A quantitative genetic approach to study the ontogeny and evolution of ecogeographic patterns in the human limb skeleton

Understanding the underlying causes of phenotypic variation in modern humans is an important topic in biological anthropology. There is a great amount of diversity in the geographic distribution of human limb morphology (shape, dimensions, and proportions). This dissertation seeks to understand how evolution has shaped this diversity in the human limb skeleton through changes in growth and development (ontogeny). Past studies showed that adaptation by natural selection to climate, neutral (non-selective) evolution, and nonheritable change in response to climate (phenotypic plasticity) may all play important roles in shaping the diverse patterns in the human limb skeleton. In addition, studies on juvenile skeletons showed there are distinguishable differences in limb morphology between populations at an early age. This project uses a quantitative genetic approach to test hypotheses about how different evolutionary forces influence the diversity in the human limb skeleton. In the past, studies that used a quantitative genetic approach to answer biological anthropology questions often made assumptions in order to facilitate statistical testing. The first part of this dissertation tests one of the central assumptions in quantitative genetics: that the genetic variance-covariance (V/CV) matrix (G) is proportional to the phenotypic V/CV matrix (P). Results suggest even a perfectly sampled P can produce drastically different results from a well-estimated G for some evolutionary statistics. The second part of this dissertation tests whether allometric relationships between body mass and skeletal traits are conserved among different groups and across different age stages. Using a contemporary Taiwanese sample, I evaluated body mass estimation equations for children and juvenile individuals developed using a European American sample based on the principles of allometry. Results show current methods provided good body mass estimates in Taiwanese individuals, with accuracy and bias similar to those reported in other validation studies. This suggests the relationship between overall body size and various skeletal traits represented by linear measurements will be conserved among different groups and across age. The final part of this dissertation builds a linear mixed-effects model to study the ontogenetic trajectories of the dimensions of the limb skeleton. Using a global sample of osteometric measurements of both archaeological and contemporary groups, climatic variables, and genomic data to infer group relationships, I partitioned the effects of both neural (non-selective) and climatic factors on human limb dimensions during growth. The results show population structure arising from neutral evolution, the allometric variation associated with the change in size, and directional effects from climatic factors all contributed to the variation in ontogenetic trajectories of all major long bone dimensions in modern humans. There is a clear, albeit weak, trend of association with extreme temperatures that fits the predictions of ecogeographic rules, indicating ecogeographic patterns exist throughout ontogeny, after accounting for the effects of neutral evolution. This work is the first to directly study the relationship between different evolutionary forces and variation in ontogenetic trajectories. The results have implications in evolutionary biology as well as different subfields of biological anthropology.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Anthropology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2021

Author dc:creator

• Yim, An-Di

Contributors dc:contributor

• Roseman, Charles C
• Konigsberg, Lyle W
• Shackelford, Laura
• Cowgill, Libby
• Weaver, Timothy

• Quantitative genetics
• Allometry
• Growth and development
• Ecogeographic patterns
• Human variation

Statement dc:rights

• Copyright 2021 An-Di Yim

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/110700

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/110700