The relationship between bipedalism and growth: A metric assessment in a documented modern skeletal collection (Certosa Collection, Bologna, Italy)

Abstract

Objectives: Long bone variations during growth are susceptible to the combined action of nutritional, hormonal, and genetic factors that may modulate the mechanical forces acting upon growing individuals as they progressively acquire a mature gait.In this work, we explore diaphyseal length and breadth variations of tibia and fibula during ontogeny (a) to test the presence of changes in relation to early toddling, and (b) to further our understanding of developmental patterns in relation to sex. Materials and Methods: Lengths, breadths, and indices were analyzed on right and left leg bones of 68 subadult individuals (Human Identified Skeletal Collection of the University of Bologna, Italy). Analyses included intersex and age classes (1, 0-1 year; 2, 1.1-3 years; 3, 3.1-6 years) comparisons, linear regressions with age and assessment of correlation among tibial and fibular measurements, as well as principal component analysis. Results: A significant difference emerged among age class 1 and the others. Age class 1 and 3 differ between them, while age class 2 overlaps with the others. No sex dimorphism was detected. All measurements were strongly correlated with age. Tibial and fibular measurements correlated with each other. Conclusions: Our results relate the progressive emergence of toddling attempts in growing individuals at the end of the first year of age. No significant sex differences

Sexual Dimorphism in the Fibular Extremities of Italians and South Africans of Identified Modern Human Skeletal Collections: A Geometric Morphometric Approach

“…According to our results, fibulae of males possess larger linear dimensions than females, due to a generally larger body size (regardless of body mass), possibly due to a relatively longer pubertal growth period, and the subsequent development of larger bones and muscles under the influence of sex genes, sex steroids (androgens and estrogens), and other hormones, such as growth hormone (GF) and insulin-like growth factor 1 (IGF1) which, concurring with mechanical loading, may further contribute to the development of skeletal sexual dimorphism [80][81][82]. Indeed, bone growth is differentiated between sex groups, mostly evident during puberty but to a lesser extent also apparent in early childhood [83][84][85], and this concurs with the observed greater cortical bone plasticity in males, modelled by greater muscle mass during ontogeny, determining greater long bone lengths and breadths, also already observed for the fibula in a similar sample [86]. During puberty, males develop higher peak bone mass, greater bone size, and, ultimately, a stronger skeleton than females [87,88], with different skeletal maturation timing for both fibular extremities according to sex [55].…”

Entheseal variation and locomotor behavior during growth

“…Age class 2 (1–5.9 years): Bipedal locomotion is present but still immature (toddling). This is therefore a long transitory phase that goes from a rudimental and still dependent locomotion to a mature gait (Adolph et al., 2003; Cowgill et al., 2010; Forssberg, 1985; Hallemans et al., 2003, 2004, 2006a, 2006b; Ivanenko et al., 2004; McGraw, 1940; Pietrobelli, Marchi, & Belcastro, 2022; Swan et al., 2020; Zeininger et al., 2018). Age class 3 (6–10.9 years), 4 (11–15.9 years), 5 (16–20.9 years), 6 (21–25.9 years), 7 (26–30 years): Even though from the age of 6, a bipedal gait is already completely acquired, the remaining individuals have also been divided into quinquennial classes (except for the last one which covers 4 years) to identify any possible morphological changes in entheses in relation to bone lengthening (classes 3–5) and entheseal “settlement” once the definitive stature has been reached (classes 6–7).…”

“…Our work is aimed at investigating the entheseal morphometric variability of the femoral insertion of gluteus maximus (hereinafter "GM") and tibial origin of soleus (hereinafter "SOL") muscles (already studied in the Neanderthal samples) in juvenile individuals in relation to age, sex and locomotor pattern during growth, adding new insights on the biological and biomechanical aspects of bipedalism, from an ontogenetic and evolutionary point of view, already explored in our research group also with other approaches (Sorrentino et al, 2020a, 2020b, 2020c, Figus et al, 2022Pietrobelli et al, 2022aPietrobelli et al, , 2022bPietrobelli et al, , 2023Colombo et al, 2019). In detail, we developed a recording standard method to better classify the entheseal (continuous) variability into discrete classes and verify its applicability in response to the locomotor pattern (detailed below).…”

Scientific and Ethical Aspects of Identified Skeletal Series: The Case of the Documented Human Osteological Collections of the University of Bologna (Northern Italy)

“…These collections have been the subject of a large body of research focused on various topics. The latter include methodological studies focused on estimation of age-at-death and attribution of sex [47][48][49][50][51][52][53][54][55][56][57][58][59][60][61], the study of entheseal changes in modern humans [62][63][64][65][66][67], and the discussion of their variability among extinct taxa [1][2][3][4]. Additional topics of investigation have been the various expression and demographic distribution of skeletal morphological variants and pathological changes [68][69][70][71], as well as dental and palate traits [72][73][74][75][76].…”

“…Similarly, anthropological methods of forensic relevance are continuously being developed and implemented on the DHOC of the University of Bologna. Age estimation methods built upon biological data of the osteological collections encompass a technique based on the observations of the timing of fusion of secondary ossification centers of the postcranium [47,48,51,54,55], morphological aspects of the os coxae [52,53], and dental features such as the pulp/tooth ratio among canine teeth [49,50] for adults, while diaphyseal linear growth was documented for the leg in subadults [61]. Sex attribution methods were developed with the aid of three-dimensional morphometrics considering the adult morphology of the human cranium and ankle [56,57,80,81,84].…”