With regard to socio-psychology, the complexity of a human's neuronal function develops from initial primitive function to multimodal networking gradually through interaction between innate biological mechanisms and the surrounding environment. To study these developmental systems, we attempted to find a comparative-behavioral model among non-human primate species, common marmoset (Callithrix jacchus). In this research, we explored the correlation between the timing of change from involuntary- to voluntary-like movement in early stage and later the socio-emotional behavior, comparatively with the probable psychological development disabilities defined by our social behavior test (SBT). Using the 'Infant Antigravity Task (IAT)' and multivariate analysis, we quantitatively observed the neurological development from simple to complex behavior through interaction between motor and gravity environment. At the same time, we recorded the physiological and psychological development of two marmoset siblings (a male and a female) from their neonate stages to adult stages with their parents. In their lives, the male marmoset spontaneously showed his developmental delay in terms of body weight, blood glucose and socio-emotional difficulties under their own parental care. Based from the SBT results, the male demonstrated less social interaction with other family members compared to his sibling in the juvenile stage. Between these siblings, we looked for any predictable information in the earlier stage for future developmental issues particularly focusing on their behavioral expression during IAT from the 10th postnatal day until the 36th. day.Consequently, we found that both subjects expressed climbing-up behavior in the initial early period, but only the female who developed typically later, switched to jumping-down behavior with pre-facing to 'down' direction. Meanwhile, the male who would have developmental delay later, clearly did not show the switching pattern. The results suggest that the switch timing from involuntary to voluntary movement may be a possible predictor of juvenile and adolescent physiological and psychological retardation. The results also suggest that the primate model allows more methods to be developed for early detection of developmental disabilities that could be utilized in humans to pave the way for interventions and possible psychological or psychiatric treatment.