The article offers an alternativě explanation of the course of motor development of the child, based on the basic biomechanical principles and, especially, leaming in different forms and at different levels. It makes it different from the prevailing opinion that the development is given by reieasing (maturation) of inherited (genetically determined) motor pattems. The main biomechanical factors are considered here to be the provision of posture against the acting gravitational force and the Bemstein principle of restriction and reieasing of DOF. In accordance with that the reactions of the child during the posturai tests are described as a reulsts of combination of four main factors: 1) gradually improving ability of controlled strengthening of the body, 2) disappearing of Moro reflex, 3) easing newbonVs flexion hypertonia and 4) the action of the gravitational force. In view of the extent the problém is divided in two independent parts. This first part includes intrauterine development, newbom period and the holokinetic stage of the suckling period

        Key words: motor pattern, posturai reactions, DOF, posture