Our descent from the treetops brought changes to the structure of our feet and the job that is required of them. In time, we began to do this exclusively on two legs. To accommodate these advances, we needed to make our way down from the trees in order to forage over greater distances. Our uprightness led to increased acuity of vision and the development of larger brains, which in turn required a wider-ranging diet including more high protein foods. Human evolution followed many different paths. Rather, they ground exclusively to the outside of the foot. Most importantly, weight is not placed their across the whole chimp foot.
What’s more, their pelvic muscles are much weaker than ours, so that they have to move their entire body from side to side with each step, just to keep their center of gravity over whichever leg is bearing weight. Chimps’ thigh bones slope outwards causing them to stand and walk with their feet wide apart. This led us to develop powerful pelvic muscles called gluteal abductors which stabilize our bodies while in mid-stride.
One reason for this is that our thigh bones slope inward from the hip to the knee, allowing the human foot to fall directly under our center of gravity. Our knuckle-dragging cousins use their hands to help them move forward, and although they can walk on two legs for short distances, their walk doesn’t much resemble ours. There are other important differences between the human skeleton and that of the chimpanzees. It is our lumbar spine’s lordotic or anterior curve that enables our upper body and feet to bear and transfer weight. Chimpanzees, our closest ancestors among the primates, have a flat lumbar spine and as a result can’t sustain upright posture. What allows humans to sustain these acts is the primary and secondary curves running through our whole body- most significantly those in the lumbar spine or lower back. Most primates can sit and stand, with some able to walk upright for short periods of time. Our transition to upright posture required significant adaptations of our muscles and bones.
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