Subject. Going upright in human evolution changed the position of the spinal column and head. The position of the spine affects the occlusion through the rotational movements of the first cervical vertebra. The dentofacial system also evolved: the gaps disappeared between the canines and the adjacent teeth; sex differences of teeth were almost erased. As a result, the chewing became more adapted to speech reducing the dominant influence of the canines. Food influenced on the shape of teeth, the occlusion, the lower jaw movement. People use premolars and first molars for chewing soft food, which diminished the chewing efficiency of second molars. The function-dominant chew side also develops dentofacial system. Aim ― research regularities of jaw chewing in stress strain. Methods. Silicone occlusion impressions were obtained from each subject in stress conditions and physical activities. Results. Subjects with a dominant right hand have more amounts of match supracontacts at the right jaw side than at the left one. At opposite side of the spectrum, subjects with a dominant left hand have more amounts of match supracontacts at the left jaw side than at the right one. Ambidextrousnesses have approximately equal amounts at the right and left jaw sides. This is evidence of the force movement at the dominant chewing side. Conclusion. While subjects were falling, the low jaw moved forward resting up against on the canines. In other words, in weightlessness condition the falling subjects were searching for the point of support, which was the occlusion. In the results, it redirected and reduced the kinetic energy of falling bodies and levers of operating forces. The number of supracontact points during lifting is less than in the position of weightlessness. In other words, during the weight lifting the subjects have support points: the lower back and legs. And the occlusion becomes the third point of support only when lifting the extreme physical exertions.