A model of developmental canalization, applied to human cranial form

Area of Science:

• Developmental biology
• Evolutionary biology
• Biostatistics

Background:

• Developmental canalization, the process by which organisms buffer against perturbations during development, is essential for individual health and the evolution of complex life.
• The precise mechanisms and genetic encoding of developmental trajectories remain largely unknown, with debate on whether they are predetermined or emergent phenomena.

Purpose of the Study:

• To develop a statistical model for estimating developmental canalization from longitudinal phenotypic data.
• To investigate the presence and strength of canalization in human craniofacial development, including size and shape, and frontal sinus size.

Main Methods:

• An extended autoregressive statistical model was developed to quantify developmental canalization.
• Longitudinal geometric morphometric data of human postnatal craniofacial size and shape, along with frontal sinus size, were analyzed.

Main Results:

• Craniofacial size exhibited strong canalization during the first five years of life, reducing variance by 50%, with increased variance during puberty.
• Frontal sinus size showed no significant canalization, while craniofacial shape variance initially decreased then increased.
• Specific craniofacial features displayed varied canalization patterns; nasopharynx dimensions were strongly canalized, whereas facial orientation variance increased over time.

Conclusions:

• The study provides a statistical framework for analyzing developmental canalization, even without direct observation of target trajectories.
• Human craniofacial development involves evolved, partly mechanically induced canalization mechanisms, particularly for ensuring proper upper airway and facial dimensions.
• Differential canalization patterns highlight the complexity of developmental processes and their role in shaping organismal form.