans, with fewer taxonomically-informative features in the distal ulna and radius. Compared to modern humans, the divergent features in the Neandertal ulna are an increase in olecranon breadth (a derived trait), lower coronoid length (primitive), and anterior orientation of the trochlear notch (primitive). In the Neandertal radius, we observe a larger neck length (primitive), medial orientation of the radial tubercle (secondarily primitive), and a curved diaphysis (secondarily primitive). Anatomically, we identified three units of evolutionary change: 1) the olecranon and its fossa, 2) the coronoid-radius neck complex, and 3) the tubercle and radial diaphysis. Based on our data, forearm evolution followed a mosaic pattern in which some features were inherited from a pre-Homo ancestor, others originated in some post-ergaster and pre-antecessor populations, and other characters emerged in the specific Homo sapiens and H. neanderthalensis lineages, sometimes appearing as secondarily primitive. Future investigations might consider the diverse phylogenetic origin of apomorphies while at the same time seeking to elucidate their functional meaning.

A muscular imprint on the anterolateral surface of the proximal femurs of the Krapina Neandertal collection

OBJECTIVES

The purpose of this study is to report and interpret a feature on the anterolateral surface of the proximal femurs of the Krapina hominid collection that we briefly described in 2006 (Periodicum Biologorum, 108, 319-329).

MATERIALS AND METHODS

We recorded the presence or absence of the feature in all the proximal femurs of the Krapina collection (six specimens recordable) and in 622 modern human adult femurs.

RESULTS

The feature consists in a series of crests delimitating three raised or depressed areas. This feature has been found in three out of four adult Neandertal femurs observable. The two observable subadult Neandertal femurs do not show this character. None of the modern femurs displayed the feature.

CONCLUSION

We interpret this feature as a muscular imprint, probably representing the m. vastus intermedius origin and discuss a possible interpretation. We did not find any other references for such imprint in the existing literature regarding the Neandertal femurs.

The Strength of Selection against Neanderthal Introgression

Hybridization between humans and Neanderthals has resulted in a low level of Neanderthal ancestry scattered across the genomes of many modern-day humans. After hybridization, on average, selection appears to have removed Neanderthal alleles from the human population. Quantifying the strength and causes of this selection against Neanderthal ancestry is key to understanding our relationship to Neanderthals and, more broadly, how populations remain distinct after secondary contact. Here, we develop a novel method for estimating the genome-wide average strength of selection and the density of selected sites using estimates of Neanderthal allele frequency along the genomes of modern-day humans. We confirm that East Asians had somewhat higher initial levels of Neanderthal ancestry than Europeans even after accounting for selection. We find that the bulk of purifying selection against Neanderthal ancestry is best understood as acting on many weakly deleterious alleles. We propose that the majority of these alleles were effectively neutral—and segregating at high frequency—in Neanderthals, but became selected against after entering human populations of much larger effective size. While individually of small effect, these alleles potentially imposed a heavy genetic load on the early-generation human–Neanderthal hybrids. This work suggests that differences in effective population size may play a far more important role in shaping levels of introgression than previously thought.

A small percentage of Neanderthal DNA is present in the genomes of many contemporary human populations due to hybridization tens of thousands of years ago. Much of this Neanderthal DNA appears to be deleterious in humans, and natural selection is acting to remove it. One hypothesis is that the underlying alleles were not deleterious in Neanderthals, but rather represent genetic incompatibilities that became deleterious only once they were introduced to the human population. If so, reproductive barriers must have evolved rapidly between Neanderthals and humans after their split. Here, we show that observed patterns of Neanderthal ancestry in modern humans can be explained simply as a consequence of the difference in effective population size between Neanderthals and humans. Specifically, we find that on average, selection against individual Neanderthal alleles is very weak. This is consistent with the idea that Neanderthals over time accumulated many weakly deleterious alleles that in their small population were effectively neutral. However, after introgressing into larger human populations, those alleles became exposed to purifying selection. Thus, rather than being the result of hybrid incompatibilities, differences between human and Neanderthal effective population sizes appear to have played a key role in shaping our present-day shared ancestry.

Unconstrained cranial evolution in Neandertals and modern humans compared to common chimpanzees

A variety of lines of evidence support the idea that neutral evolutionary processes (genetic drift, mutation) have been important in generating cranial differences between Neandertals and modern humans. But how do Neandertals and modern humans compare with other species? And how do these comparisons illuminate the evolutionary processes underlying cranial diversification? To address these questions, we used 27 standard cranial measurements collected on 2524 recent modern humans, 20 Neandertals and 237 common chimpanzees to estimate split times between Neandertals and modern humans, and between Pan troglodytes verus and two other subspecies of common chimpanzee. Consistent with a neutral divergence, the Neandertal versus modern human split-time estimates based on cranial measurements are similar to those based on DNA sequences. By contrast, the common chimpanzee cranial estimates are much lower than DNA-sequence estimates. Apparently, cranial evolution has been unconstrained in Neandertals and modern humans compared with common chimpanzees. Based on these and additional analyses, it appears that cranial differentiation in common chimpanzees has been restricted by stabilizing natural selection. Alternatively, this restriction could be due to genetic and/or developmental constraints on the amount of within-group variance (relative to effective population size) available for genetic drift to act on.

Neonatal postcrania from Mezmaiskaya, Russia, and Le Moustier, France, and the development of Neandertal body form

Neandertal and modern human adults differ in skeletal features of the cranium and postcranium, and it is clear that many of the cranial differences-although not all of them-are already present at the time of birth. We know less, however, about the developmental origins of the postcranial differences. Here, we address this deficiency with morphometric analyses of the postcrania of the two most complete Neandertal neonates-Mezmaiskaya 1 (from Russia) and Le Moustier 2 (from France)-and a recent human sample. We find that neonatal Neandertals already appear to possess the wide body, long pubis, and robust long bones of adult Neandertals. Taken together, current evidence indicates that skeletal differences between Neandertals and modern humans are largely established by the time of birth.

Climate-mediated shifts in Neandertal subsistence behaviors at Pech de l'Azé IV and Roc de Marsal (Dordogne Valley, France)

Neandertals disappeared from Europe just after 40,000 years ago. Some hypotheses ascribe this to numerous population crashes associated with glacial cycles in the late Pleistocene. The goal of this paper is to test the hypothesis that glacial periods stressed Neandertal populations. If cold climates stressed Neandertals, their subsistence behaviors may have changed-requiring intensified use of prey through more extensive nutrient extraction from faunal carcasses. To test this, an analysis of Neandertal butchering was conducted on medium sized bovid/cervid remains composed of predominately red deer (Cervus elaphus), reindeer (Rangifer tarandus), and roe deer (Capreolus caprelous) deposited during global warm and cold phases from two French sites: Pech de l'Azé IV (Pech IV, Bordes' excavation) and Roc de Marsal (RDM). Analysis of surface modification on high survival long bones and proximal and middle phalanges demonstrates that skeletal elements excavated from the cold levels (RDM Level 4, Pech IV Level I2) at each cave have more cut marks and percussion marks than elements from the warm levels (RDM Level 9, Pech IV Level Y-Z) after controlling for fragment size. At both sites, epiphyseal fragments are rare, and although this pattern can result from carnivore consumption, carnivore tooth marks are almost nonexistent (<0.1%). Alternatively, processing epiphyseal ends for bone grease may have been a Neandertal survival strategy, and epiphyses were more intensively percussed in cold levels than in warm levels at both RDM and Pech IV. The exploitation of low marrow yield elements such as phalanges does not show a consistent pattern relating to climate, but may have been a general Neandertal behavioral characteristic, suggesting that these hominids were regularly on the edge of sufficient nutrient availability even during interglacials. Overall, the faunal assemblages from Roc de Marsal and Pech IV provide some support for the hypothesis that Neandertals were processing faunal remains more heavily during glacial periods, suggesting a response to increased nutritional stress during colder time periods.