Evolvability in human postcranial traits across ecogeographic regions

Abstract

Objectives: Though recent quantitative genetic analyses have indicated that directional selection appears to be acting on limb lengths and measures of body size in modern humans, these studies assume equal evolvability across modern human groups. However, differences in trait covariance structure due to ancient migration patterns and/or selection may limit the evolvability of populations further from Africa. This study therefore explores patterns of human evolvability across ecogeographic regions. Materials and Methods: Mean evolvability, respondability, conditional evolvability, and autonomy were calculated from variance-covariance matrices of limb length and body size measures representing 14 human groups spanning four ecogeographic regions. Measures of evolvability were compared across groups and regions, and the minimum sample size, inaccuracy, and bias were calculated for each. Results: When compared between regions, humans demonstrate significant differences between indices of evolvability across regions. Despite the relatively recent evolution of modern humans, several measures of evolvability show a strong negative correlation with latitude across regions, demonstrating a reduction in genetic variance that is potentially reflective of human migration and/or response to selection.Conclusions: These results demonstrate the importance of establishing patterns of evolvability prior to additional quantitative genetic analyses, and emphasize the influence of sample size on the accuracy of estimated evolvability measures. These findings also suggest that while modern human groups share similar covariance structures, there is evidence for emergent differentiation in evolvability and respondability between human groups across ecogeographic regions, further complicating our ability to apply results derived from modern human groups to ancient hominin lineages.

Mixed models for the relationship between latitude, temperature, and human postcranial form

“…The results of the mixed‐effects models both corroborate previous findings as well as contribute information and nuance to understanding the evolution of limb lengths and body size among humans. The latitude and minimum temperature mixed‐effects models indicate that natural selection was responsible for some trait evolution, especially in measures of body size, which further supports studies that have used different evolutionary models to arrive at the same conclusion (Betti et al, 2012; Roseman & Auerbach, 2015; Savell, 2020; Savell et al, 2016). By approaching the evolutionary model with fixed effects of latitude and temperature variables, however, this study demonstrates that these variables may not have contributed as much to selection across body proportion traits as previously suspected, and that we may have underestimated the role of stabilizing selection, population history, neutral evolutionary processes, and covariance in the evolution of these measures.…”

“…If decades of prior research equating human morphological variation with global patterns of climate are supported, we expect to find evidence that climatic variables and latitude both present the best models to explain variation in limb length and measures of body mass, and that this variation is best explained by models representing response to directional natural selection. Previous studies (Savell, 2020; Savell et al, 2016) demonstrated that long bone lengths form a distinct integrated set from dimensions associated with body size and breadth, and so we also expect these two integrated groups to exhibit independent relationships with both responses to selection in climate or latitude as well as population structure.…”

“…This study was an attempt to disentangle the effects of latitude from those of temperature on the evolution of human body size and limb proportions under the thermoregulatory imperative model (Ruff, 1994). Recent quantitative genetic studies (Roseman & Auerbach, 2015; Savell, 2020; Savell et al, 2016) suggest that distal limb lengths and measures of body size have evolved at least partially in response to directional selection, though the global variation in these traits reflects a combination of the effects of selection and population structure (cf. Betti et al, 2012).…”

“…Recent quantitative genetic studies (Roseman & Auerbach, 2015;Savell, 2020;Savell et al, 2016) suggest that distal limb lengths and measures of body size have evolved at least partially in response to directional selection, though the global variation in these traits reflects a combination of the effects of selection and population structure (cf. Betti et al, 2012).…”

Evolvability in the fossil record

“…This assumes that the estimated P or G from the extant population is similar enough to G in the ancestral, extinct population. Based on similarities between closely related extant species, a wide array of work (both neontological and paleontological) has assumed that P (or G ) from an extant population is representative of the ancestral G , which has allowed researchers to make evolutionary inferences from phenotypic data across macroevolutionary timescales in ways that would otherwise be impossible (Ackermann and Cheverud 2004; de Oliveira et al 2009; Rolian 2009; Marroig and Cheverud 2010; Young et al 2010; Grabowski et al 2011; Grabowski 2013; Baab 2018; Villamil 2018; Savell 2020; Agosto and Auerbach 2021).…”