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

The two-stage DS model accurately described both brain and body mass trajectories from conception to approximately 90 years.

• The model fit was 'typically within 10% error' for both brain and body mass trajectories.
• Data encompassed both sexes from conception to ~90 years of age.
• Autopsy data from published sources were analyzed using nonlinear least-squares regression in Maple.
• Both single- and two-stage growth scenarios were tested, with the two-stage model outperforming the single-stage scenario.

A critical developmental transition occurs at approximately 1.5 years post-conception.

• The two-stage model identified ~1.5 years post-conception as the transition point between growth stages.
• This transition was identified for both brain and body mass trajectories.
• The DS model is described as a 'two-parameter' model originally proposed in 2015.

The DS model successfully reproduced the non-monotonic, 'hook-shaped' allometric curve of brain versus body mass.

• The allometric relationship between brain and body mass is described as 'non-monotonic' and 'hook-shaped'.
• The model reproduced age-related declines in brain mass after approximately 45 years.
• This complex allometric relationship was captured using the same two-parameter framework applied to individual growth trajectories.

Rescaling age using the development time derived from the DS model largely eliminated sex differences in body mass trajectories.

• When biological time (derived from the DS model's development time parameter) was used instead of chronological age, sex differences in body mass trajectories were largely removed.
• Rescaling also equalized male and female life expectancy when expressed in biological time.
• This finding suggests that observed sex differences in growth and longevity may reflect differences in developmental pace rather than fundamental biological differences.

The DS model is presented as a parsimonious, two-parameter framework for describing human ontogenetic growth from conception to old age.

• The model was originally proposed in 2015 and is described as 'universal' and 'scientifically well-grounded'.
• The model uses only two parameters to describe growth trajectories.
• Potential applications include theoretical biology, evolutionary anthropology, and biogerontology.
• The development time derived from the model provides 'a physiologically meaningful time metric'.