What factors contributed to the development of upright posture in humans?

As for the development of uprightness in a person, there are a number of hypotheses. The appearance of the S-shaped spine, vaulted foot, extended pelvis, and strong sacrum in human ancestors are hereditary changes that contributed to upright posture.
According to the hypothesis of Jan Lindblad, the ape-like human ancestors were forced to climb their hind limbs when searching for food in the water and when crossing water barriers to ford. Also, human ancestors were forced to climb down from trees to the ground due to climate and flora changes. To search for food in tall grass, they had to step up from all fours to their hind limbs.

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