Significance of adequate postural control in the appearance of habitual upright bipedal locomotion

Analysis of qualitative indicators of stability of the body during different types of locomotion in primates suggests that bipedal locomotion is not variation of some other type of locomotion. Transition from quadrupedal to bipedal locomotion is accompanied by a qualitative difference in body stability. Because of assuming an upright bipedal posture, the center of mass is lifted, the surface of the base of support is reduced, and the body structure does not provide passive stability in relation to inertial moments of the body around Y-axis. Additional head movements, trunk rotations, forelimb manipulations with objects and surveying the surroundings are necessary for survival, but they increase the degree of freedom of movement and further complicate the task of maintaining balance in the case of a postural change from erect quadrupedal to erect bipedal. This article presents a hypothesis that the transition from quadrupedal to habitual upright bipedal locomotion was caused by qualitative changes in the nervous system that allowed controlling the more demanding type of locomotion. The ability to control a more demanding posture increases possibilities of interactions between the organism and the complex environment and consequently increases the survival rate, breeding possibilities, and chances for occupying a new environmental niche. Existing data show that ability to execute the more demanding type of locomotion was made possible because of changes in the frontal lobe and pyramidal system. Only after the more demanding posture was enabled by changes in the nervous system, could advantages of bipedal over quadrupedal locomotion be utilized, including better scanning of the environment, carrying food and infants, simultaneous upper extremity movements and observation of the environment, limitless manipulation of objects with upper extremities above the individual, and less space for rotating around the Z-axis. The aforementioned advantages of habitual bipedal over quadrupedal locomotion are present in physically complex environments, such as the forest, which is associated with the appearance of habitual bipedal locomotion. (C) 2012 Elsevier Ltd. All rights reserved.Serbian Ministry of Science and Environmental Protection [175006/2011

Changes in the Anterior Presentation in Sheep Fetuses Due to Their Ventro-Sacral Position in the Second Half of Gestation

The hypothesis tested was that fetal postural development causes anterior presentation of the sheep fetus during a period of exclusive increase in anterior presentation. Exposing fetuses to a ventro-sacral position during a period of equal incidence of anterior and posterior presentations [50th-90th gestation day (GD)] should not cause changes in fetal presentation. During a period of an exclusive increase in anterior presentation (90th-140th GD) a ventro-sacral position should cause a 1800 turn of the fetus. Singleton gestations with fetus in anterior presentation were included. Ultrasound examinations consisted of three consecutive two minute scans to determine fetal presentation, and were conducted with the ewe in the following three positions: the upright quadrupedal position, sitting position in which the ewe's trunk is vertical to the ground; and again the upright quadrupedal position. The Mann-Whitney nonparametric U-test was used. On the 83rd GD (14 fetuses), there were no changes in fetal presentation, whereas on the 86th GD (10 fetuses) (p=0.035 p<0.05) and on the 116th GD (12 fetuses) (p=0.000 p<0.05) fetuses frequently assumed a transverse presentation at the second examination position. Further experiments would require the fetuses to be artificially maintained in a ventro-sacral position for a prolonged period.Serbian Ministry of Science and Environmental Protection [175006/2011

Changes in the Anterior Presentation in Sheep Fetuses Due to Their Ventro-Sacral Position in the Second Half of Gestation

The hypothesis tested was that fetal postural development causes anterior presentation of the sheep fetus during a period of exclusive increase in anterior presentation. Exposing fetuses to a ventro-sacral position during a period of equal incidence of anterior and posterior presentations [50th-90th gestation day (GD)] should not cause changes in fetal presentation. During a period of an exclusive increase in anterior presentation (90th-140th GD) a ventro-sacral position should cause a 1800 turn of the fetus. Singleton gestations with fetus in anterior presentation were included. Ultrasound examinations consisted of three consecutive two minute scans to determine fetal presentation, and were conducted with the ewe in the following three positions: the upright quadrupedal position, sitting position in which the ewe's trunk is vertical to the ground; and again the upright quadrupedal position. The Mann-Whitney nonparametric U-test was used. On the 83rd GD (14 fetuses), there were no changes in fetal presentation, whereas on the 86th GD (10 fetuses) (p=0.035 p<0.05) and on the 116th GD (12 fetuses) (p=0.000 p<0.05) fetuses frequently assumed a transverse presentation at the second examination position. Further experiments would require the fetuses to be artificially maintained in a ventro-sacral position for a prolonged period.Serbian Ministry of Science and Environmental Protection [175006/2011