What's the evolutionary purpose for people to have crooked teeth?

Small jaw: With diet changing to softer food, jaws have become smaller, therefore less room for teeth.

None: Jaws have reduced in size as humans have evolved but teeth have not changed much in their morphology. There is no purpose to this, it is just an effect of same size peg, but just a smaller hole.

No purpose: There is no purpose or benefit as far as an evolutionary trend. We just have less room in smaller jaws for the same amount of teeth. Something has to give and the teeth tend to get jumbled. There are other reasons for crooked teeth having nothing to do with that.

Other way around: Crooked teeth are a sign that: 1. Over eons of time our faces/jaws are getting smaller. Nature's way of compensating is eliminating teeth. Many people don't get 1 or more wisdom teeth, for example. 2. Another reason for the prevalence of crooked teeth in america is the melting pot factor. Our parent's genetic backgrounds vary widely, and the parts don't always fit when mixed together.