Tuesday, June 13, 2017

Bipedalism, feet and shoes

Our ancestors have been walking upright (bipedal) for at least six million years. This is well supported by fossil evidence with the earliest bipedal footprints circa 3.66 million years ago, made by early hominids long before Homo sapiens, walked the Earth. The earliest indisputable evidence was found at Laetoli, close to Tanzania's Olduvai Gorge.

Some authorities believe there was a gradual transition from arboreal bipedalism to walking on the ground. This may have been forced upon tree dwellers due to changes in the geological landscape. Our early ancestors who lived in the tumultuous Rift Valley, were amidst unstable landscapes dotted with escarpments and crags. Living on the ground may have been a safer option particularly when climatic changes overtook.

Bipedal gait freed arms and hands for carrying and manipulating tools but exactly why and when standing upright on two feet started is shrouded in mystery. The scientific community remains divided but the long-standing and dominant theory suggests climate change several million years ago, was a key driver of the process. Our arboreal ancestors had to climb down from the trees to survive on the ground. These evolutionary processes meant there were several fundamental anatomical modifications to shift from four legs to two. The pelvis changed from being tall and flat from front to back to being much shorter and more bowl-shaped, giving better leverage for the muscles that move the hip in upright walking. The fossil record suggests the shift to walking on two legs might have occurred relatively early in our evolution.

The angle of the thigh bone changed to point inwards, bringing feet more directly under the centre of the bodies. Spines became more curved, forming a distinct S-shape and to facilitate body weight to lie over the hips and to cushion the brain while walking. Eventually the lower limbs also grew longer, allowing larger, more efficient steps. Feet too changed. Human toes became shorter and they line up with one another to create a lever to push off at the end of a step.

Standing allowed our ancestors to see over long grass to scan for predators and prey. The ancestral humans who were best at standing would have been more likely to survive and pass on their genes, so it is easy to imagine how natural selection could have resulted in a gradual shift from simply standing up briefly to permanently moving around in an upright posture.

Other researchers think standing upright helped our ancestors stay cool under the hot African sun. As a bonus, this idea might also help explain why our ancestors lost their hair to become naked apes. Standing up means only the top of the body needs to be protected with hair from the glare of the sun, while losing other body hair allows skin to cool more effectively in any breeze.

Recent 3 D analysis of early footprints reveal, the feet of our early ancestors made more than three million years ago, are not that different from the feet of today. Shoes it appears have had no adverse influence of the human foot.

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