Sexual dimorphism in directional asymmetry of the upper limb bones among Khoe-San skeletons

Sex differences in workload in medieval Poland: Patterns of asymmetry and biomechanical adaptation in the upper limb at Giecz

OBJECTIVES

This study characterizes sexual dimorphism in skeletal markers of upper limb mechanical loading due to lateralization as evidence of division of labor in medieval Giecz, Poland.

METHODS

Twenty-six dimensions for paired humeri, clavicles, and radii representing adult males (n = 89) and females (n = 53) were collected from a skeletal sample from the cemetery site Gz4. Percent directional asymmetry (DA) and absolute asymmetry (AA) for each dimension were compared among bones, osteometric subcategories, and sex. Additionally, side bias and sex differences were assessed in degenerative joint disease (DJD) and entheseal changes (ECs).

RESULTS

Nearly all measurements revealed significant asymmetry favoring the right side. Asymmetry was most pronounced in midshaft dimensions with few sex differences. There were more correlations among dimensions within elements than between elements, mainly in the midshaft. No laterality in DJD frequencies was noted for either sex, but females demonstrated significantly lower odds of having DJD than males in most joints. Most ECs demonstrated a right-bias and association with DA with no sex-specific patterns except the biceps brachii insertion, where females were ~5 times more likely to be scored "right" than males.

DISCUSSION

The general lack of sex differences in asymmetry and ECs suggests similarly demanding workloads for females and males, with the exception of sex-specific functional loading differences in the forearm. Further, DJD data suggest males engaged in more intensive activities involving the upper limb. These results enhance understanding of workload in this important historical period and provide a comparison for asymmetry in past populations.

The effects of hand preference and sex on right-left asymmetry in dorsal digit lengths among adults and children

BACKGROUND

Right-hand preference is related to stronger right-directional asymmetry in the length of proximal upper-limb bones, although the relationships of hand preference with directional asymmetry in phalangeal bone lengths are not known. Furthermore, dorsal digit length is an easy-to-measure, faithful proxy of X-rayed phalangeal bone length (which is costly and difficult to measure).

AIM

To study the effects of hand preference, sex, and age on right-left (R-L) asymmetry in dorsal digit lengths.

METHODS

We measured all dorsal digit lengths (except the thumb) in comparable numbers of left-handers and right-handers in samples of adults (N = 151, age: M = 22.6 years, SD = 3.3) and children (N = 65, age: M = 5.0 years, SD = 1.0).

RESULTS

Right-handers and adults had stronger right-directional asymmetry in digit lengths than left-handers and children. A Bayesian analysis yielded an 'extremely strong likelihood' of no sex differences in the R-L asymmetry of dorsal digit lengths 2 and 4.

CONCLUSIONS

The effects of hand preference, sex, and age on R-L asymmetry appear to be similar for phalangeal bone length and other (proximal) upper-limb bone lengths. Two distinct biologic mechanisms (i.e., a general right-directional asymmetry mechanism and a handedness-related directional asymmetry mechanism) may contribute to observed R-L asymmetry in limbs. Fingertip fat and bone digit length do not seem to contribute to sex differences in the R-L asymmetry (Dr-l) of the widely studied second-to-fourth digit ratio (2D:4D).

Gendered division of labor in a Celtic community? A comparison of sex differences in entheseal changes and long bone shape and robusticity in the pre-Roman population of Verona (Italy, third-first century BC)

OBJECTIVES

The presence of a gendered subdivision of labor has been bioarchaeologically investigated in various prehistoric and historical contexts. Little is known, however, about the type of differences in daily activities characterizing men and women among the Celtic communities of Italy. The focus of the present study is the analysis of differences in patterns of entheseal changes (ECs) and long bone shape and robusticity between sexes among the Cenomani Gauls of Seminario Vescovile (SV-Verona, Italy, third-first century BC).

MATERIALS AND METHODS

The sample includes 56 adult individuals (22 females and 34 males). Presence of ECs on nine bilateral postcranial attachment sites, and values of humeral and femoral shape and robusticity indices based on external measurements were compared between sexes by means of generalized linear models and Mann-Whitney tests.

RESULTS

Results show a lack of difference between sexes in long bone shape and robusticity, and a higher incidence of upper and, especially, lower limb ECs in males.

DISCUSSION

These results suggest the presence of sex-specific activities at SV mostly related to farming and differently influencing the considered variables. Also, this study suggests the relevance of a series of nonbiomechanical factors (developmental, hormonal, genetic, and methodological) when attempting biocultural reconstructions from osteoarchaeological samples.

Asymmetry patterns are associated with body size and somatic robustness among adult !Kung San and Kavango people

Asymmetry of bilateral anatomical structures is widely found in nature. Fluctuating asymmetry, i.e. mostly tiny random deviations from perfect symmetry in bilateral structures, is mainly interpreted within the framework of developmental instability. This interpretation is mainly due to the fact, that higher fluctuating asymmetry is often found in association with various pathological conditions but also from increased stress during somatic development. Directional asymmetry, in contrast, describes a distinct pattern of bilateral variation in a group of individuals, characterized by the tendency to find the larger side mainly at the same side for all individuals. This kind of asymmetry is mostly caused by behavioral lateralization. Somatic stress during development affect not only asymmetry patterns, it is has also an adverse effect on somatic growth. Therefore, the present study tested the hypothesis, that increased asymmetry is associated with decreased body height as well as postcranial length and robustness dimensions. The association patterns between fluctuating as well as directional asymmetry and parameters of somatic growth and robustness are analyzed among 236 !Kung San and 248 Kavango people of Namibia between the ages of 18 and 65 years. Fluctuating asymmetry was determined by ear length and ear breadth. Directional asymmetry was determined by hand length and hand breadth dimensions. Fluctuating as well as directional asymmetry correlated significantly negatively with body height and length dimensions, the correlations however, were weak. The results are interpreted as a corroboration of the theory that developmental stress may increase fluctuating asymmetry but on the other hand may decrease body size.

External ballistics of Pleistocene hand-thrown spears: experimental performance data and implications for human evolution

The appearance of weaponry - technology designed to kill - is a critical but poorly established threshold in human evolution. It is an important behavioural marker representing evolutionary changes in ecology, cognition, language and social behaviours. While the earliest weapons are often considered to be hand-held and consequently short-ranged, the subsequent appearance of distance weapons is a crucial development. Projectiles are seen as an improvement over contact weapons, and are considered by some to have originated only with our own species in the Middle Stone Age and Upper Palaeolithic. Despite the importance of distance weapons in the emergence of full behavioral modernity, systematic experimentation using trained throwers to evaluate the ballistics of thrown spears during flight and at impact is lacking. This paper addresses this by presenting results from a trial of trained javelin athletes, providing new estimates for key performance parameters. Overlaps in distances and impact energies between hand-thrown spears and spearthrowers are evidenced, and skill emerges as a significant factor in successful use. The results show that distance hunting was likely within the repertoire of hunting strategies of Neanderthals, and the resulting behavioural flexibility closely mirrors that of our own species.

Forensic and Anthropological Application of Body Asymmetry: A Comment on Gutnik et al. (2015)

The present communication describes the application of bilateral asymmetry in forensic casework and anthropological research. Bilateral asymmetry is normal in the human body. The body’s asymmetry is attributable to genetic and environmental (evolutionary) reasons. Handedness is a factor related to bilateral asymmetry. Gutnik et al. (2015) supported previous research, showing that the dominant side of the body is stronger than the other side due to additional stress and strain, and thus has augmented musculature and increased mass. The note is intended to elaborate on the applications of body asymmetry in forensic and anthropological practice.