Human growth from the cell to the organism: saltations and integrative physiology.

The Society for the Study of Human Biology has been at the forefront in the scientific study of human growth. The documentation of variability in growth rate, size, and tempo across populations has provoked exploration for sources of this diversity, and the mechanisms by which environmental and genetic factors influence phenotypic expressions of growth biology. At a time when adult health and well-being are posited to reflect early development, the details of early growth patterns are increasingly sought as explanatory domains underlying lifespan health. A review of recent observations detailing events that occur in growth and differentiation during embryological and fetal development is considered for insights into mechanisms that may be operative in a putative cascade of growth biology operating across developmental ages. Cellular growth and differentiation are posited to be a process of integrative physiology, with increasing complexity in organismic growth achieved through modularity and temporally-differentiated signals. The flexible patterns of human growth are hypothesized to reflect the variability in timing and amount of growth saltations, which are the outcome of cross-talking signaling systems in an energy/immune integrating complex. This is an adaptive system, flexible and responsive to the challenges of developmental biology in changing environments.