Natural selection and developmental sexual variation in the human pelvis

Area of Science:

• Human anatomy and evolutionary biology
• Developmental biology
• Bioanthropology

Background:

• The human pelvis undergoes significant changes from childhood to adulthood.
• Understanding these changes is crucial for comprehending sexual dimorphism and evolutionary pressures.
• Previous studies have focused on adult pelvic morphology, with less emphasis on developmental trajectories.

Purpose of the Study:

• To investigate ontological patterns of pelvic variation and growth from age 8 to 18.
• To identify regions of differential growth, growth canalization, and evidence of natural selection in the human pelvis.
• To compare methodologies for assessing selection pressures on pelvic dimensions.

Main Methods:

• Pelvic radiogrammetry data from the Fels Longitudinal Growth Study (180 8-year-olds, 89 18-year-olds).
• Comparison of coefficients of variation (CVs) and total growth increments between sexes and ages.
• Statistical analyses including Student's t-tests, Mann-Whitney U-test, and Sokal and Braumann methods for CV comparison.

Main Results:

• Significant sex differences in ischium and acetabular breadth observed at age 8.
• Most pelvic sexual dimorphism develops during adolescence, with distinct remodeling of the pelvic cavity.
• Males show greater acetabular growth; females show greater pelvic cavity growth.
• Stabilizing selection indicated by reduced variation in 7 pelvic dimensions; disruptive selection indicated by increased variation in 6 dimensions.

Conclusions:

• Pelvic sexual dimorphism is largely established during adolescent growth.
• Distinct growth patterns in males and females suggest differential adaptive pressures.
• Analysis of CVs over time provides a robust method for inferring selection on pelvic morphology.