People who do not wear shoes and socks or tights are said to be barefoot. Being barefoot is a natural way of walking. There are many receptors and muscles in the foot, which help sense the ground people are walking on. There's a thick layer of skin on the feet. This layer will get even thicker in people who often walk barefoot. This protection has its limits. Likely shoes were developed to protect against heat or cold. The oldest known traces of shoes date to about 8.500 years ago. People think some kinds of shoes were used when Europe was settled about 40.000 years ago.