Among all theories on human development, dynamic system theory is one of the newest and comprehensive ones. It was invented by Esther Thelen, the expert in developmental psychology. The theory originates from the field of mathematics where it describes the interrelations between components of a single unity and their flow. Applied to developmental psychology, dynamic systems theory suggests that development of a human at every possible stage, from molecular to cultural, and in different time domains is influenced by the extremely broad range of the external factors. Though it may seem quite abstract, dynamic system theory found its practical implementation in studying the development of infants at the early sensorimotor stage.
Dynamic systems theory emerged as Esther Thelen became dissatisfied with the existing explanations for infant motor behavior. According to previous theories, the behavior of infants is predetermined by the genetic developmental plan which is implemented step by step according to the cortical maturity of a child. Having conducted experiments with a small treadmill, the researcher revealed that stepping behaviors in infants 3 to 8 months-old develop due to the number of other factors than just a brain maturity. They include weight, a correlation between the amount of fat and muscles in the body, and external physical stimulators such as a treadmill.
Due to the experiments with infants, Esther Thelen concluded that human development is dynamic. While a behavior takes place in one moment, consequences of behavioral decisions accumulate for much longer, giving way to further progress. Development belongs on all the components of a system and their interaction between each other. Which is more, development is non-linear. Dynamic systems theory suggests that behavioral changes do not occur when they appear at a certain stage; they come when favorable conditions inside and outside of a human body allow them to happen.