The Universal Model of Growth: Dependence of Brain and Body Mass on Age

OBJECTIVES: To test whether the universal two-parameter DS model, originally proposed in 2015, can accurately describe how human brain and body mass change from conception to old age and reproduce their complex allometric relationship. METHODS: We analyzed published autopsy data on brain and body mass from conception to ~90 years, encompassing both sexes. Using nonlinear least-squares regression in Maple, we fitted the DS model to the data, testing single- and two-stage growth scenarios. Model performance was evaluated via residual analysis. RESULTS: A two-stage model-with a transition at ~1.5 years post-conception-accurately described both brain and body mass trajectories (typically within 10% error). The model successfully reproduced the non-monotonic, "hook-shaped" allometric curve of brain vs. body mass, including age-related declines after ~45 years. Furthermore, rescaling age using development time (derived from the DS model) largely eliminated sex differences in body mass trajectories and equalized male and female life expectancy in biological time. CONCLUSIONS: The DS model provides a parsimonious, scientifically well-grounded framework for human ontogenetic growth. It identifies ~1.5 years post-conception as a critical developmental transition and offers a physiologically meaningful time metric with potential applications in theoretical biology, evolutionary anthropology, biogerontology, etc.