According to a study conducted by researchers from Belgium and the UK, your shoes have probably shaped your feet to work differently than their original design.  They found that people who go through life unshod tend to have a wider forefoot, better weight distribution through the foot and they speculate, produce less impact as a result.

For a hit of how this might happen, try walking around on a hard floor without your shoes on and listen for the sound. More than likely, your heels are making a lot of noise when they hit the ground. This is often the result of wearing shoes with heel support. We tend to put our weight where we get the softest impact. But when we take our shoes off the padding is gone. When we’re barefoot, the impact of our bodies on our feet becomes our teacher. If you pick up your heel and poke it with your finger, you’ll notice that most of the padding is on the middle of the heel, not the back where you’re probably used to landing if you wear shoes (and who doesn’t!). Try walking letting the soft pad on the bottom of your heel land first. This isn’t easy if you’re used to it and the first thing you’ll probably notice is that you’re walking slower. Don’t worry though this is just the beginning of learning a gentler way to walk. The speed comes from the pushing off, but more about that later. For now, listen and feel if your walk is a little quieter or a little less hard on the rest of your body.