Fractal Development Theory: Phylogenetic Replay of Brain Weight in Ontogeny
A child's brain weight, stage by stage, retraces the brain sizes of our fossil ancestors, from the first hominins to Homo sapiens. Here is the pattern, the predictions, and the caveats.
We are publishing our hypothesis paper. Through eight years of independent research into developmental theory, we have physically advanced Montessori developmental theory. We would be happy if you could read it and provide us with your feedback.
By Hiroki Obara and Yachiko Obara (Polymath Research) · June 26, 2026
Abstract
This paper proposes a “Fractal Development Theory” that extends Maria Montessori’s developmental theory. Montessori’s developmental theory applied Ernst Haeckel’s recapitulation theory (”ontogeny recapitulates phylogeny”) to human development, and clarified developmental needs especially from early childhood through boyhood. This paper extends that work by focusing on **brain weight (approximately equal to cranial capacity)**, a more physical quantity, to argue that human developmental needs exhibit a fractal (self-similar) pattern tied to phylogeny. Specifically, the fetal period corresponds to the span from the origin of primitive life to the end of the arboreal life of the apes in the history of life, and development thereafter proceeds in a spiral with a cycle of roughly three years. Each stage of brain weight in ontogeny corresponds in steps to the cranial capacities of the human species seen in the fossil record. This theory contains falsifiable predictions (for example, the adult brain weight of Orrorin tugenensis should be about 400g, and Homo sapiens should have acquired recursive language by mutation), and it further answers why it is necessary to arrange an environment that meets developmental needs: because this is the least costly way to “replay” development. In addition, this theory explains human neoteny (the delay of maturation) as a consequence of ontogeny replaying the accumulation of phylogeny.
Keywords: fractal development, self-similarity, ontogeny and phylogeny, brain weight, recapitulation theory, Montessori developmental theory, developmental needs, falsifiable predictions
