Evolution of Human Posture and Bipedal Locomotion Within a Provisional Time Frame of Harsh Climate Changes

In this review paper several emerging issues related to development of human posture and locomotion are arranged in a provisional time frame. Accumulated evidences show that the Eurasian climate was often cold and arid with abundant dust in the atmosphere during the last 500 Ky. These dusty periods of cold, aridity and low insolation lasted from 360 to 340 Kya, 270 to 255 Kya, 170 to 130 Kya, 80 to 60 and finally 40 to 10 Kya. They coincide with migrations of Neanderthals and H. sapiens out of Africa, suggesting that harsh climates might have been important factors in forcing global migrations of our ancestors. When reaching the middle Eurasian latitudes, with reduced sun exposure due to dusty atmosphere and no sea food, our ancestors developed a deficit of vitamin D with compromised locomotion of young individuals due to rickets. This problem of bone maturation made a strong selection pressure toward lighter skin pigmentation. New evidences suggest that skin pigmentation genes in our genome came from the Neanderthals. They have survived several dusty periods, under the selection pressure of becoming pale skinned during their more than 400 Ky in Eurasia. On the other hand, H. sapiens came much later from Africa. Long-legged modern men could easily chase smaller prays, while groups of slower Neanderthals proambushed larger prays. Fossil evidence suggests that both hominid species lived in the same areas for thousands of years, until the final survivors turned out to be mixed individuals, possibly of Caucasian phenotype although with pale skin genes inherited from their Neanderthal ancestors