Homo Sapiens have always had the ability to walk upright. The key to this biological ability is our foot’s remarkable design. For example, short toes give us the ability to run long distances.
Surprisingly, another critical design feature appears to be the transverse tarsal arch — the horizontal curve that runs across the top of our foot. Not to be confused with the medial longitudinal arch running along the bottom side, the transverse arch accounts for more than 40 percent of the modern foot’s stiffness. But the two arches do work together, resulting in a unique support system which allows us to push off without falling over, a distinct difference from other animals that use flexible feet for grasping.
A team from the United States, Japan and the United Kingdom have been researching this through foot- bending experiments on cadavers. Then they developed a mathematical model to reconstruct the human foot’s history by comparing the modern arch with fossils from extinct hominins. Their conclusion is the transverse arch, which appeared in other hominins over three million years before us, was an important part of bipedalism. The medial longitudinal arch followed about 1.8 million years later. Put these two elements together and the human foot has the necessary stiffness that enables us to run and jump the way we do today!
For more detail, including how people with flat feet are affected, see “Why Human Feet Evolved Arches—and What Happens if You Lack Them ” by Sarah Elizabeth Richards (https://www.nationalgeographic.com/science/article/why-human-feet-evolved-arches-what-happens-if-you-lack-them?).