Late Pleistocene human femoral diaphyseal curvature

Abstract

Anterior femoral curvature is a consistent characteristic of Pleistocene and recent humans, although variation exists in the degree of curvature among individuals and across populations. In particular, one group, the Neandertals, has been characterized for a century as having marked femoral curvature. To evaluate the degree of anterior femoral curvature in both Neandertals and other Late Pleistocene humans, their curvature subtenses and proximodistal positions were evaluated in the context of recent human variation. Recent human comparisons show little relationship between subtense (absolute curvature) and femoral length, suggesting that an index that incorporates subtense relative to the length of the femur is inappropriate for between-group assessments. Neandertals were statistically indistinguishable from Middle or earlier Upper Paleolithic modern humans in the degree of absolute curvature, all of whom had greater curvature on average than all later humans. Additionally, Neandertals and Qafzeh-Skhul early modern humans had a more distal point of maximum curvature than any other group. Curvature was not strongly correlated with functional considerations including body mass estimates, surrogate variables for body size, proximal femoral articular orientation, or knee anteroposterior dimensions. The functional role of femoral anterior curvature is unknown; however, the general decrease in curvature subtense closely parallels the between-group changes in inferred levels of mobility from femoral diaphyseal robusticity and shape, suggesting that femoral curvature may reflect mobility levels and patterns among Late Pleistocene and recent humans.

The shape of the Neandertal femur is primarily the consequence of a hyperpolar body form

“…However, contrasts between Neandertals and near-modern humans in the cross-sectional shape of the femoral shaft also seem to be the mechanical consequence of body proportions (12). Moreover, although shaft bowing is often cited as an exclusive feature of the Neandertal femur, when this feature is quantified, Neandertals are not statistically distinguishable from their contemporaries (30). Therefore, the results of this study combined with other studies (12)(13)(14)(18)(19)(20) show that most if not all clear contrasts in shape between the femora of Neandertals and near-modern humans seem to be secondary consequences of differences in climate-induced body proportions.…”

Technical note: A new method for measuring long bone curvature using 3D landmarks and semi‐landmarks

“…2. Methods that assess the magnitude and position of the maximum subtense as measured from the anterior diaphyseal surface to the chord, which connects the proximal and distal anterior femoral concavities (Shackelford and Trinkaus, 2002). 3.…”

“…Femoral curvature, for example, varies widely and has been used as a means to differentiate among recent human populations as well as between Neanderthals and anatomically modern humans (e.g. Ried, 1924;Stewart, 1962;Walensky, 1962Walensky, , 1965Gilbert, 1976;Trudell, 1999;Shackelford and Trinkaus, 2002).Curvature in long bones is not a uniquely human feature and is common in terrestrial mammals. Studies on several mammals such as horses, sheep, and a variety of anthropoid species, have investigated the properties of longitudinal diaphyseal curvature and how it may affect the biomechanical properties of the bone and bone function (Frost, 1967;Lanyon and Baggott, 1976;Lanyon and Bourn, 1979;Swartz, 1990;Les et al, 1997;Lieberman and Pearson, 2001;Shackelford and Trinkaus, 2002;Richmond, 2003).…”

“…Ried, 1924;Stewart, 1962;Walensky, 1962Walensky, , 1965Gilbert, 1976;Trudell, 1999;Shackelford and Trinkaus, 2002).…”

“…In experimental work with rats, Lanyon (1980) concluded that there are certain features of long bones that are genetically determined, like length, but that other features such as curvature are dependent on normal weight bearing and muscle activity during growth. This normal mechanical environment shapes the bone to its function and emphasizes the need to include muscle activity when modeling the biomechanical properties of the femur (Lanyon and Baggott, 1976;Lanyon and Bourn, 1979).The biomechanical role and adaptive benefits of an increase in magnitude of curvature is not straightforward and may vary between limb segments and across species (Shackelford and Trinkaus, 2002). Several hypotheses have been proposed.…”