Hafted technologies likely reduced stone tool-related selective pressures acting on the hominin hand

The evolution of the hominin hand has been widely linked to the use and production of flaked stone tool technologies. After the earliest handheld flake tools emerged, shifts in hominin hand anatomy allowing for greater force during precision gripping and ease when manipulating objects in-hand are observed in the fossil record. Previous research has demonstrated how biometric traits, such as hand and digit lengths and precision grip strength, impact functional performance and ergonomic relationships when using flake and core technologies. These studies are consistent with the idea that evolutionary selective pressures would have favoured individuals better able to efficiently and effectively produce and use flaked stone tools. After the advent of composite technologies during the Middle Stone Age and Middle Palaeolithic, fossil evidence reveals differences in hand anatomy between populations, but there is minimal evidence for an increase in precision gripping capabilities. Furthermore, there is little research investigating the selective pressures, if any, impacting manual anatomy after the introduction of hafted composite stone technologies ('handles'). Here we investigated the possible influence of tool-user biometric variation on the functional performance of 420 hafted Clovis knife replicas. Our results suggest there to be no statistical relationships between biometric variables and cutting performance. Therefore, we argue that the advent of hafted stone technologies may have acted as a 'performance equaliser' within populations and removed (or reduced) selective pressures favouring forceful precision gripping capabilities, which in turn could have increased the relative importance of cultural evolutionary selective pressures in the determination of a stone tool's performance.

A pathological Neandertal thumb phalanx from Moula-Guercy (France)

OBJECTIVE

To discuss a Neandertal pathological adult first pollical proximal phalanx (I2-104) from the Baume de Moula-Guercy (Ardèche, France) and evaluate the possible causes of this pathology.

METHODS

Macroscopic analyses of external features, as well as CT imaging, were used in the analysis RESULTS: The presence of asymmetric eburnation on the distal epiphysis associated with an osteophyte on the palmar surface, as well as the absence of periosteal bone reaction visible on CT images, is consistent with osteoarthritis.

CONCLUSION

Osteoarthritis (OA) can have different origins and the cause is difficult to identify. The pathology of the Moula-Guercy I2-104 phalanx may be due to a genetic predisposition for OA known in Neandertals and associated with short limb bones. The OA could have been aggravated by the age of this individual and by an inflammatory reaction caused by repeated movements and intense vibrations provoked by high-frequency knapping or by other use of the hands SIGNIFICANCE: The I2-104 phalanx is the first Neandertal pollical phalanx known to display OA, although joints of this bone are frequently affected by this pathology in modern humans. Thus, greater insight into the presence and consequences of Neandertal behaviors is offered LIMITATION: It is impossible to give a definitive conclusion on the cause(s) of the OA in this case.

SUGGESTIONS FOR FURTHER RESEARCH

More data is needed concerning OA within Neandertals and its relationship with behavior and genetics.

Neanderthal cranial remains from Baume Moula-Guercy (Soyons, Ardèche, France)

OBJECTIVES

We provide the first comparative description of the Guercy 1 cranium and isolated cranial fragments from Baume Moula-Guercy and examine their affinities to European Preneanderthals, Neanderthals, and Homo sapiens.

MATERIALS AND METHODS

The Moula-Guercy hominins derive from deposits chronostratigraphically and biostratigraphically dated to the Eemian Interglacial (MIS 5e). For comparisons we compiled a sample of European and Southwest Asian subadult-adult Middle-to-Late Pleistocene hominins (≈MIS 14-MIS 2; N = 184). This sample represents a Preneanderthal-Neanderthal group and a H. sapiens group, both of which were further divided into three time-successive subgroups defined by associated marine isotope stages (MIS). Metric and morphological observations were made on the original fossils and a virtual reconstruction of Guercy 1. Developmental age and sex and the minimum-maximum number of individuals were assessed.

RESULTS

Guercy 1 represents the remains of a late stage adolescent (≈15-16.0 years) female. Morphological and metric data combine to associate the total morphological pattern expressed in Guercy 1 with our MIS 7-MIS 5e ("Early Neanderthal") subgroup. Some features, especially those related to the frontal, suggest linkage to a paleodeme comprising the Moula-Guercy, Artenac, La Chaise Abri Suard and, possibly, the Biache-Saint-Vaast samples.

DISCUSSION

Remains of MIS 7-MIS 5e Neanderthals are rare and fragmentary, especially those dated to the Last Interglacial. The Baume Moula-Guercy sample provides new insights into the total morphological pattern expressed in MIS 5e Neanderthals. Further, our results support earlier suggestions that MIS 7-MIS 5e European hominins represent a morphotype that is distinct from both earlier and later members of the Preneanderthal-Neanderthal group.

Morphology of the Denisovan phalanx closer to modern humans than to Neanderthals

A fully sequenced high-quality genome has revealed in 2010 the existence of a human population in Asia, the Denisovans, related to and contemporaneous with Neanderthals. Only five skeletal remains are known from Denisovans, mostly molars; the proximal fragment of a fifth finger phalanx used to generate the genome, however, was too incomplete to yield useful morphological information. Here, we demonstrate through ancient DNA analysis that a distal fragment of a fifth finger phalanx from the Denisova Cave is the larger, missing part of this phalanx. Our morphometric analysis shows that its dimensions and shape are within the variability of Homo sapiens and distinct from the Neanderthal fifth finger phalanges. Thus, unlike Denisovan molars, which display archaic characteristics not found in modern humans, the only morphologically informative Denisovan postcranial bone identified to date is suggested here to be plesiomorphic and shared between Denisovans and modern humans.

The influence of digit size and proportions on dexterity during cold exposure

OBJECTIVES

The current study investigated whether size and proportions of the hands and digits affect dexterity during severe cold exposure. As wide hands are known to lose less heat than narrow hands, and narrow digits are associated with greater dexterity, this study aimed to test whether there was a direct trade-off between dexterity and thermoregulation that shapes hand morphology.

METHODS

Participants (25 women, 15 men) carried out the Purdue Pegboard test before and after a 3-min ice-water immersion of the hand. Their hand length, hand width, digit lengths, and digit widths were measured using standard anthropometric methods.

RESULTS

Wide first and third digits associated with significantly reduced dexterity after immersion relative to individuals with narrower first and third digits. Second digit width positively correlated with average digit temperature after immersion. Hand length and hand width did not influence dexterity.

CONCLUSION

The current study suggests that digit width influences dexterity in cold conditions, reflecting patterns found at room temperature. Hand and digit morphology may be the product of two significant constraints on the hand: dexterity and thermoregulation. In cold conditions, hand morphology appears to be predominantly constrained by thermal stress, at the expense of dexterity. This may have important implications for interpreting the morphology of extinct and extant hominins.

New Neandertal wrist bones from El Sidrón, Spain (1994-2009)

Twenty-nine carpal bones of Homo neanderthalensis have been recovered from the site of El Sidrón (Asturias, Spain) during excavations between 1994 and 2009, alongside ∼2500 other Neandertal skeletal elements dated to ∼49,000 years ago. All bones of the wrist are represented, including adult scaphoids (n = 6), lunates (n = 2), triquetra (n = 4), pisiforms (n = 2), trapezia (n = 2), trapezoids (n = 5), capitates (n = 5), and hamates (n = 2), as well as one fragmentary and possibly juvenile scaphoid. Several of these carpals appear to belong to the complete right wrist of a single individual. Here we provide qualitative and quantitative morphological descriptions of these carpals, within a comparative context of other European and Near Eastern Neandertals, early and recent Homo sapiens, and other fossil hominins, including Homo antecessor, Homo naledi, and australopiths. Overall, the El Sidrón carpals show characteristics that typically distinguish Neandertals from H. sapiens, such as a relatively flat first metacarpal facet on the trapezium and a more laterally oriented second metacarpal facet on the capitate. However, there are some distinctive features of the El Sidrón carpals compared with most other Neandertals. For example, the tubercle of the trapezium is small with limited projection, while the scaphoid tubercle and hamate hamulus are among the largest seen in other Neandertals. Furthermore, three of the six adult scaphoids show a distinctive os-centrale portion, while another is a bipartite scaphoid with a truncated tubercle. The high frequency of rare carpal morphologies supports other evidence of a close genetic relationship among the Neandertals found at El Sidrón.

The evolution of the hominin thumb and the influence exerted by the non-dominant hand during stone tool production

Modern humans possess a highly derived thumb that is substantially stronger and more robust than the fingers. Previous hypotheses concerning the evolution of such traits have focused upon the manipulation of hammerstones during stone tool production and of stone tools during their use. To date there has been no research on the manipulative pressures exerted by the non-dominant (core-holding) hand during stone tool production and its potential influence on the evolutionary history of the thumb. Here we provide the first investigation into the frequencies of digit recruitment and the relative manipulative forces experienced in the non-dominant hand during stone tool production. Eight experienced knappers produced flake cutting tools under four distinct conditions while pressure sensors, secured to the volar pads of the thumb, index and middle fingers of the non-dominant hand, recorded manipulative forces. Results indicate that relative to the fingers, the thumb was recruited significantly more frequently and experienced significantly greater manipulative forces during core repositioning events and the securing of the core during flake detachments. Our results support the hypothesis that the robust thumb anatomy observed in the hominin lineage was selected for, at least in part, as a result of more frequent and greater manipulative pressures acting upon the thumb relative to the fingers on the non-dominant hand during stone tool production.