38 - Morphological Integration and Evolutionary Potential Among the Human Basicranium, Limb Girdles, and Limb Segments

Poster Board Number: 38
There are separate poster presentation times for odd and even posters.
Odd poster #s – first hour
Even poster #s – second hour

Abstract Body : Morphological evolution is a whole-organism phenomenon, as the underlying functional, developmental, and genetic covariances among traits may constrain their ability to independently respond to the force of directional selection. Through the application of evolutionary quantitative genetics, researchers have been able to explore evolutionary potential across anatomical regions, especially among those previously thought to evolve independently. Agosto and Auerbach (Journal of Human Evolution, 2022) investigated such relationships among the basicranium, limb girdles, and humerus in a sample of eight primate taxa, including humans, and reported evidence of potential genetic constraint among the basicranium and limb girdles. While these regions experience mutual evolutionary constraint, it is unknown how these relationships may relate to the upper and lower limbs, which previous research has shown are not genetically independent. In this study, we investigate potential evolutionary relationships between the limb girdles and limb segments, as well as the basicranium in humans.

Here, we evaluate the strength of the genetic covariance and evolutionary potential between seven anatomical regions: basicranium, shoulder girdle, pelvic girdle, arm, forearm, thigh, and leg. We obtained linear cranial and postcranial dimensions from a sample of 104 modern humans (55 female, 49 male). All covariance matrices were size corrected prior to all analyses. We estimated morphological integration using Wagner’s variance of the eigenvalues, and estimated evolutionary potential using Hansen and Houle’s indices of conditional and unconditional evolvability with 1000 simulated random selection gradients. Analyses were performed using the R statistical environment.

Our results both parallel and further clarify previous findings of evolutionary potential in humans. As previously reported, evolutionary relationships between the basicranium and limb girdles show there is greater evolutionary constraint between the basicranium and shoulder girdle compared to the basicranium and pelvic girdle, or between the shoulder and pelvic girdles. Novel results demonstrate evolutionary constraint between the limb segments and basicranium as being the second strongest among pairings of the anatomical regions evaluated. This degree of constraint is unexpected given that these regions have different genetic networks underlying their development and lack direct functional relationships, as well as low integration as shown by our results. These results reinforce the existence of potential evolutionary relationships among anatomical regions that are traditionally treated as independent, which has important implications for models of primate evolution.